Abstract: Loss of N7-methylguanosine (m7G) modification is involved in the recently discovered rapid tRNA degradation pathway. In yeast, this modification is catalyzed by the heterodimeric complex composed of a catalytic subunit Trm8 and a noncatalytic subunit Trm82. We have solved the crystal structure of Trm8 alone and in complex with Trm82. Trm8 undergoes subtle conformational changes upon Trm82 binding which explains the requirement of Trm82 for activity. Cocrystallization with the S-adenosyl-methionine methyl donor defines the putative catalytic site and a guanine binding pocket. Small-angle X-ray scattering in solution of the Trm8-Trm82 heterodimer in complex with tRNA(Phe) has enabled us to propose a low-resolution structure of the ternary complex which defines the tRNA binding mode of Trm8-Trm82 and the structural elements contributing to specificity.

Abstract: Emg1 was previously shown to be required for maturation of the 18S rRNA and biogenesis of the 40S ribosomal subunit. Here we report the determination of the crystal structure of Emg1 at 2 A resolution in complex with the methyl donor, S-adenosyl-methionine (SAM). This structure identifies Emg1 as a novel member of the alpha/beta knot fold methyltransferase (SPOUT) superfamily. In addition to the conserved SPOUT core, Emg1 has two unique domains that form an extended surface, which we predict to be involved in binding of RNA substrates. A point mutation within a basic patch on this surface almost completely abolished RNA binding in vitro. Three point mutations designed to disrupt the interaction of Emg1 with SAM each caused>100-fold reduction in SAM binding in vitro. Expression of only Emg1 with these mutations could support growth and apparently normal ribosome biogenesis in strains genetically depleted of Emg1. We conclude that the catalytic activity of Emg1 is not essential and that the presence of the protein is both necessary and sufficient for ribosome biogenesis.

Abstract: The extraordinary morphologies of viruses infecting hyperthermophilic archaea clearly distinguish them from bacterial and eukaryotic viruses. Moreover, their genomes code for proteins that to a large extend have no related sequences in the extent databases. However, a small pool of genes is shared by overlapping subsets of these viruses, and the most conserved gene, exemplified by the ORF109 of the Acidianus Filamentous Virus 3, AFV3, is present on genomes of members of three viral familes, the Lipothrixviridae, Rudiviridae, and "Bicaudaviridae", as well as of the unclassified Sulfolobus Turreted Icosahedral Virus, STIV. We present here the crystal structure of the protein (Mr = 13.1 kD, 109 residues) encoded by the AFV3 ORF 109 in two different crystal forms at 1.5 and 1.3 A resolution. The structure of AFV3-109 is a five stranded beta-sheet with loops on one side and three helices on the other. It forms a dimer adopting the shape of a cradle that encompasses the best conserved regions of the sequence. No protein with a related fold could be identified except for the ortholog from STIV1, whose structure was deposited at the Protein Data Bank. We could clearly identify a well bound glycerol inside the cradle, contacting exclusively totally conserved residues. This interaction was confirmed in solution by fluorescence titration. Although the function of AFV3-109 cannot be deduced directly from its structure, structural homology with the STIV1 protein, and the size and charge distribution of the cavity suggested it could interact with nucleic acids. Fluorescence quenching titrations also showed that AFV3-109 interacts with dsDNA. Genomic sequence analysis revealed bacterial homologs of AFV3-109 as a part of a putative previously unidentified prophage sequences in some Firmicutes.

Abstract: The South-Paris Yeast Structural Genomics Pilot Project (http://www.genomics.eu.org) aims at systematically expressing, purifying, and determining the three-dimensional structures of Saccharomyces cerevisiae proteins. We have already cloned 240 yeast open reading frames in the Escherichia coli pET system. Eighty-two percent of the targets can be expressed in E. coli, and 61% yield soluble protein. We have currently purified 58 proteins. Twelve X-ray structures have been solved, six are in progress, and six other proteins gave crystals. In this chapter, we present the general experimental flowchart applied for this project. One of the main difficulties encountered in this pilot project was the low solubility of a great number of target proteins. We have developed parallel strategies to recover these proteins from inclusion bodies, including refolding, coexpression with chaperones, and an in vitro expression system. A limited proteolysis protocol, developed to localize flexible regions in proteins that could hinder crystallization, is also described.

Abstract: The failure to produce and/or crystallize proteins is often due to their modular structure. There exists therefore considerable interest to develop strategies for tailoring proteins into crystallizable domains. In the framework of a Structural Genomics Project on soluble yeast proteins, we have tested the expression of numerous genetic constructs of our targets in order to produce and crystallize proteins and protein domains and solve their three-dimensional structure. In some cases, the choice of the domain boundaries was guided by prediction from sequence using various software packages, including Prelink, a home-made prediction method for detecting unfolded regions. In other cases, large numbers of constructs were generated using molecular biology or biochemical methods. In this paper, we analyze the results of the over-expression in E. coli and crystallization of these constructs, and compare these with the predictions that can be obtained from our software and from others.

Abstract: Naf1 is an essential protein involved in the maturation of box H/ACA ribonucleoproteins, a group of particles required for ribosome biogenesis, modification of spliceosomal small nuclear RNAs and telomere synthesis. Naf1 participates in the assembly of the RNP at transcription sites and in the nuclear trafficking of the complex. The crystal structure of a domain of yeast Naf1p, Naf1Delta1p, reveals a striking structural homology with the core domain of archaeal Gar1, an essential protein component of the mature RNP; it suggests that Naf1p and Gar1p have a common binding site on the enzymatic protein component of the particle, Cbf5p. We propose that Naf1p is a competitive binder for Cbf5p, which is replaced by Gar1p during maturation of the H/ACA particle. The exchange of Naf1p by Gar1p might be prompted by external factors that alter the oligomerisation state of Naf1p and Gar1p. The structural homology with Gar1 suggests that the function of Naf1 involves preventing non-cognate RNAs from being loaded during transport of the particle by inducing a non-productive conformation of Cbf5.

Abstract: The Kae1 (Kinase-associated endopeptidase 1) protein is a member of the recently identified transcription complex EKC and telomeres maintenance complex KEOPS in yeast. Kae1 homologues are encoded by all sequenced genomes in the three domains of life. Although annotated as putative endopeptidases, the actual functions of these universal proteins are unknown. Here we show that the purified Kae1 protein (Pa-Kae1) from Pyrococcus abyssi is an iron-protein with a novel type of ATP-binding site. Surprisingly, this protein did not exhibit endopeptidase activity in vitro but binds cooperatively to single and double-stranded DNA and induces unusual DNA conformational change. Furthermore, Pa-Kae1 exhibits a class I apurinic (AP)-endonuclease activity (AP-lyase). Both DNA binding and AP-endonuclease activity are inhibited by ATP. Kae1 is thus a novel and atypical universal DNA interacting protein whose importance could rival those of RecA (RadA/Rad51) in the maintenance of genome integrity in all living cells.

Abstract: The Saccharomyces cerevisiae His6 gene codes for the enzyme phosphoribosyl-5-amino-1-phosphoribosyl-4-imidazolecarboxamide isomerase, catalyzing the fourth step in histidine biosynthesis. To get an insight into the structure and function of this enzyme, we determined its X-ray structure at a resolution of 1.30 A using the anomalous diffraction signal of the protein's sulphur atoms at 1.77 A wavelength. His6 folds in an (alpha/beta)8 barrel similar to HisA, which performs the same function in bacteria and archaea. We found a citrate molecule from the buffer bound in a pocket near the expected position of the active site and used it to model the open form of the substrate (phosphoribulosyl moiety), which is a reaction intermediate. This model enables us to identify catalytic residues and to propose a reaction mechanism where two aspartates act as acid/base catalysts: Asp134 as a proton donor for ring opening, and Asp9 as a proton acceptor and donor during enolization of the aminoaldose. Asp9 is conserved in yeast His6 and bacterial or archaeal HisA sequences, and Asp134 has equivalents in both HisA and TrpF, but they occur at a different position in the protein sequence.

Abstract: Human multidrug resistance protein 1 (MRP1) is a membrane protein that belongs to the ATP-binding cassette (ABC) superfamily of transport proteins. MRP1 contributes to chemotherapy failure by exporting a wide range of anti-cancer drugs when over expressed in the plasma membrane of cells. Here, we report the first high-resolution crystal structure of human MRP1-NBD1. Drug efflux requires energy resulting from hydrolysis of ATP by nucleotide binding domains (NBDs). Contrary to the prokaryotic NBDs, the extremely low intrinsic ATPase activity of isolated MRP1-NBDs allowed us to obtain the structure of wild-type NBD1 in complex with Mg2+/ATP. The structure shows that MRP1-NBD1 adopts a canonical fold, but reveals an unexpected non-productive conformation of the catalytic site, providing an explanation for the low intrinsic ATPase activity of NBD1 and new hypotheses on the cooperativity of ATPase activity between NBD1 and NBD2 upon heterodimer formation.

Abstract: The yeast Set1 histone H3 lysine 4 (H3K4) methyltransferase contains, in addition to its catalytic SET domain, a conserved RNA recognition motif (RRM1). We present here the crystal structure and the secondary structure assignment in solution of the Set1 RRM1. Although RRM1 has the expected betaalphabetabetaalphabeta RRM-fold, it lacks the typical RNA-binding features of these modules. RRM1 is not able to bind RNA by itself in vitro, but a construct combining RRM1 with a newly identified downstream RRM2 specifically binds RNA. In vivo, H3K4 methylation is not affected by a point mutation in RRM2 that preserves Set1 stability but affects RNA binding in vitro. In contrast mutating RRM1 destabilizes Set1 and leads to an increase of dimethylation of H3K4 at the 5'-coding region of active genes at the expense of trimethylation, whereas both, dimethylation decreases at the 3'-coding region. Taken together, our results suggest that Set1 RRMs bind RNA, but Set1 RNA-binding activity is not linked to H3K4 methylation.

Abstract: A large-scale programme has been embarked upon aiming towards the structural determination of conserved proteins from viruses infecting hyperthermophilic archaea. Here, the crystallization of protein 14 from the archaeal virus SIFV is reported. This protein, which contains 111 residues (MW 13 465 Da), was cloned and expressed in Escherichia coli with an N-terminal His(6) tag and purified to homogeneity. The tag was subsequently cleaved and the protein was crystallized using PEG 1000 or PEG 4000 as a precipitant. Large crystals were obtained of the native and the selenomethionine-labelled protein using sitting drops of 100-300 nl. Crystals belong to space group P6(2)22 or P6(4)22, with unit-cell parameters a = b = 68.1, c = 132.4 A. Diffraction data were collected to a maximum acceptable resolution of 2.95 and 3.20 A for the SeMet-labelled and native protein, respectively.

Abstract: Despite the generation of a large amount of sequence information over the last decade, more than 40% of well characterized enzymatic functions still lack associated protein sequences. Assigning protein sequences to documented biochemical functions is an interesting challenge. We illustrate here that structural genomics may be a reasonable approach in addressing these questions. We present the crystal structure of the Saccharomyces cerevisiae YMR099cp, a protein of unknown function. YMR099cp adopts the same fold as galactose mutarotase and shares the same catalytic machinery necessary for the interconversion of the alpha and beta anomers of galactose. The structure revealed the presence in the active site of a sulfate ion attached by an arginine clamp made by the side chain from two strictly conserved arginine residues. This sulfate is ideally positioned to mimic the phosphate group of hexose 6-phosphate. We have subsequently successfully demonstrated that YMR099cp is a hexose-6-phosphate mutarotase with broad substrate specificity. We solved high resolution structures of some substrate enzyme complexes, further confirming our functional hypothesis. The metabolic role of a hexose-6-phosphate mutarotase is discussed. This work illustrates that structural information has been crucial to assign YMR099cp to the orphan EC activity: hexose-phosphate mutarotase.

Abstract: PTPA, an essential and specific activator of protein phosphatase 2A (PP2A), functions as a peptidyl prolyl isomerase (PPIase). We present here the crystal structures of human PTPA and of the two yeast orthologs (Ypa1 and Ypa2), revealing an all alpha-helical protein fold that is radically different from other PPIases. The protein is organized into two domains separated by a groove lined by highly conserved residues. To understand the molecular mechanism of PTPA activity, Ypa1 was cocrystallized with a proline-containing PPIase peptide substrate. In the complex, the peptide binds at the interface of a peptide-induced dimer interface. Conserved residues of the interdomain groove contribute to the peptide binding site and dimer interface. Structure-guided mutational studies showed that in vivo PTPA activity is influenced by mutations on the surface of the peptide binding pocket, the same mutations that also influenced the in vitro activation of PP2Ai and PPIase activity.

Abstract: Crystallization has long been regarded as one of the major bottlenecks in high-throughput structural determination by X-ray crystallography. Structural genomics projects have addressed this issue by using robots to set up automated crystal screens using nanodrop technology. This has moved the bottleneck from obtaining the first crystal hit to obtaining diffraction-quality crystals, as crystal optimization is a notoriously slow process that is difficult to automatize. This article describes the high-throughput optimization strategies used in the Yeast Structural Genomics project, with selected successful examples.

Abstract: We determined the three-dimensional crystal structure of the protein YML079wp, encoded by a hypothetical open reading frame from Saccharomyces cerevisiae to a resolution of 1.75 A. The protein has no close homologs and its molecular and cellular functions are unknown. The structure of the protein is a jelly-roll fold consisting of ten beta-strands organized in two parallel packed beta-sheets. The protein has strong structural resemblance to the plant storage and ligand binding proteins (canavalin, glycinin, auxin binding protein) but also to some plant and bacterial enzymes (epimerase, germin). The protein forms homodimers in the crystal, confirming measurements of its molecular mass in solution. Two monomers have their beta-sheet packed together to form the dimer. The presence of a hydrophobic ligand in a well conserved pocket inside the barrel and local sequence similarity with bacterial epimerases may suggest a biochemical function for this protein.

Abstract: Yhr049w/FSH1 was recently identified in a combined computational and experimental proteomics analysis for the detection of active serine hydrolases in yeast. This analysis suggested that FSH1 might be a serine-type hydrolase belonging to the broad functional alphabeta-hydrolase superfamily. In order to get insight into the molecular function of this gene, it was targeted in our yeast structural genomics project. The crystal structure of the protein confirms that it contains a Ser/His/Asp catalytic triad that is part of a minimal alpha/beta-hydrolase fold. The architecture of the putative active site and analogies with other protein structures suggest that FSH1 may be an esterase. This finding was further strengthened by the unexpected presence of a compound covalently bound to the catalytic serine in the active site. Apparently, the enzyme was trapped with a reactive compound during the purification process.

Abstract: Structural genomics aims at the establishment of a universal protein-fold dictionary through systematic structure determination either by NMR or X-ray crystallography. In order to catch up with the explosive amount of protein sequence data, the structural biology laboratories are spurred to increase the speed of the structure-determination process. To achieve this goal, high-throughput robotic approaches are increasingly used in all the steps leading from cloning to data collection and even structure interpretation is becoming more and more automatic. The progress made in these areas has begun to have a significant impact on the more 'classical' structural biology laboratories, dramatically increasing the number of individual experiments. This automation creates the need for efficient data management. Here, a new piece of software, HalX, designed as an 'electronic lab book' that aims at (i) storage and (ii) easy access and use of all experimental data is presented. This should lead to much improved management and tracking of structural genomics experimental data.

Abstract: In the Pseudomonas bacterial genomes, the PhzF proteins are involved in the production of phenazine derivative antibiotic and antifungal compounds. The PhzF superfamily however also encompasses proteins in all genomes from bacteria to eukaryotes, for which no function has been assigned. We have determined the three dimensional crystal structure at 2.05 A resolution of YHI9, the yeast member of the PhzF family. YHI9 has a fold similar to bacterial diaminopimelate epimerase, revealing a bimodular structure with an internal symmetry. Residue conservation identifies a putative active site at the interface between the two domains. Evolution of this protein by gene duplication, gene fusion and domain swapping from an ancestral gene containing the "hot dog" fold, identifies the protein as a "kinked double hot dog" fold.

Abstract: We present here the structure of Yer010c protein of unknown function, solved by Multiple Anomalous Diffraction and revealing a common fold and oligomerization state with proteins of the regulator of ribonuclease activity A (RraA) family. In Escherichia coli, RraA has been shown to regulate the activity of ribonuclease E by direct interaction. The absence of ribonuclease E in yeast suggests a different function for this family member in this organism. Yer010cp has a few supplementary secondary structure elements and a deep pseudo-knot at the heart of the protein core. A tunnel at the interface between two monomers, lined with conserved charged residues, has unassigned residual electron density and may constitute an active site for a yet unknown activity.

Abstract: We have determined the three-dimensional crystal structure of the protein encoded by the open reading frame YFL030w from Saccharomyces cerevisiae to a resolution of 2.6 A using single wavelength anomalous diffraction. YFL030w is a 385 amino-acid protein with sequence similarity to the aminotransferase family. The structure of the protein reveals a homodimer adopting the fold-type I of pyridoxal 5'-phosphate (PLP)-dependent aminotransferases. The PLP co-factor is covalently bound to the active site in the crystal structure. The protein shows close structural resemblance with the human alanine:glyoxylate aminotransferase (EC 2.6.1.44), an enzyme involved in the hereditary kidney stone disease primary hyperoxaluria type 1. In this paper we show that YFL030w codes for an alanine:glyoxylate aminotransferase, highly specific for its amino donor and acceptor substrates.

Abstract: Ribose-5-phosphate isomerase A has an important role in sugar metabolism by interconverting ribose-5-phosphate and ribulose-5-phosphate. This enzyme is ubiquitous and highly conserved among the three kingdoms of life. We have solved the 2.1 A resolution crystal structure of the Saccharomyces cerevisiae enzyme by molecular replacement. This protein adopts the same fold as its archaeal and bacterial orthologs with two alpha/beta domains tightly packed together. Mapping of conserved residues at the surface of the protein reveals strong invariability of the active site pocket, suggesting a common ligand binding mode and a similar catalytic mechanism. The yeast enzyme associates as a homotetramer similarly to the archaeal protein. The effect of an inactivating mutation (Arg189 to Lys) is discussed in view of the information brought by this structure.

Abstract: The protein product of the YGR205w gene of Saccharomyces cerevisiae was targeted as part of our yeast structural genomics project. YGR205w codes for a small (290 amino acids) protein with unknown structure and function. The only recognizable sequence feature is the presence of a Walker A motif (P loop) indicating a possible nucleotide binding/converting function. We determined the three-dimensional crystal structure of Se-methionine substituted protein using multiple anomalous diffraction. The structure revealed a well known mononucleotide fold and strong resemblance to the structure of small metabolite phosphorylating enzymes such as pantothenate and phosphoribulo kinase. Biochemical experiments show that YGR205w binds specifically ATP and, less tightly, ADP. The structure also revealed the presence of two bound sulphate ions, occupying opposite niches in a canyon that corresponds to the active site of the protein. One sulphate is bound to the P-loop in a position that corresponds to the position of beta-phosphate in mononucleotide protein ATP complex, suggesting the protein is indeed a kinase. The nature of the phosphate accepting substrate remains to be determined.

Abstract: Chorismate synthase (EC 4.2.3.5), the seventh enzyme in the shikimate pathway, catalyzes the transformation of 5-enolpyruvylshikimate 3-phosphate (EPSP) to chorismate, which is the last common precursor in the biosynthesis of numerous aromatic compounds in bacteria, fungi, and plants. The chorismate synthase reaction involves a 1,4-trans-elimination of phosphoric acid from EPSP and has an absolute requirement for reduced FMN as a cofactor. We have determined the three-dimensional x-ray structure of the yeast chorismate synthase from selenomethionine-labeled crystals at 2.2-A resolution. The structure shows a novel betaalphabetaalpha fold consisting of an alternate tight packing of two alpha-helical and two beta-sheet layers, showing no resemblance to any documented protein structure. The molecule is arranged as a tight tetramer with D2 symmetry, in accordance with its quaternary structure in solution. Electron density is missing for 23% of the amino acids, spread over sequence regions that in the three-dimensional structure converge on the surface of the protein. Many totally conserved residues are contained within these regions, and they probably form a structured but mobile domain that closes over a cleft upon substrate binding and catalysis. This hypothesis is supported by previously published spectroscopic measurements implying that the enzyme undergoes considerable structural changes upon binding of both FMN and EPSP.

Abstract: The important role of the serine/threonine protein phosphatase 2A (PP2A) in various cellular processes requires a precise and dynamic regulation of PP2A activity, localization, and substrate specificity. The regulation of the function of PP2A involves the reversible methylation of the COOH group of the C-terminal leucine of the catalytic subunit, which, in turn, controls the enzyme's heteromultimeric composition and confers different protein recognition and substrate specificity. We have determined the structure of PPM1, the yeast methyltransferase responsible for methylation of PP2A. The structure of PPM1 reveals a common S-adenosyl-l-methionine-dependent methyltransferase fold, with several insertions conferring the specific function and substrate recognition. The complexes with the S-adenosyl-l-methionine methyl donor and the S-adenosyl-l-homocysteine product and inhibitor unambiguously revealed the co-substrate binding site and provided a convincing hypothesis for the PP2A C-terminal peptide binding site. The structure of PPM1 in a second crystal form provides clues to the dynamic nature of the PPM1/PP2A interaction.

Abstract: Allantoicase (EC 3.5.3.4) catalyzes the conversion of allantoate into ureidoglycolate and urea, one of the final steps in the degradation of purines to urea. The mechanism of most enzymes involved in this pathway, which has been known for a long time, is unknown. In this paper we describe the three-dimensional crystal structure of the yeast allantoicase determined at a resolution of 2.6 A by single anomalous diffraction. This constitutes the first structure for an enzyme of this pathway. The structure reveals a repeated jelly roll beta-sheet motif, also present in proteins of unrelated biochemical function. Allantoicase has a hexameric arrangement in the crystal (dimer of trimers). Analysis of the protein sequence against the structural data reveals the presence of two totally conserved surface patches, one on each jelly roll motif. The hexameric packing concentrates these patches into conserved pockets that probably constitute the active site.

Abstract: The ORF YDR533c from Saccharomyces cerevisiae codes for a 25.5 kDa protein of unknown biochemical function. Transcriptome analysis of yeast has shown that this gene is activated in response to various stress conditions together with proteins belonging to the heat shock family. In order to clarify its biochemical function, we determined the crystal structure of YDR533c to 1.85 A resolution by the single anomalous diffraction method. The protein possesses an alpha/beta hydrolase fold and a putative Cys-His-Glu catalytic triad common to a large enzyme family containing proteases, amidotransferases, lipases, and esterases. The protein has strong structural resemblance with the E. coli Hsp31 protein and the intracellular protease I from Pyrococcus horikoshii, which are considered class I and class III members of the Hsp31 family, respectively. Detailed structural analysis strongly suggests that the YDR533c protein crystal structure is the first one of a class II member of the Hsp31 family.

Abstract: We present here the outlines and results from our yeast structural genomics (YSG) pilot-project. A lab-scale platform for the systematic production and structure determination is presented. In order to validate this approach, 250 non-membrane proteins of unknown structure were targeted. Strategies and final statistics are evaluated. We finally discuss the opportunity of structural genomics programs to contribute to functional biochemical annotation.

Abstract: Rnt1 endoribonuclease, the yeast homolog of RNAse III, plays an important role in the maturation of a diverse set of RNAs. The enzymatic activity requires a conserved catalytic domain, while RNA binding requires the double-stranded RNA-binding domain (dsRBD) at the C-terminus of the protein. While bacterial RNAse III enzymes cleave double-stranded RNA, Rnt1p specifically cleaves RNAs that possess short irregular stem-loops containing 12-14 base pairs interrupted by internal loops and bulges and capped by conserved AGNN tetraloops. Consistent with this substrate specificity, the isolated Rnt1p dsRBD and the 30-40 amino acids that follow bind to AGNN-containing stem-loops preferentially in vitro. In order to understand how Rnt1p recognizes its cognate processing sites, we have defined its minimal RNA-binding domain and determined its structure by solution NMR spectroscopy and X-ray crystallography. We observe a new carboxy-terminal helix following a canonical dsRBD structure. Removal of this helix reduces binding to Rnt1p substrates. The results suggest that this helix allows the Rnt1p dsRBD to bind to short RNA stem-loops by modulating the conformation of helix alpha1, a key RNA-recognition element of the dsRBD.

Abstract: Flavodoxins are involved in a variety of electron transfer reactions that are essential for life. Although FMN-binding proteins are well characterized in prokaryotic organisms, information is scarce for eukaryotic flavodoxins. We describe the 2.0-A resolution crystal structure of the Saccharomyces cerevisiae YLR011w gene product, a predicted flavoprotein. YLR011wp indeed adopts a flavodoxin fold, binds the FMN cofactor, and self-associates as a homodimer. Despite the absence of the flavodoxin key fingerprint motif involved in FMN binding, YLR011wp binds this cofactor in a manner very analogous to classical flavodoxins. YLR011wp closest structural homologue is the homodimeric Bacillus subtilis Yhda protein (25% sequence identity) whose homodimer perfectly superimposes onto the YLR011wp one. Yhda, whose function is not documented, has 53% sequence identity with the Bacillus sp. OY1-2 azoreductase. We show that YLR011wp has an NAD(P)H-dependent FMN reductase and a strong ferricyanide reductase activity. We further demonstrate a weak but specific reductive activity on azo dyes and nitrocompounds.

Abstract: A canonical structural genomics programme is being conducted at the Paris-Sud campus area on baker's yeast proteins. Experimental strategies, first results and identified bottlenecks are presented. The actual or potential contributions to the structural genomics of several experimental structure-determination methods are discussed.

Abstract: Phox homology (PX) domains have been recently identified in a number of different proteins and are involved in various cellular functions such as vacuolar targeting and membrane protein trafficking. It was shown that these modules of about 130 amino acids specifically binding to phosphoinositides and that this interaction is crucial for their cellular function. The yeast genome contains 17 PX domain proteins. One of these, Grd19p, is involved in the localization of the late Golgi membrane proteins DPAP A and Kex2p. Grd19p consists of the PX domain with 30 extra residues at the N-terminal and is homologous to the functionally characterized human sorting nexin protein SNX3. We determined the 2.0 A crystal structure of Grd19p in the free form and in complex with d-myo-phosphatidylinositol 3-phosphate (diC4PtdIns(3)P), representing the first case of both free and ligand-bound conformations of the same PX module. The ligand occupies a well defined positively charged binding pocket at the interface between the beta-sheet and alpha-helical parts of the molecule. The structure of the free and bound protein are globally similar but show some significant differences in a region containing a polyproline peptide and a putative membrane attachment site.

Abstract: The ribonucleoprotein enzyme telomerase maintains chromosome ends in most eukaryotes and is critical for a cell's genetic stability and its proliferative viability. All telomerases contain a catalytic protein component homologous to viral reverse transcriptases (TERT) and an RNA (TR) that provides the template sequence as well as a scaffold for ribonucleoprotein assembly. Vertebrate telomerase RNAs have three essential domains: the template, activation and stability domains. Here we report the NMR structure of an essential RNA element derived from the human telomerase RNA activation domain. The sequence forms a stem-loop structure stabilized by a GU wobble pair formed by two of the five unpaired residues capping a short double helical region. The remaining three loop residues are in a well-defined conformation and form phosphate-base stacking interactions reminiscent of other RNA loop structures. Mutations of these unpaired nucleotides abolish enzymatic activity. The structure rationalizes a number of biochemical observations, and allows us to propose how the loop may function in the telomerase catalytic cycle. The pre-formed structure of the loop exposes the bases of these three essential nucleotides and positions them to interact with other RNA sequences within TR, with the reverse transcriptase or with the newly synthesized telomeric DNA strand. The functional role of this stem-loop appears to be conserved in even distantly related organisms such as yeast and ciliates.

Abstract:

Abstract: High resolution NMR data on UNCG and GNRA tetraloops (where N is any of the four nucleotides and R is a purine) have shown that they contain ribonucleosides with unusual 2'-endo/anti and 3'-endo/syn conformations, in addition to the 3'-endo/anti ones which are regularly encountered in RNA chains. In the current study, Raman spectroscopy has been used to probe these nucleoside conformations and follow the order (hairpin) to disorder (random chain) structural transitions in aqueous phase in the 5-80 degreesC temperature range. Spectral evolution of GCAA and GAAA tetraloops, as formed in very short hairpins with only three G.C base pairs in their stems (T m >60 degreesC), are reported and compared with those previously published on UUCG and UACG tetraloops, for which the syn orientation of the terminal guanine as well as the 2'-endo/anti conformation of the third rC residue have been confirmed by means of vibrational marker bands. Raman data obtained as a function of temperature show that the first uracil in the UUCG tetraloop is stacked and the two middle residues (rU and rC) are in the 2'-endo/anti conformation, in agreement with the previously published NMR results. As far as the new data concerning the GNRA type tetraloops are concerned, they lead us to conclude that: (i) in both cases (GCAA and GAAA tetraloops) the adenine bases are stacked; (ii) the second rC residue in the GCAA tetraloop has a 3'-endo/anti conformation; (iii) the sugar pucker associated with the third rA residue in both tetraloops possibly undergoes a 3'-endo/2'-endo interconversion as predicted by NMR results; (iv) the stem adopts a regular A-form structure; (v) all other nucleosides of these two GNRA tetraloops possess the usual 3'-endo/anti conformation.

Abstract: Structures of the UCCG and UGCG tetraloops formed in octamer ribonucleotidic hairpin sequences, i.e., 5'-r[GC(UCCG)GC]-3' and 5'-r[GC(UGCG)GC]-3', have been studied in aqueous solution by methods of optical spectroscopy. UV absorption melting profiles of these short hairpins, containing only two closing GC base pairs in the stem, are consistent with a monophasic, completely reversible order-to-disorder transition and clearly confirm their unusual structural stability (with Tm congruent with 50 degrees C). To establish structural characteristics of these tetraloops, Raman and FTIR spectroscopies have been used and vibrational conformation markers arising from the phosphate backbone and various nucleosides have been analyzed. They have been assigned on the basis of known unambiguous vibrational markers established for DNA and RNA chains. Surprisingly, they are easily transferable to short oligonucleotidic sequences. Intensities and wavenumbers of these conformation markers have been monitored in the 0-70 degrees C temperature range, i.e., in going from an ordered to a disordered structure. The main structural features of the UCCG and UGCG tetraloops are similar to those previously found in the UUCG and UACG tetraloops by means of NMR and vibrational spectroscopies, except those of the second nucleosides of the tetraloops (rC and rG, respectively) which adopt a 3'-endo/anti rather than a 2'-endo/anti conformation.