Abstract: Escherichia coli represents a robust, inexpensive expression host for the production of recombinant proteins. However, one major limitation is that certain protein classes do not express well in a biologically relevant form using standard expression approaches in the cytoplasm of E. coli. To improve the usefulness of the E. coli expression platform we have investigated combinations of promoters and selected N-terminal fusion tags for the extracellular expression of human target proteins. A comparative study was conducted on 24 target proteins fused to outer membrane protein A (OmpA), outer membrane protein F (OmpF) and osmotically inducible protein Y (OsmY). Based on the results of this initial study, we carried out an extended expression screen employing the OsmY fusion and multiple constructs of a more diverse set of human proteins. Using this high-throughput compatible system, we clearly demonstrate that secreted biomedically relevant human proteins can be efficiently retrieved and purified from the growth medium.
Abstract: Ligation-independent cloning (LIC) allows for cloning of DNA constructs independent of insert restriction sites and ligases. However, any required mutations are typically introduced by additional, time-consuming steps. We present a rapid, inexpensive method for mutagenesis in the 5' LIC site of expression constructs and report on the construction of expression vectors with N-terminal serine, cysteine, threonine, or tyrosine residues after tobacco etch virus (TEV) protease cleavage. In a practical application, the N-terminal serine was oxidized to an aldehyde, subsequently reacted with an amino-oxy functionalized polyethylene glycol (PEG) ligand under aniline catalysis to provide a protein selectively modified at the N-terminus.
Abstract: Soluble expression of proteins in a relevant form for functional and structural investigations still often remains a challenge. Although many biochemical factors are known to affect solubility, a thorough investigation of yield-limiting factors is normally not feasible in high-throughput efforts. Here we present a screening strategy for expression of biomedically relevant proteins in Escherichia coli using a panel of six different genetic variations. These include engineered strains for rare codon supplementation, increased disulfide bond formation in the cytoplasm and novel vectors for secretion to the periplasm or culture medium. Combining these variants with expression construct truncations design, we report on parallel cloning and expression of more than 300 constructs representing 24 selected proteins; including full-length variants of human growth factors, interleukins and growth factor binding proteins. This rapid screening approach appears highly suitable for high-throughput efforts targeting either large sets of proteins or more focused investigations regarding individual high-profile targets.
Abstract: Affibody molecules binding to the site of hormone interaction in IGF-1R (insulin-like growth factor-1 receptor) were successfully selected by phage-display technology employing a competitive-elution strategy during biopanning, whereby release of receptor-bound phagemids was accomplished by competition with IGF-1 (insulin-like growth factor-1). In non-competitive selections, the elution of receptor-bound phagemids was performed by imidazole or low-pH incubation, which also resulted in the isolation of affibody molecules that could bind to the receptor. An ELISA-based assay showed that the affibody molecules generated by IGF-1 competition during elution, in addition to affibody molecules generated in the non-competitive selections, could compete with IGF-1 for binding to the receptor. The affinities of the isolated variants to IGF-1R-overexpressing MCF-7 cells were determined and ranged from high nanomolar to 2.3 nM. The most promising variant, Z4:40, was shown to recognize IGF-1R efficiently in several different contexts: in analyses based on flow cytometry, fluorescence microscopy and receptor pull-down from cell extracts. In addition, when Z4:40 was added to the medium of MCF-7 cells that were dependent on IGF-1 for efficient growth, it was found to have a dose-dependent growth-inhibitory effect on the cells. Applications of affibody-based reagents for quantitative and qualitative analyses of IGF-1R status, as well as applications of affibody-based reagents for therapy, are discussed.
Abstract: Development of molecules with the ability to selectively inhibit particular protein-protein interactions is important in providing tools for understanding cell biology. In this work, we describe efforts to select small Ras- and Raf-specific three-helix bundle affibody binding proteins capable of inhibiting the interaction between H-Ras and Raf-1, from a combinatorial library displayed on bacteriophage. Target-specific variants with typically high nanomolar or low micromolar affinities (K(D)) could be selected successfully against both proteins, as shown by dot blot, ELISA and real-time biospecific interaction analyses. Affibody molecule variants selected against H-Ras were shown to bind epitopes overlapping each other at a site that differed from that at which H-Ras interacts with Raf-1. In contrast, an affibody molecule isolated during selection against Raf-1 was shown to effectively inhibit the interaction between H-Ras and Raf-1 in a dose-dependent manner. Possible intracellular applications of the selected affibody molecules are discussed.
Abstract: Abnormal activity of the epidermal growth factor receptor (EGFR) is associated with various cancer-related processes and motivates the search for strategies that can selectively block EGFR signalling. In this study, functional knockdown of EGFR was achieved through expression of an affibody construct, (ZEGFR:1907)(2-)KDEL, with high affinity for EGFR and extended with the amino acids KDEL to make it resident in the secretory compartments. Expression of (ZEGFR:1907)(2-)KDEL resulted in 80% reduction ofthe cell surface level of EGFR, and fluorescent staining for EGFR and the (ZEGFR:1907)(2-)KDEL construct showed overlapping intracellular localisation. Immunocapture of EGFR from cell lysates showed that an intracellular complex between EGFR and the affibody construct had been formed, further indicating aspecific interaction between the affibody construct and EGFR. Surface depletion of EGFR led to a dramatic decrease in the amount of kinase domain phosphorylated EGFR, coincident with a significant decrease in the proliferation rate.
Abstract: Interference with the export of cell surface receptors can be performed through co-expression of specific affinity molecules designed for entrapment in the endoplasmic reticulum during the export process. We describe the investigation of a small (6 kDa) non-immunoglobulin-based HER2 receptor binding affibody molecule (Z(HER2:00477)), for use in affinity mediated entrapment of the HER2 receptor in the ER. Constructs encoding Z(HER2:00477) or a control affibody protein, with or without ER-retention peptide extensions (KDEL), were expressed in the HER2 over-expressing cell line SKOV-3. Intracellular expression of the full-length affibody constructs could be confirmed by probing cell extracts by Western blotting. Confocal immunofluorescence microscopy experiments showed extensive co-localization of the HER2 receptor and Z(HER2:00477)-KDEL in the ER, whereas the use of a KDEL-extended control affibody molecule resulted in distinct and separate signals from cell surface-localized HER2 receptor and ER-localized affibody protein. This indicated a capability of the Z(HER2:00477)-KDEL fusion protein to functionally interfere with the export process of HER2 receptor in a specific manner. Using flow cytometry and cell proliferation analyses, it could be shown that expression of the Z(HER2:00477)-KDEL fusion construct in the SKOV-3 cell line resulted both in a marked reduction in cell surface level of HER2 receptors and that the cell population doubling time was significantly increased. Expression of the Z(HER2:00477)-KDEL fusion protein in additional cell lines of different origin and with different expression levels of endogenous HER2 receptor compared to SKOV-3, also resulted in depletion of the cell surface levels of HER2 receptor. This indicated upon a general ability of the Z(HER2:00477)-KDEL fusion protein to functionally interfere with the export process of HER2.
