An automated peptide and protein thiazolidine coupling chemistry for biosensor immobilization giving a unique N-terminal orientation

α-Oxo aldehyde or glyoxylyl group chemistry in peptide bioconjugation

Since the 1990s, α-oxo aldehyde or glyoxylic acid chemistry has inspired a vast array of synthetic tools for tailoring peptide or protein structures, for developing peptides endowed with novel physicochemical properties or biological functions, for assembling a large diversity of bioconjugates or hybrid materials, or for designing peptide-based micro or nanosystems. This past decade, important developments have enriched the α-oxo aldehyde synthetic tool box in peptide bioconjugation chemistry and explored novel applications. The aim of this review is to give a large overview of this creative field.

Antibodies specifically targeting a locally misfolded region of tumor associated EGFR

Epidermal Growth Factor Receptor (EGFR) is involved in stimulating the growth of many human tumors, but the success of therapeutic agents has been limited in part by interference from the EGFR on normal tissues. Previously, we reported an antibody (mab806) against a truncated form of EGFR found commonly in gliomas. Remarkably, it also recognizes full-length EGFR on tumor cells but not on normal cells. However, the mechanism for this activity was unclear. Crystallographic structures for Fab:EGFR(287-302) complexes of mAb806 (and a second, related antibody, mAb175) show that this peptide epitope adopts conformations similar to those found in the wtEGFR. However, in both conformations observed for wtEGFR, tethered and untethered, antibody binding would be prohibited by significant steric clashes with the CR1 domain. Thus, these antibodies must recognize a cryptic epitope in EGFR. Structurally, it appeared that breaking the disulfide bond preceding the epitope might allow the CR1 domain to open up sufficiently for antibody binding. The EGFR(C271A/C283A) mutant not only binds mAb806, but binds with 1:1 stoichiometry, which is significantly greater than wtEGFR binding. Although mAb806 and mAb175 decrease tumor growth in xenografts displaying mutant, overexpressed, or autocrine stimulated EGFR, neither antibody inhibits the in vitro growth of cells expressing wtEGFR. In contrast, mAb806 completely inhibits the ligand-associated stimulation of cells expressing EGFR(C271A/C283A). Clearly, the binding of mAb806 and mAb175 to the wtEGFR requires the epitope to be exposed either during receptor activation, mutation, or overexpression. This mechanism suggests the possibility of generating antibodies to target other wild-type receptors on tumor cells.

Leveraging protein purification strategies in proteomics

The proteomic studies, although, tend to be analytical in nature, yet many strategies of preparative protein purification can be usefully employed in such studies. This review points out the importance of purification techniques which are capable of dealing with samples which are suspensions rather than clear solution, e.g. aqueous two phase partitioning, three phase partitioning, expanded bed chromatography, etc. The review also outlines the potential of non-chromatographic techniques in dealing with fractionation of proteomes. Separation protocols which can deal with post-translationally modified (PTM) proteins are also considered.

Photocleavable peptide hydrogel arrays for MALDI-TOF analysis of kinase activity

We have developed an acrylamide copolymerization strategy to immobilize acrylamide labeled peptides and proteins into a hydrogel surface and detect their modifications using MALDI-TOF mass spectrometry. Copolymerization into hydrogels is robust, compatible with "off-the-shelf" chemistry, and yields materials and surfaces that are stable to aqueous or organic solvents, drying, high or low temperature, high or low pH, oxidizing agents, sonication, mechanical contact, etc. The use of acrylamide hydrogels allows immobilization of substrates in a hydrated environment that can be used both as a biological reaction matrix and as a MALDI target. In our strategy, a substrate peptide was designed in a modular fashion to include both modification site and affinity domains. It was labeled with an acrylamide functionality using a generalized chemistry and covalently attached to the surface with a photocleavable linker, allowing for aggressive washing to remove any fouling, followed by selective release for MALDI-TOF analysis. Using this system we were able to analyze and compare v-Abl (truncated) and c-Abl (full-length) kinase activity on a peptide substrate with an affinity domain specific for the full-length kinase, observing excellent overall reproducibility in the extent of phosphorylation detected. This work serves as proof of principle for modular substrate design strategies for mass spectrometry-readable biosensors.