Development of a novel oligomerization process to access bio-inspired and functional repeat protein mimics – REPEAT

Repeats of amino acid sequences frequently observed in protein structures are often associated with important physical or biological functions. Logically, producing such domains is an appealing strategy for engineering minimal protein mimics endowed with desired properties. In this context, the goal of the REPEAT project is to develop an innovative synthetic method that give access to tandem repeat sequences of amino acids by the oligomerization of peptide monomers. This approach is based on a chemical device recently discovered in the CBF team that enables the self-concatenation of a same unprotected peptide segment in water under extremely mild conditions, via a series of spontaneous and chemoselective chemical ligations. Having established the principle of assembling peptide segments by oligomerization on model compounds, we want to optimize the process, either in solution or on a water-compatible solid support, and explore its mechanism, to make this method a powerful and easy-to-use tool in the area of protein chemical synthesis. For this purpose, we will firstly investigate the effect of the reaction conditions on the average length and the dispersity of polypeptide mixtures produced by oligomerization. We will also perform structure/activity relationship studies to highlight the key parameters that govern the reactivity of the peptide monomer. With the aim of increasing the diversity of tandem repeat domains accessible by oligomerization, various post-oligomerization treatments will then be tested on model oligomers. Finally, we plan to extract from all the collected data a reliable kinetic model that will be used as a predictive tool for other polymerization systems. Once developed on model peptides, we will illustrate the synthetic utility of the oligomerization process for accessing potent mimics of natural antifreeze proteins (AFP). Secreted by a large variety of organisms living in cold environments to protect them from cryoinjuries, AFPs have promising applications in the diverse areas that are confronted to the control of ice-crystals growth, such as cryopreservation, food industry or anti-icing materials and are therefore valuable targets. All the synthetic advantages provided by the oligomerization will be combined to assemble in first instance the tandem repeat sequences that mimic the antifreeze glycoproteins produced by antartic fishes. More challenging in terms of design and synthesis is the second target, i.e., the family of hyperactive ß helices produced by Tenebrio molitor beetle (TmAFP). TmAFPs are made of highly similar but not identical repetitive motifs. Therefore, synthesizing TmAFP analogues by peptide oligomerization requires to use a consensus sequence for the monomer. To be active, TmAFP mimics must also adopt the repetitive disulfide bridge pattern that stabilize the 3D-structure of this protein family. To evaluate the antifreeze properties of the synthesized AFP mimics, we plan to measure the thermal hysteresis, i.e., the depression of the water freezing point induced by the presence of the protein. This expertise is rare in France and is brought by the LIEC team. Following this strategy, it will become possible to quickly evolve the sequences of AFPs, especially in terms of size, for accessing potent analogues. Considering the diversity of natural AFPs and more generally of proteins with repetitive motifs, this technology is an efficient tool to create a library of bio-inspired scaffolds that have attractive applications in material sciences or in chemical biology.