From synthetic to doped collagen: design of new peptidomimetic molecules – COLD

Collagen is the most abundant protein in the animal kingdom. In human, type I collagen is the prevalent form among 28 different types, accounting for 90% of the skeletons and being also widespread all over the body. It has a fibrillar structure, which consists of several triple helices forming supertwisted right-handed microfibrils. Abnormalities in its structure are associated with several connective tissue diseases. Deciphering the parameters that stabilize the collagen fibrils could lead to a better understanding of these disorders. Collagen is also an important biomaterial because of its excellent thermal stability and its great mechanical strength. Fish, bovine or porcine collagen is readily available and has been used for tissue engineering, cosmetic surgery and drug delivery systems. However, it suffers from heterogeneity, potential immunogenicity, and loss of structural integrity during the isolation process. The heterologous production of collagen is made problematic by the difficulty of incorporating crucial post-translational modifications, and by the need to use complex expression systems. The development of novel and safer biomaterials is therefore a great economical challenge. This last decade, both the industry and the academia have been involved in the development of new collagen-related biomaterials. One common strategy consists in using Collagen Model Peptides (CMP) as collagen surrogates. CMPs are generally 15-45 residue long peptides that mimic the (Pro-Hyp-Gly)n collagen primary sequence, where Pro, Hyp and Gly are proline, (2S,4R)-4-hydroxyproline, and glycine residues, respectively. Under certain conditions, it has been shown that collagen-like triple helices are obtained, which undergo further supramolecular assembly. However, to date, the described synthetic collagen-mimetic fibrils still lack many characteristics of the intact collagen structure.
In the present project, we propose to design new peptidomimetics that are endowed with marked collagen properties (synthetic collagen). We do not claim to find “ready to use” compounds for biomaterials applications, but as a first step, a new generation of molecules giving promising results in vitro. Our approach will differ from other ongoing research for the following three reasons. Firstly, we will take full advantage of the unique structural properties of two non-natural amino acids that we recently described: CF3-pseudoprolines and beta,gamma-diamino acids. CF3-pseudoprolines were found to provide a very tight control of the thermodynamic features of the peptide chain. It is possible to preorganize the peptide backbone in a PolyProline II conformation (PPII) that is required to form the collagen triple helix. It thereby decreases the entropic cost for collagen folding. Regarding beta,gamma-diamino acids, the additional H-bond donor is expected to promote supramolecular assembly, as observed in our preliminary results. Moreover, the NMR structures of hybrid alpha,gamma-peptidomimetics incorporating beta,gamma-diamino consist in extended conformations that are very similar to the PPII helix, enforcing the relevance of these molecules in the collagen field. Secondly, we plan to explore the interactions occurring between the natural type I collagen and some of our designed molecules. It is expected that potent peptidomimetics will alter/stabilize the collagen phases (doped collagen). As a preliminary step, we plan to replace the intact collagen by shorter CMPs, which should allow the atomic level description of the peptidomimetic:collagen interactions. Thirdly, we will perform a multidisciplinary approach, combining organic chemistry, spectroscopies (CD, Liquid- and Solid-state NMR), microcalorimetry, molecular dynamics, optical and electron microscopies. The project is ambitious but the synergism between the different techniques should help us in obtaining an integrated view for a rational design of the new peptidomimetics.