Structural Studies of Triple-Helical Proteins

Univ Of Med/Dent Nj-R W Johnson Med Sch, Piscataway NJ

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Abstract

A peptide approach to a comprehensive understanding of the effect of amino acid sequence (Gly-X-Y)n on the stability, conformation, folding, dynamics and self-association of the normal and mutant collagen triple-helix is in progress. Our goals are to complete sequence-stability correlations at the molecular level; to develop peptides to model triple-helix self-association; and to pursue the disruption caused by Gly substitutions found in collagen diseases. Previous host-guest peptide studies established the triple-helix propensities of all 20 amino acids for the X and Y positions, and evaluation of molecular interactions within the triple-helix will be completed. These relationships between Gly-X-Y sequence and stability will be used to formulate predictions for the global stability of collagen model peptides and to relate local stability variations along collagen with ligand binding sites, microunfolding implicated in fibril formation, and the clinical severity of mutations. Calorimetric investigations are proposed to elaborate the mechanism of hydroxyproline stabilization of the triple-helix, and studies are proposed to further investigate the recently established sequence related modulation of triple-helix twist. An important goal is to establish a peptide system to model the self-association of triple-helices, since collagens function in supramolecular assemblies and some collagen mutations are pathological because of their influence on higher order structure. Strategies to design self-associating peptides will include pairs of oppositely charged residues to promote in register arrays and adaptation of sticky end and repeating pattern designs to form staggered arrays. Studies are proposed on peptide models of type I collagen mutations leading to a bone disease (osteogenesis imperfecta) and of type VII collagen mutations leading to a blistering skin disease (dystrophoic form of epidermolysis bullosa). The effect of the immediate sequence environment of the mutation and the identity of the residue replacing the Gly will be examined. Placing collagen structure, dynamics, and folding in a solid physicochemical framework through peptide studies will provide a context for understanding normal biological activities of selfassociation and binding, and for the changes occurring in many diseases affected by this abundant protein.