Comparative NMR analysis of collagen triple helix organization from N- to C-termini

The collagen triple helix consists of three supercoiled solvent-exposed polypeptide chains, and by dry weight it is the most abundant fold in mammalian tissues. Many factors affecting the structure and stability of collagen have been determined through the use of short synthetically prepared peptides, generally called collagen-mimetic peptides (CMPs). NMR (nuclear magnetic resonance spectroscopy) investigations into the molecular structure of CMPs have suffered from large amounts of signal overlap and degeneracy because of collagen's repetitive primary sequence, the close and symmetric packing of the three chains and the identical peptide sequences found in homotrimers. In this paper a peptide library is prepared in which a single isotopic (15)N-Gly label is moved sequentially along the peptide backbone. Our approach allows for a more explicit examination of local topology than available in past reports. This reveals larger regions of disorder at the C-terminus than previously detected by crystallographic or NMR studies, and here C-terminal fraying is seen to extend for six amino acids in a (POG)10 sequence. Furthermore, small sequence changes at the N-terminus greatly influence the degree of this localized disorder and may be useful in the future design of CMPs to maximize collagen's interstrand hydrogen bonding pattern. Our approach and data serves as a reference for future CMP characterizations to determine the quality and extent of folding.