A HIGH-RESOLUTION N-15 SOLID-STATE NMR-STUDY OF COLLAGEN AND RELATED POLYPEPTIDES - THE EFFECT OF HYDRATION ON FORMATION OF INTERCHAIN HYDROGEN-BONDS AS THE PRIMARY SOURCE OF STABILITY OF THE COLLAGEN-TYPE TRIPLE-HELIX

High-resolution solid-state N-15-NMR was used to clarify the effect of hydration on the stability of the coiled-coil triple-helix conformation of Gly-X(aa)-Y-aa repeating units in collagen and the collagen-like polypeptides, (Pro-Ala-Gly)(n) and (Pro-Pro-Gly)(10), because the stability is thought to be related to the presence of (Gly)NH...O=C(X(aa) or Pro) hydrogen bonds. The N-15-NMR signals of these samples were narrowed upon hydration, mainly due to hydration-induced conformational change or rearrangement of the repeating units. In particular, the N-15 chemical shifts of the Gly N-H group and the high-field (low-frequency) shoulder peak of Pro nitrogen signals in (Pro-Pro-Gly)(10) were shifted downfield (4.9 ppm and 6.8 ppm, respectively) with increasing relative humidity, while the corresponding peaks for collagen and (Pro-Ala-Gly)(n) were unchanged and close to the N-15 Shift of (Pro-Pro-Gly)(10) in the hydrated state. Such downfield shifts are consistent with the formation of N-H...O=C hydrogen bonds. In agreement with the NMR results, it was found that the (Gly)NH...O=C (X(aa) or Pro) hydrogen bonds are retained in dehydrated collagen fibrils but not in partially dehydrated (Pro-Pro-Gly)(10). No evidence was obtained for the partial formation of the 3(1) helix form (Pro)(n) or (Gly)(n) either under hydrated or dehydrated conditions. It is concluded that the Gly N-15 chemical shift is a very sensitive probe for studying supercoiling in collagen and collagenlike polypeptides.