Structural insights from (15)N relaxation data for an anisotropic collagen peptide

The degree of H bonding is thought to play an important role in defining collagen recognition sites or regions that contain disease-causing collagen mutations. For collagen model peptides, structure determination by standard NMR approaches is limited because of their rodlike anisotropic shape and repeating sequence. We demonstrate that (15)N relaxation NMR experiments and their dependence on rotational diffusion anisotropy can be used to obtain novel structural information about the orientation of the N-H bonds relative to the protein backbone in these rodlike systems. (15)N relaxation measurements on a triple-helical peptide that models a collagen sequence just C-terminal to the unique collagenase cleavage site indicated that the angle between the N-H bond vector and the diffusion tensor of the Gly residues needed to be readjusted. After the Gly amide protons were placed out of the C'-N-Calpha plane, the hydrogen-bond angles and distances were recalculated and shown to be closer to 180 degrees and shorter, respectively. The data suggest that deviations of the Gly amide protons from their standard positions arise from hydrogen-bonding effects and that these may impact the hydrogen-bond strengths in this collagen recognition region.