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Investigation of labeled amino acid side-chain motion in collagen using 13C nuclear magnetic resonance

1980; Elsevier BV; Volume: 138; Issue: 2 Linguagem: Inglês

10.1016/0022-2836(80)90286-7

1089-8638

Lynn W. Jelinski, Dennis A. Torchia,

Bone health and osteoporosis research

13C1H double magnetic resonance was used to study the interactions and mobility of certain amino acid side-chains of collagen. Samples of collagen, labeled with [3-13C]alanine (a small hydrophobic amino acid), [methyl-13C]-methionine (a large hydrophobic), [6-13C]lysine (positively charged at physiological pH), and [5-13C]glutamic acid (negatively charged), were prepared via chick calvaria culture. 13C linewidths, lineshapes, NOE† values, and T1 values were measured for each sample as fibrils and as native (helical) material in solution. The measured T1 and NOE values for [3-13C]alanine-labeled collagen in solution, in conjunction with an ellipsoid model for collagen, indicate that the methyl rotation rate is 2 × 1010 s−1 and that the overall rate of diffusion about the long axis is 4× 106 s−1. These values agree with values for model compounds which undergo internal methyl rotation (Lyerla & Horikawa, 1976) and with previous n.m.r. measurements of the rate of rotational diffusion of backbone ([1-13C]- and [2-13C]glycine)-labeled collagen (Jelinski & Torchia, 1979). In addition, the n.m.r. data indicate that the terminal carbons of lysine, methionine and glutamic acid in labeled collagen (both in solution and as fibrils) are characterized by reorientation rates of approximately 109 to 1010 s−1. Taken together, the n.m.r. data provide strong evidence that the contact regions between the helices in collagen fibrils are fluid and that there is not a unique set of interactions between amino acid side-chains. In this respect, these n.m.r. results support current concepts of globular protein structure which suggest that a variety of conformations, in dynamic equilibrium, are responsible for the structure and function of proteins.