Nonuniform Curvature and Bending Rigidity of Adsorbed Collagen Molecules in Aqueous Solution.

Collagen, the most abundant protein in mammals, plays a key role in tissue formation and mechanics due to its triple-helix structure. We used atomic force microscopy to study individual type-I and type-III human collagen molecules adsorbed on smooth mica surfaces from low-salt, near-neutral aqueous solutions. Statistical analysis of their two-dimensional contours revealed nonuniform curvature in both collagen types, which persisted after surface drying and molecular dehydration, owing to robust collagen-mica adsorption. In addition, the angle between tangent vectors at the ends of molecular segments followed a non-Gaussian probability distribution, indicative of nonequilibrium quenching of fluctuations upon adsorption to mica. These results suggest that collagen either possesses an intrinsic three-dimensional curvature in solution or acquires a two-dimensional curvature upon adsorption. The first scenario has implications for the self-assembly and elasticity of collagen fibrils, whereas the second has implications in biomaterial design and tissue-engineering strategies.