Fig. 3:

Molecular kinetics and mechanism for strain-suppressed enzymatic degradation of collagen–I molecule within collagen fibrils. (A-i) Michaelis-Menten model states collagenase-collagen dissociation constant (K) increases with tensile strain on collagen fibrils and, (A-ii) collagen fibril degradation rate is suppressed with increasing tensile strain which is evident from (A-iii) respective degradation rates of collagen fibrils (mechanically strained or unstrained) when exposed to MMP-8, obtained using slopes of initial region of collagen conc. vs time curve (adopted from Flynn et al 2010 [77]) (B) Differences between MMP cleavage and BC-driven proteolysis. MMPs have smaller catalytic domains than BC and cut each α-chain of mechanically unloaded collagen molecule sequentially. The only vulnerable cleavage site of a partially unfolded α2-chain (for MMP-1, −8 & −13) is sequestered by mechanical strain. (C) BC cuts all α-chains of unstrained collagen molecule in parallel but the many cleavage sites are sequestered by mechanical strain.