Effects of Calcium on the Stability of VWF-A2 Domain by Molecular Dynamics Simulation / 医用生物力学

ABSTRACT

Objective To investigate the effect of calcium on the stability of VWF-A2 domain. Methods The crystal structures of A2 (not containing calcium) and A2/Ca2+ (with calcium bound) were downloaded from protein data bank. For A2 domain, the conformational changes, unfolding pathway differences and the exposure degree variance of cleavage sites caused by calcium binding were observed and analyzed by steered Molecular Dynamics simulations under constant force. Results The unfolding pathway of A2 domain and exposure process of cleavage sites were force-dependent. Calcium binding did not affect the unfolding process of A2 in the early stage. As the conformational rearrangement of α3β4-loop reduced its localized dynamic properties, the movement among β1-β4-β5 strands was restrained, which suppressed its further unfolding to stay in the intermediate steady state and delayed the cleavage-site exposure. Conclusions Stretch force could induce β5 strand of A2 unfolding and the cleavage-site exposure, while calcium binding inhibited ADAMTS13 proteolysis efficiency through stabilizing A2 hydrophobic core and covering its cleavage sites. These results way help to understand how ADAMTS13 cleavages the VWF-A2 domain and regulates the hemostatic potential of VWF, and further provide useful guidance on the design of related anti-thrombus drugs.