Phenotypic effects of Ehlers-Danlos syndrome-associated mutation on the FnIII domain of tenascin-X.

Tenascin-X (TNX) is an extracellular matrix (ECM) protein and interacts with a wide variety of mols. in the ECM as well as on the membrane. Deficiency of TNX causes a recessive form of Ehlers-Danlos syndrome (EDS) characterized by hyperelastic and fragile skin, easy bruising, and hypermobile joints. Three point mutations in TNX gene were found to be assocd. with hypermobility type EDS and one of such mutations is the V1195M mutation at the 7th fibronectin Type III domain (TNXfn7). To help elucidate the underlying mol. mechanism connecting this mutation to EDS, here we combined homol. modeling, chem. denaturation, single mol. at. force microscopy, and mol. dynamics (MD) simulation techniques to investigate the phenotypic effects of V1195M on TNXfn7. We found that the V1195M mutation does not alter the three-dimensional structure of TNXfn7 and had only mild destabilization effects on the thermodn. and mech. stability of TNXfn7. However, MD simulations revealed that the mutation V1195M significantly alters the flexibility of the C’E loop of TNXfn7. As loops play important roles in protein-protein and protein-ligand interactions, we hypothesize that the decreased loop flexibility by V1195M mutation may affect the binding of TNX to ECM mols. and thus adversely affect collagen deposition and fibrillogenesis. Our results may provide new insights in understanding the mol. basis for the pathogenesis of V1195M-resulted EDS. [on SciFinder(R)]