Structural Defects Induced by Malignant Mutations in the Regulatory Light Chain of Myosin

Abstract

The current study is aimed at providing insight into the structural defects underlying the development of malignant phenotypes induced by D166V and R58Q mutations in the regulatory light chain (RLC) of myosin. X-ray diffraction studies were carried out on the freshly skinned papillary muscle fibers from transgenic mutant vs. wild-type mice using the small angle instrument on the BioCAT beamline 18-D at the Advanced Photon Source. The fiber was immersed in relaxing solution and the X-ray measurements were made at two sarcomere lengths (SL), short (∼2.3 μm) and long (∼2.5 μm). At the short SL, we observed that the R58Q mutation caused a significant increase in the interfilament lattice spacing (d1,0) compared to Tg-WT while no change was observed for the D166V mutation. Interestingly, upon stretch to long SL, WT and R58Q showed a significantly decreased lattice spacing (by ∼1.5 nm) while the d1,0 in the D166V myocardium remained the same as measured at short SL. The lack of structural response to stretch observed for D166V may indicate a mutation induced increase in fiber stiffness. In support of this notion, measurements of passive force performed in glycerinated skinned papillary Tg-D166V fibers demonstrated significantly increased levels of passive tension at all points of stretch (10%, 20%, 30% and 40% of fiber length) indicating an elevated resistance to stretch in Tg-D166V compared to Tg-WT fibers. Our results suggest that the mutant-induced structural changes that most likely trigger pathological remodeling of the heart leading to FHC are different for both studied RLC mutations. Supported by AHA-10POST3420009 (PM), NIH- HL071778 (DSC), HL090786 (DSC), P41 GM103622-17 (TI)