journal.pone.0058313.pdf (2.69 MB)
Calcium Induced Regulation of Skeletal Troponin — Computational Insights from Molecular Dynamics Simulations
journal contributionposted on 2014-01-03, 00:00 authored by Georgi Z. Genchev, Tomoyoshi Kobayashi, Hui Lu
The interaction between calcium and the regulatory site(s) of striated muscle regulatory protein troponin switches on and off muscle contraction. In skeletal troponin binding of calcium to sites I and II of the TnC subunit results in a set of structural changes in the troponin complex, displaces tropomyosin along the actin filament and allows myosin-actin interaction to produce mechanical force. In this study, we used molecular dynamics simulations to characterize the calcium dependent dynamics of the fast skeletal troponin molecule and its TnC subunit in the calcium saturated and depleted states. We focused on the N-lobe and on describing the atomic level events that take place subsequent to removal of the calcium ion from the regulatory sites I and II. A main structural event - a closure of the A/B helix hydrophobic pocket results from the integrated effect of the following conformational changes: the breakage of H-bond interactions between the backbone nitrogen atoms of the residues at positions 2, 9 and sidechain oxygen atoms of the residue at position 12 (N2-OE12/N9-OE12) in sites I and II; expansion of sites I and II and increased site II N-terminal end-segment flexibility; strengthening of the bsheet scaffold; and the subsequent re-packing of the N-lobe hydrophobic residues. Additionally, the calcium release allows the N-lobe to rotate relative to the rest of the Tn molecule. Based on the findings presented herein we propose a novel model of skeletal thin filament regulation.
This work is supported by the National Science Foundation through XSEDE resources provided by TACC-Lonestar (TG-MCB090005), and R01HL082923 and T32HL007692 from the National Institutes of Health U.S.A.
Publisher Statement© 2013 Genchev et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. © 2013 by Public Library of Science, PLoS ONE