10/01/2021
By Meaghan Barry

The Kennedy College of Science, Department of Biological Sciences, invites you to attend a Ph.D. proposal defense by Meaghan Barry on "Molecular mechanisms of troponin I-based regulation of cardiac muscle contraction."

Ph.D. Candidate: Meaghan E. Barry
Defense Date: Thursday, Oct. 7, 2021
Time: 11 a.m.
Location: Olsen Hall, room 503

Committee Chair (Advisor): Jeffrey Moore, Professor, Biological Sciences, UMass Lowell

Committee Members:

  • Matthew Gage, Associate Professor, Chemistry, UMass Lowell
  • Nicolai Konow, Assistant Professor, Biological Sciences, UMass Lowell
  • William Schmidt, Assistant Professor, Biology, Rivier University

Abstract:

Heart failure, the leading cause of death in the US, is often caused by genetic mutations in sarcomere proteins of the cardiac thin filament (TF). The primary regulator of cardiac muscle contraction, the TF consists primarily of F-actin, tropomyosin (Tpm), and the troponin complex (Tn), comprised of TnC, TnT, and TnI. Calcium binding to TnC propagates to induce a shift in Tpm, allowing for actomyosin interactions, which powers contraction with each heartbeat. While the general structure of the TF has been well characterized, vital regions of the communication pathway where Tn triggers Tpm movement remains unresolved. Specifically, helix 4 and the TnI C-terminus, thought to force Tpm in a position on actin to promote muscle relaxation, have only been determined at low resolution. Recent work from our collaborative team, using cryo-electron microscopy data coupled to computational chemistry, has provided insight to this region at molecular resolution. With this novel information, I hypothesize the predicted electrostatic interactions at helix 4, Tpm-E139 with TnI-R170 and K174, are vital for maintaining the blocked state (B-state), and with mutation-induced alterations, I will determine the importance of these molecular interactions to heart muscle regulation. Aim 1 will test the Tpm-TnI interaction by switching the charges on TnI (R170E/K174E) to test the effect on B-state stability through variations in TF activation (in-vitro motility) and Tpm-TnI affinity (co-sedimentation assays and surface plasmon resonance). My preliminary data of the disruptive Tpm-E139K mutation is consistent with my hypothesis, demonstrating the importance of these interactions, by revealing an increase in calcium sensitivity. Further, to test the predictive nature of our model, we propose to rescue the effects by creating analogous salt bridge stabilization in a double mutant system (TnI-R170E/K174E with Tpm-E139K). C-terminal residue S199, identified as a phosphorylation site in late-stage heart failure, is adjacent to Tpm acidic residue E98 in our model. Pseudo-phosphorylation of TnI(S199D) will test phosphorylation’s effect on TF regulation in aim 2, while testing the proximity to Tpm by introducing a potential salt-bridge interaction (Tpm-E98R) with TnI-S199D. Collectively, this study will provide a well-rounded picture of the molecular mechanism in which TnI regulates cardiac muscle contraction, while addressing how this complex system can lead to disease and heart failure.