03/27/2025
By Irma Silva
The Kennedy College of Sciences, Department of Biological Sciences, invites you to attend a Masters Thesis defense by Alfredo Bongiorno on "The Role of Key Tropomyosin-Troponin T Interactions in Thin Filament Mediated Myocardial Regulation."
Date: Tuesday, April 8, 2025
Time: 2 - 4 p.m.
Location: Olsen Hall 114
Committee
Jeffrey Moore, Professor, Biological Sciences, UMass Lowell
Teresa Lee, Assist. Professor, Biological Sciences, UMass Lowell
Matthew Gage, Assoc. Professor, Chemistry, UMass Lowell
Abstract:
This study investigates the role of a key interaction between Tropomyosin (Tpm) and Troponin T (TnT) in the regulation of cardiac muscle contraction, with a particular focus on understanding hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM). Approximately three in every 500 individuals are born with these conditions, which are caused by mutations in genes that disrupt regulatory processes in the heart. HCM manifests as impaired relaxation during ventricular filling at low calcium levels, while DCM results from impaired contraction during ventricular emptying at high calcium levels (i.e., diastolic and systolic dysfunction for HCM and DCM, respectively). Mutations in genes encoding myocardial contractile proteins, particularly the thin filament (TF), play a central role in both conditions. The cardiac thin filament governs contraction by sensing intracellular calcium levels, with conformational changes occurring at a threshold of pCa 6, enabling myosin-actin cross-bridge cycling and thus muscle contraction. Mutations in actin, troponin (Tn) and tropomyosin (Tpm), especially in TnT, have been linked to these diseases. Despite the known association between TnT mutations and cardiomyopathies, detailed residue-specific information about TnT-Tpm interactions and their impact on heart muscle function remains unknown.
Building on recent Cryo-EM structures, we identified a key residue that we predict is crucial for the TnT-Tpm interface and hypothesized how it would affect muscle regulation when mutated. We hypothesized that the tyrosine 261 of Tpm1.1 interacts with R131 of TnT1, and therefore, engineered mutations in Tpm 1.1 at position Y261, specifically Y261E, Y261F, and Y261Q, would either enhance, diminish or maintain the interaction between TnT and Tpm. Our second hypothesis stated that mutations with reduced TnT-Tpm affinity would demonstrate enhanced calcium sensitivity. Using co-sedimentation assays and in vitro motility assays, we found that the aromatic ring of Y261 in Tpm 1.1 is essential for maintaining wild-type levels of affinity with TnT1. Our second hypothesis was supported by our findings demonstrating a role of Tpm-TnT interactions in both calcium sensitivity and cooperativity of muscle activation. All of the engineered mutations resulted in a reduced ability of Tpm to bind F-actin. Our F-actin to Tpm affinity results suggest that mutations in Tpm at Y261 propagate structural changes throughout the Tpm molecule. The most severe mutation, Y261E, leads to a dramatic increase in maximal muscle activation and a significant reduction in the cooperativity of muscle activation. These findings demonstrate the crucial role of Tpm-TnT interactions in regulating muscle contraction and how mutations in this interface disrupt the thin filament's ability to properly regulate muscle contraction. In summary, our study highlights the importance of specific interactions between Tropomyosin and Troponin T in their role of regulating cardiac muscle contraction.