Biophysical Society Thematic Meeting | Canterbury 2023

Towards a More Perfect Union: Multi-Scale Models of Muscle and Their Experimental Validation

Poster Abstracts

12-POS Board 12 POINT MUTATIONS AT THE SAME RESIDUE IN BETA MYOSIN HEAVY CHAIN LEAD TO DISTINCT DISEASES AND MOLECULAR PHENOTYPES Sarah J Lehman 1 ; Artur Meller 2 ; Jeffrey M Lotthammer 2 ; Shahlo O Solieva 4 ; Stephen J Langer 1 ; Michael J Greenberg 2 ; Jil C Tardiff 3 ; Gregory R Bowman 4 ; Leslie A Leinwand 1 ; 1 University of Colorado, Molecular, Cellular, and Developmental Biology, Boulder, CO, USA 2 Washington University, Department of Biochemistry and Molecular Biophysics, St. Louis, MO, USA 3 University of Arizona, Department of Biomedical Engineering, Tucson, AZ, USA 4 University of Pennsylvania, Department of Biochemistry and Biophysics, Philadelphia, PA, USA A frequently described phenomenon in genetic cardiomyopathies is how similar mutations in a single protein can lead to distinct clinical phenotypes. One example is described by two missense mutations in β - myosin heavy chain (β -MyHC) that have been linked to hypertrophic cardiomyopathy (HCM) (Ile467Val, I467V) and left ventricular non-compaction (LVNC) (Ile467Thr, I467T). To investigate how these mutations lead to different pathologies, we studied the molecular effects of each mutation using recombinant human β -MyHC Subfragment 1 (S1) in in vitro assays. LVNC-I467T S1 exhibited similar chemomechanical function to the HCM I467V S1 mutation, including unchanged ATPase activity (1.7±0.2/second, 1.7±0.3/second, β WT S1: 1.7±0.1/second) and enhanced actin velocity (1.4±0 .1/second, 2.5±0.3/second, β -WT S1: 3.0±0.2/second). LVNC-I467T showed a significant increase in the super-relaxed (SRX) state of myosin (93±4%) compared to both WT and the HCM-I467V mutant (16±4%, 10±2%, respectively). We conducted molecular dynamics simulations to explore how the LVNC-I467T mutation affects myosin dynamics in the pre-powerstroke state. Our simulations suggest I467T allosterically disrupts interactions between ADP and the nucleotide-binding pocket by breaking bonds between residues that stabilize ADP in the active site, leading to a weaker binding and a predicted increase in ADP release rate. This predicted ADP increased release rate may underlie the enhanced actin velocity measured in LVNC-I467T. Moreover, the unchanged ATPase activity of LVNC-I467T likely results from increased ADP release coupled to stabilization of the SRX state of myosin. This uncoupled chemomechanical function may initiate contractile dysregulation that triggers a distinct signaling pathway that progresses the LVNC-like phenotype. Alternatively, HCM-I467V variant exhibited a more predicted “gain of function” phenotype. Together, our analyses suggest that phenotypic complexity originates at the molecular level and is critical to understand disease progression and develop therapies.

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