Prediction Modeling of the MYH6 R443P Variant in Hypoplastic Left Heart Syndrome
Authors: Kaiser Carl , Klestinski Keith , Patel Siddharth , Mitchell Michael , Stegeman Robert , Ledger Owen , Groppi Collin , Malloy Joseph , Smith Sean , Akbar Asad , Homberg Logan , Richardson Michael , Novotny Jacob 
Published: June 2021

Genetic variants in the alpha myosin heavy chain gene (MYH6; a‐MHC) are significantly enriched in Hypoplastic Left Heart Syndrome (HLHS), an anatomically and clinically severe form of Congenital Heart Disease (CHD). HLHS is characterized by atresia/stenosis of the aortic and mitral valves, and severe hypoplasia of the left ventricle and aorta. A novel variant resulting in an arginine to proline change (R443P) in the head domain of MYH6 was found to segregate with disease in a multigenerational family affected with HLHS and other forms of CHD.

a‐MHC is a contractile protein that is important in the developing heart. After birth a‐MHC is located mainly in the atria, while the beta isoform (b‐MHC), which is encoded by the MYH7 gene, is mainly located in the ventricles Variants in both isoforms have been previously associated with hypertrophic and dilated cardiomyopathy, a leading cause of sudden cardiac death in children and adults, as well as CHD. . The two isoforms have ~92% amino acid homology, yet have distinct functional characteristics. At the cellular level, more is known about how variants in MYH7 cause disease because the majority of the b‐MHC protein has been crystallized, while crystal structures have not been solved for any portions of the human a‐MHC protein.

The MUHS SMART team submitted two amino acid sequences from the MYH6 gene to I‐TASSER, a bioinformatics method for predicting three‐dimensional protein structure, in order to study the effect of the MYH6 R443P variant on protein structure and function. The first submission contained the wild‐type amino acid sequence, while the second contained the R443P variant. The predicted protein structures were 3‐D printed in order to visualize any structural differences between the wild‐type and variant. I‐TASSER results did not show a significant change in secondary structure but did predict altered ligand binding in the variant protein compared to wild‐type. The electrostatic interface changed from a positively charged, polar amino acid (arginine) to one with a neutral, non‐reactive side chain (proline).

The R443P variant occurs within the helix O domain, which lies between the actin binding domain and the ATP binding region, and contains subdomains responsible for binding numerous other proteins, as well as, hydrolyzing ATP during contraction. Normal function of myosin during each contraction of the heart requires that interactions with this region occur at the appropriate place and time. We hypothesize that altered binding properties of myosin heavy chain could lead to altered contractility, affecting the maximum shortening velocity and force during muscle contraction in the developing heart. Future research will focus on the mechanism that this variant has on the functionality of these domains as well as drug targeting therapies as a means to correct or remediate the impact of variants such as R443P.

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This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.