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. 2020 Jan 27;141(10):828–842. doi: 10.1161/CIRCULATIONAHA.119.042339

Figure 2.

Figure 2.

Destabilization of the interacting heads motif (IHM) by pathogenic HCM variants alters the proportion of myosins in the SRX and DRX conformations in mouse myocardium and human iPSC-CMs. A, Depiction of the functional domains of myosin, subunit 1 (S1), subunit 2 (S2), and light meromyosin (LMM), and the location of human MYH7 variants in patients with HCM: pathogenic variants (red), variants of unknown significance (VUS) that alter IHM residues (VUS IHM+, orange), and variants that alter residues outside the IHM (VUS IHM–, blue). B, The Protein Data Bank 5TBY model showing relaxed paired myosin heads, one with the ATP binding site blocked (olive) or accessible (green). The associated essential light chains (brown and purple), and regulatory light chains (dark blue and blue) are shown. Residues involved in the myosin IHM are depicted as a ribbon, with the location of 3 HCM pathogenic missense variants MYH7R403Q/+ (orange), MYH7V606M/+ (magenta), and MYH7R719W/+ (green). C, The same model shown in B and depicting the 3 HCM pathogenic missense variants (red), 2 VUS IHM+ (orange), and one VUS IHM– (blue). Two other VUS IHM– studied here are not visible in this projection. D and E, Proportion of myosin heads in DRX and SRX conformations in WT, Myh6403/+, Myh6606/+, and Myh6719/+ in 8-week-old mouse LV myocardium, in the presence or absence of 0.3 μmol/L MYK-461 as indicated. (See also Figure I in the online-only Data Supplement). F and G, Proportion of myosin heads in DRX and SRX conformations in WT, MYH7403/+, MYH7606/+, and MYH7719/+ iPSC-CMs in the presence or absence of 0.3 μmol/L MYK-461 as indicated. Data are from 3 independent heart tissues or differentiations of iPSC-CMs and are presented as means±SEM. Significance was tested by 1-way ANOVA and post hoc Bonferroni corrections for significances are denoted in the figure. Significances are reported in relation to WT values; bars encompassing significance values indicate that statistical significance is shared among these samples. DRX indicates disordered relaxed state conformation of myosin molecule; HCM, hypertrophic cardiomyopathy; iPSC-CMs, isogenic cardiomyocytes derived from induced pluripotent stem cells; NS, not significant; SRX, super relaxed state conformation of myosin molecule; and WT, wild type cardiomyocytes.