Cardiomyopathic troponin mutations predominantly occur at its interface with actin and tropomyosin

Abstract

Reversible Ca2+ binding to troponin is the primary on-off switch of the contractile apparatus of striated muscles, including the heart. Dominant missense mutations in human cardiac troponin genes are among the causes of hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy. Structural understanding of troponin action has recently advanced considerably via electron microscopy and molecular dynamics studies of the thin filament. As a result, it is now possible to examine cardiomyopathy-inducing troponin mutations in thin-filament structural context, and from that to seek new insight into pathogenesis and into the troponin regulatory mechanism. We compiled from consortium reports a representative set of troponin mutation sites whose pathogenicity was determined using standardized clinical genetics criteria. Another set of sites, apparently tolerant of amino acid substitutions, was compiled from the gnomAD v2 database. Pathogenic substitutions occurred predominantly in the areas of troponin that contact actin or tropomyosin, including, but not limited to, two regions of newly proposed structure and long-known implication in cardiomyopathy: the C-terminal third of troponin I and a part of the troponin T N terminus. The pathogenic mutations were located in troponin regions that prevent contraction under low Ca2+ concentration conditions. These regions contribute to Ca2+-regulated steric hindrance of myosin by the combined effects of troponin and tropomyosin. Loss-of-function mutations within these parts of troponin result in loss of inhibition, consistent with the hypercontractile phenotype characteristic of HCM. Notably, pathogenic mutations are absent in our dataset from the Ca2+-binding, activation-producing troponin C (TnC) N-lobe, which controls contraction by a multi-faceted mechanism. Apparently benign mutations are also diminished in the TnC N-lobe, suggesting mutations are poorly tolerated in that critical domain.

Cardiac Troponins: Contemporary Biological Data and New Methods of Determination

“…Numerous genetic studies revealed a large number of mutations in genes encoding troponin proteins (for example, by the type of substitution or deletion of one or several nucleotides), which led to the replacement of the corresponding amino acids and disruption of the regulatory function of troponins, phenotypically manifested in the form of various contractile dysfunctions and cardiomyopathies. [3][4][5][6][7][8] The etiopathogenesis and clinical manifestations of such disorders are described in sufficient detail in several review papers. [6][7][8] The amino acid composition of the two proteins included in the troponin complex (cTnI and cTnT) of the cardiac muscle differs from the amino acid composition of these proteins localized in the troponin complex of skeletal muscle, while the amino acid composition of cTnC and skeletal troponin C are completely identical.…”

“…[3][4][5][6][7][8] The etiopathogenesis and clinical manifestations of such disorders are described in sufficient detail in several review papers. [6][7][8] The amino acid composition of the two proteins included in the troponin complex (cTnI and cTnT) of the cardiac muscle differs from the amino acid composition of these proteins localized in the troponin complex of skeletal muscle, while the amino acid composition of cTnC and skeletal troponin C are completely identical. 1,2,9 The main site of localization of cardiac-specific troponin proteins (cTnI, cTnT) is the myocardium, which allows their use as specific biomarkers for identification of cardiac muscle alteration.…”

“… 3–8 The etiopathogenesis and clinical manifestations of such disorders are described in sufficient detail in several review papers. 6–8 …”

Toward an understanding of myofibrillar function in health and disease

“…Based on their analyses, they propose that developing effective treatments for these disorders will greatly benefit from binning patient subpopulations based on common underlying biophysical mechanisms that drive the molecular disease pathogenesis. Tobacman and Cammarato (2021) hone in on the locations of pathogenic and non-pathogenic troponin mutations in a thin filament atomic model. They show that the large majority of pathogenic sites are in troponin regions that inhibit contraction via direct contacts with actin or tropomyosin.…”

Computational and biophysical determination of pathogenicity of variants of unknown significance in cardiac thin filament

“…To address the molecular component of this challenge, we have previously developed an atomistic model of the CTF that includes all protein components and regions. To our knowledge, this is the only full atomistic model and is critically important as one addresses mutations near “unstructured” regions not resolved in any previous experiment, where most variants arise ( 20 ). The full atomistic model has previously been used as a mechanistic probe to simulate structural and dynamic changes induced by mutations that are not addressable by experiment.…”