A Molecular Map of the Interactions between Titin and Myosin‐Binding Protein C

Abstract

The thick filaments of vertebrate striated muscles contain with myosin a number of accessory proteins of the intracellular immunoglobulin superfamily, which are localized in a distinct pattern of stripes 43 nm apart. The specific localization of these proteins is believed to be due partly to their interaction with the giant muscle protein titin (also called connectin), which spans the entire sarcomere and may act as a molecular ruler. We have used recombinant fragments of titin covering the thick filament region to investigate their interaction with myosin-binding protein C (MyBP-C) from skeletal and cardiac muscle. The interaction of titin and MyBP-C is directed by a subset of titin immunoglobulin domains that are specific for the C-region of the thick filament, supporting the ruler hypothesis for the myosin-binding proteins. The interaction of recombinant titin with overlapping fragments of human cardiac MyBP-C maps the titinbinding site within the C-terminal region, which is deleted in patients suffering from the chromosome-1 1-associated form of familial hypertrophic cardiomyopathy. This disorder is therefore likely to be the result of thick-filament misassembly by abolishing the ternary interaction of titin, inyosin and MyBP-C.

Isoform-specific Interaction of the Myosin-binding Proteins (MyBPs) with Skeletal and Cardiac Myosin Is a Property of the C-terminal Immunoglobulin Domain

“…Available data cannot distinguish between these possibilities. Evidence exists that titin binds to MyBP-C and that this binding may occur within the last four domains of the MyBP (49). It is likely that titin forms a trimeric complex with myosin and MyBP-C, thereby facilitating and organizing the binding of MyBP-C to native myosin filaments.…”

“…The three adjacent motifs (motifs 7, 8, and 9) are also required for proper targeting of MyBP-C to the C-zone of the sarcomere. Because these latter modules appear to bind titin (36,49), it seems likely that insertion of MyBP-C into its native sites in the A-band requires the cooperative interaction of myosin, titin, and the MyBP. Thus, MyBP-H and MyBP-C could compete for binding to myosin, but their distinctive interactions with titin would modify their insertion in the sarcomere.…”

Cardiac myosin binding protein-C modulates actomyosin binding and kinetics in the in vitro motility assay

“…The protein consists of 11 domains (C0-C10), 8 immunoglobulin I-like and 3 fibronectin type 3 motifs, with putative binding of specific domains to the myosin tail (domain C10) [1], titin (domains C8-C10) [2], myosin sub-fragment 2 (S2, domains C1-C2) [3,4], and actin (domains C0-C1) [5,6]. Furthermore, while sedimentation studies indicate that cMyBP-C does not bind to myosin subfragment 1 (S1) [3], the C0-C1 domains may interact with the myosin head and affect contractile function [7,8].…”

Molecular genetics of familial hypertrophic cardiomyopathy (FHC)

“…In a majority of the cases, the mutation results in the formation of a truncated protein, which may lose the ability to bind to the myosin heavy chain (Bonne et al 1995;Freiburg and Gautel 1996;Okagi et al 1993). A few missense mutations have also been identified in this gene, including a study on a South-African family (Moolman-Smook et al 1998).…”