The interchain disulfide cross-linking of tropomyosin alters its regulatory properties and interaction with actin filament

Abstract

Tropomyosin (Tpm) is an α-helical coiled-coil actin-binding protein that plays a key role in the Ca²⁺-regulated contraction of striated muscles. Two chains of Tpm can be cross-linked by formation of a disulfide bond between Cys-190 residues. Normally, the SH-groups of these residues in cardiac muscle are in reduced state but in heart pathologies the interchain cross-linking of Tpm was shown to occur. Previous studies have shown that this cross-linking increases the thermal stability of the C-terminal part of the Tpm molecule. However it was unclear how this affects its functional properties. In the current work, we studied functional features of cross-linked Tpm at the level of isolated proteins. The results have shown that the cross-linking greatly decreases affinity of Tpm for F-actin and stability of the Tpm-F-actin complex. It also increases sliding velocity of regulated thin filaments in an in vitro motility assay. This last effect was mostly pronounced when cardiac isoforms of myosin and troponin were used instead of skeletal ones. The results indicate that cross-linking significantly affects properties of Tpm and actin-myosin interaction and can explain, at least partly, the role of the interchain disulfide cross-linking of cardiac Tpm in human heart diseases.

Keywords: Actin; Ca(2+)-regulation of muscle contraction; Disulfide cross-linking; In vitro motility assay; Tropomyosin.