The Role of Hydrophobic Interactions in the Formation of Functional Troponin and in the Ca²⁺ Regulation of Muscle Contraction

Abstract

Atomic atructure of troponin C (TnC) in complex with N-terminal fragment of troponin I (TnI_1-47) determined at 2.3 Å resolution revealed the compact globular conformation of the TnC molecule, which is likely to exist within the intact troponin (Tn). The TnI_1-47 long α-helix joins two domains of TnC by polar interaction, while its amphiphilic portion is tightly bound in the hydrophobic cleft of the C-domain of TnC through 38 van der Waals interactions. The model was proposed for another TnI amphiphilic α-helical segment, which binding/release to/from the regulatory N-domain of TnC would actually regulate the acto-myosin ATPase.