title: Complexation and Calcium-Induced Conformational Changes in the Cardiac Troponin Complex Monitored by Hydrogen/Deuterium Exchange and FT-ICR Mass Spectrometry.
abstract: Cardiac muscle contraction is regulated by the heterotrimeric complex: troponin. We apply solution-phase hydrogen/deuterium exchange monitored by FT-ICR mass spectrometry to study the structural dynamics and the Ca-induced conformational changes of the cardiac isoform of troponin, by comparing H/D exchange rate constants for TnC alone, the binary TnC:TnI complex, and the ternary TnC:TnI:TnT complex for Ca-free and Ca-saturated states. The wide range of exchange rate constants indicates that the complexes possess both highly flexible and very rigid domains. Fast exchange rates were observed for the N-terminal extension of TnI (specific to the cardiac isoform), the DE linker in TnC alone, and the mobile domain of TnI. The slowest rates were for the IT coiled-coil that grants stability and stiffness to the complex. Ca(2+) binding to site II of the N-lobe of TnC induces short-range allosteric effects, mainly protection for the C-lobe of TnC that transmits long-range conformational changes that reach the IT coiled-coil and even TnT1. The present results corroborate prior X-ray crystallography and NMR interpretations and also illuminate domains that were not resolved or truncated in those experiments.
authors.affiliation: Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306.
authors.forename: George M
authors.initials: GM
authors.lastname: Bou-Assaf
authors.forename: Jean E
authors.initials: JE
authors.lastname: Chamoun
authors.forename: Mark R
authors.initials: MR
authors.lastname: Emmett
authors.forename: Piotr G
authors.initials: PG
authors.lastname: Fajer
authors.forename: Alan G
authors.initials: AG
authors.lastname: Marshall