Structural, Functional, and Evolutionary Implications of a Histidine Moieity in Cardiac Troponin I.

Cardiovascular Physiology;Chordate Evolution;Molecular Modeling;Physiology;Science;Molecular and Integrative Physiology

Palpant, NathanSchwartz, Jessica ;

University of Michigan

关键词: Cardiovascular Physiology;    Chordate Evolution;    Molecular Modeling;    Physiology;    Science;    Molecular and Integrative Physiology;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/64822/npalpant_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Regulation of cardiac output is mediated by intrinsic and extrinsic factors that modulate the rhythmic transitions between contraction (systole) and relaxation (diastole). At the level of cardiac myofilaments, the troponin complex (troponin I (TnI), troponin C (TnC), and troponin T (TnT)) is the allosteric regulatory unit that controls the transition between active and inactive actomyosin cross-bridges. This is accomplished by the C-terminal switch arm of TnI toggling between actin during diastole and cTnC during systole in a calcium-dependent manner. These studies elucidate new knowledge regarding the structural, functional, and evolutionary implications of a histidine residue in the switch arm of troponin I. Molecular modeling of TnI isoforms and large scale bioinformatics analysis of chordate phylogenies were used to study the evolution of the cardiac troponin complex. At the molecular level, a single histidine to alanine substitution in the cTnI switch arm was the most effective mechanism for decreasing the binding free energy at the regulatory interface of TnI and TnC. Evidence suggests that this single amino acid substitution increases the intrinsic relaxation potential of the cTn complex enhancing diastolic performance to meet mammalian lusitropic demands. A histidine button in TnI is known to provide a therapeutic basis for pH responsive titratable inotropy in response to various cardiac stresses. As such, the physiological implications of a histidine button in mammalian cardiac TnI (cTnI A164H) were studied. Whole organ in vivo cardiac hemodynamic analysis shows that cTnI A164H Tg mice protect cardiac function from age-induced cardiomyopathy. Furthermore, cTnI A164H Tg hearts sustain cardiac performance during severe hypercapnic acidosis compared to complete pump failure with 100% mortality observed in control mice. In situ and in silico site-directed protein mutagenesis, in vitro cellular biophysics, and atomic resolution molecular dynamics simulations were used to analyze the therapeutic basis for a histidine button in cTnI. Evidence suggests that differential ionization of histidine mediates the titratable inotropy observed in myofilaments containing cTnI A164H.