Ionic Interventions That Alter the Association of Troponin C C-domain with the Thin Filaments of Vertebrate Striated Muscle.
From: Instituto de Bioquímica Médica, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Cidade Universitária, Rio de Janeiro, RJ 21941-590, Brazil.
Biochimica et biophysica acta
- Publish Date: Feb 2006
- ISSN: 0006-3002
- Volume: 1760
- Issue: 2
- Pages: 272-82
- Medium: Print
- Language: English
- Citation (JAMA): Sousa Valeria P, Pinto José R, Sorenson Martha M, et al. Ionic Interventions That Alter the Association of Troponin C C-domain with the Thin Filaments of Vertebrate Striated Muscle.. Biochim. Biophys. Acta Feb 2006;1760:272-82
Abstract
The regulatory complex of vertebrate skeletal muscle integrates information about cross-bridge binding, divalent cations and other intracellular ionic conditions to control activation of muscle contraction. Relatively little is known about the role of the troponin C (TnC) C-domain in the absence of Ca2+. Here, we use a standardized condition for measuring isometric tension in rabbit psoas skinned fibers to track TnC attachment and detachment in the absence of Ca2+ under different conditions of ionic strength, pH and MgATP. In the presence of MgATP and Mg2+, TnC detaches more readily and has a 1.5- to 2-fold lower affinity for the intact thin filament at pH 8 and 250 mM K+ than at pH 6 or in 30 mM K+; changes in affinity are fully reversible. The response to ionic strength is lost when Mg2+ and MgATP are absent, whereas the response to pH persists, suggesting that weaker electrostatic TnC-TnI-TnT interactions can be overridden by strongly bound cross-bridges. In solution, titration of a fluorescent C-domain mutant (F154W TnC) with Mg2+ reveals no significant changes in Mg2+ affinity with pH or ionic strength, suggesting that these parameters influence TnC binding by acting directly on electrostatic forces between TnC and TnI rather than by changing Mg2+ binding to C-domain sites III and IV.
Mesh Headings (Keywords): Animals, Chickens, Hydrogen-Ion Concentration, Magnesium, Muscle Fibers, Muscle, Skeletal, Osmolar Concentration, Protein Structure, Tertiary, Rabbits, Spectrometry, Fluorescence, Troponin C, Troponin I, Troponin T
Check for Full Text / PubMed Unique Identifier (PMID): 16300900
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