title: Redox state of troponin C cysteine in the D/E helix alters the C-domain affinity for the thin filament of vertebrate striated muscle.
abstract: BACKGROUND
  Despite a broad spectrum of structural studies, it is not yet clear whether the D/E helix of troponin C (TnC) contributes to the interaction of TnC with troponin I (TnI). Redox modifications at Cys 98 in the D/E helix were explored for clues to TnC binding to the thin filament off-state, using recombinant wild-type TnC and an engineered mutant without Cys (Cys98Leu).
  
  
  METHODS
  Recombinant proteins and rabbit psoas skinned fibres were reduced with dithiothreitol (DTT) and variously recombined. Changes in affinity of reduced or oxidised TnC for the thin filament were evaluated via TnC binding and dissociation, using a standardized test for maximal force as an index of fibre TnC content.
  
  
  RESULTS
  All oxidation and reduction effects observed were reversible and led to changes in TnC content. Oxidation (H(2)O(2)) reduced TnC affinity for the filament; reduction (DTT) increased it. Reducing other fibre proteins had no effect. Binding of the Cys-less TnC mutant was not altered by DTT, nor was dissociation of wild-type TnC from reconstituted hybrids (skeletal TnC in cardiac trabeculae). Thus when Cys 98 in the D/E helix of TnC is fully reduced, its binding affinity for the thin filament of skeletal muscle is enhanced and helps to anchor it to the filament.
  
  
  CONCLUSIONS
  Signal transmission between TnC and the other proteins of the regulatory complex is sensitive to the redox state of Cys 98.
authors.affiliation: Instituto de Bioquímica Médica, Centro de Ciências da Saúde, Universidale federal do Rio de Janeiro, Cidale Universitária, Rio de Janeiro, Brazil. jpinto1@med.miami.edu
authors.forename: José Renato
authors.initials: JR
authors.lastname: Pinto
authors.forename: Valeria Pereira
authors.initials: VP
authors.lastname: de Sousa
authors.forename: Martha M
authors.initials: MM
authors.lastname: Sorenson
mesh_terms: D000818:Animals; D002645:Chickens; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism*; D004229:Dithiothreitol / Q000378:metabolism; D054792:Muscle, Striated / Q000378:metabolism*; D010084:Oxidation-Reduction; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011817:Rabbits; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D019209:Troponin C / Q000737:chemistry / Q000378:metabolism*; D019210:Troponin I / Q000378:metabolism; D020107:Troponin T / Q000378:metabolism; D014714:Vertebrates / Q000378:metabolism*
chemical_list: D011994:Recombinant Proteins; D019209:Troponin C; D019210:Troponin I; D020107:Troponin T; D003545:Cysteine; D004229:Dithiothreitol