title: Heme binding to calmodulin, troponin C, and parvalbumin, as a probe of calcium-dependent conformational changes.
abstract: Heme-CO binds to the active (calcium-bound) form of calmodulin (CaM), but not to the inactive form. Despite a similarity in structure of another calcium-binding protein, skeletal muscle troponin C, both the affinity and the spectral red-shift of the absorption of the heme group are greatly decreased for troponin C relative to calmodulin. Parvalbumin, another calcium-binding protein, shows a twofold greater affinity for heme-CO relative to CaM. Unlike calmodulin and troponin C, the affinity of parvalbumin for heme-CO is even greater in the absence of calcium. The affinity of the tryptic and thrombic fragments of CaM for heme-CO are decreased relative to the entire calmodulin. The binding of heme-CO is specific as demonstrated by the discrimination of the calmodulin, troponin C, and parvalbumin pockets. The interaction of heme-CO with active (calcium-bound) CaM is rapid (ms) as determined by stopped flow measurements. No difference in kinetics was observed for mixing inactive (calcium free) CaM with a solution of [heme-CO plus calcium], indicating that the calcium-binding step and subsequent change in protein conformation are rapid.
authors.affiliation: INSERM U299, Hôpital de Bicêtre, France.
authors.forename: E
authors.initials: E
authors.lastname: Leclerc
authors.forename: L
authors.initials: L
authors.lastname: Leclerc
authors.forename: R
authors.initials: R
authors.lastname: Cassoly
authors.forename: E
authors.initials: E
authors.lastname: der Terrossian
authors.forename: H
authors.initials: H
authors.lastname: Wajcman
authors.forename: C
authors.initials: C
authors.lastname: Poyart
authors.forename: M C
authors.initials: MC
authors.lastname: Marden
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism*; D002248:Carbon Monoxide; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D006418:Heme / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins; D007700:Kinetics; D009132:Muscles / Q000378:metabolism; D010320:Parvalbumins / Q000737:chemistry / Q000378:metabolism*; D010446:Peptide Fragments / Q000302:isolation & purification; D010455:Peptides; D011485:Protein Binding; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D014336:Troponin / Q000737:chemistry / Q000378:metabolism*; D019209:Troponin C; D014862:Wasp Venoms / Q000378:metabolism
chemical_list: D002147:Calmodulin; D036341:Intercellular Signaling Peptides and Proteins; D010320:Parvalbumins; D010446:Peptide Fragments; D010455:Peptides; D014336:Troponin; D019209:Troponin C; D014862:Wasp Venoms; D006418:Heme; C037500:mastoparan; D002248:Carbon Monoxide; D002118:Calcium