title: Drastic Ca2+ sensitization of myofilament associated with a small structural change in troponin I in inherited restrictive cardiomyopathy.
abstract: Six missense mutations in human cardiac troponin I (cTnI) were recently found to cause restrictive cardiomyopathy (RCM). We have bacterially expressed and purified these human cTnI mutants and examined their functional and structural consequences. Inserting the human cTnI into skinned cardiac muscle fibers showed that these mutations had much greater Ca2+-sensitizing effects on force generation than the cTnI mutations in hypertrophic cardiomyopathy (HCM). The mutation K178E in the second actin-tropomyosin (Tm) binding region showed a particularly potent Ca2+-sensitizing effect among the six RCM-causing mutations. Circular dichroism and nuclear magnetic resonance spectroscopy revealed that this mutation does not extensively affect the structure of the whole cTnI molecule, but induces an unexpectedly subtle change in the structure of a region around the mutated residue. The results indicate that the K178E mutation has a localized effect on a structure that is critical to the regulatory function of the second actin-Tm binding region of cTnI. The present study also suggests that both HCM and RCM involving cTnI mutations share a common feature of increased Ca2+ sensitivity of cardiac myofilament, but more severe change in Ca2+ sensitivity is associated with the clinical phenotype of RCM.
authors.affiliation: Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan.
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Yumoto
authors.forename: Qun-Wei
authors.initials: QW
authors.lastname: Lu
authors.forename: Sachio
authors.initials: S
authors.lastname: Morimoto
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Tanaka
authors.forename: Naoko
authors.initials: N
authors.lastname: Kono
authors.forename: Koji
authors.initials: K
authors.lastname: Nagata
authors.forename: Takao
authors.initials: T
authors.lastname: Ojima
authors.forename: Fumi
authors.initials: F
authors.lastname: Takahashi-Yanaga
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Miwa
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Sasaguri
authors.forename: Kiyoyoshi
authors.initials: K
authors.lastname: Nishita
authors.forename: Masaru
authors.initials: M
authors.lastname: Tanokura
authors.forename: Iwao
authors.initials: I
authors.lastname: Ohtsuki
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects* / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000737:chemistry / Q000494:pharmacology*; D002313:Cardiomyopathy, Restrictive / Q000235:genetics / Q000378:metabolism*; D002413:Cations, Divalent / Q000737:chemistry; D002942:Circular Dichroism; D006801:Humans; D008239:Lysine / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D019210:Troponin I / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D002413:Cations, Divalent; D019210:Troponin I; D008239:Lysine; D002118:Calcium