title: C-terminal truncation of cardiac troponin I causes divergent effects on ATPase and force: implications for the pathophysiology of myocardial stunning.
abstract: Myocardial stunning is a form of reversible myocardial ischemia/reperfusion injury associated with systolic and diastolic contractile dysfunction. In the isolated rat heart model, myocardial stunning is characterized by specific C-terminal proteolysis of the myofilament protein, troponin I (cTnI) that yields cTnI1-193. To determine the effect of this particular C-terminal truncation of cTnI, without the confounding factor of other stunning-induced protein modifications, a series of solution biochemical assays has been undertaken using the human homologue of mouse/rat cTnI1-193, cTnI1-192. Affinity chromatography and actin sedimentation experiments detected little, or no, difference between the binding of cTnI (cTnI1-209) and cTnI1-192 to actin-tropomyosin, troponin T, or troponin C. Both cTnI and cTnI1-192 inhibit the actin-tropomyosin-activated ATPase activity of myosin subfragment 1 (S1), and this inhibition is released by troponin C in the presence of Ca2+. However, cTnI1-192, when reconstituted as part of the troponin complex (cTn1-192), caused a 54+/-11% increase in the maximum Ca2+-activated actin-tropomyosin-S1 ATPase activity, compared with troponin reconstituted with cTnI (cTn). Furthermore, cTn1-192 increased Ca2+ sensitivity of both the actin-tropomyosin-activated S1 ATPase activity and the Ca2+-dependent sliding velocity of reconstituted thin filaments, in an in vitro motility assay, compared with cTn. In an in vitro force assay, the actin-tropomyosin filaments bearing cTn1-192 developed only 76+/-4% (P<0.001) of the force obtained with filaments composed of reconstituted cTn. We suggest that cTnI proteolysis may contribute to the pathophysiology of myocardial stunning by altering the Ca2+-sensing and chemomechanical properties of the myofilaments.
authors.affiliation: Department of Biochemistry , Queen's University, Kingston, Ontario, Canada.
authors.forename: D Brian
authors.initials: DB
authors.lastname: Foster
authors.forename: Teruo
authors.initials: T
authors.lastname: Noguchi
authors.forename: Peter
authors.initials: P
authors.lastname: VanBuren
authors.forename: Anne M
authors.initials: AM
authors.lastname: Murphy
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Van Eyk
mesh_terms: D000199:Actins / Q000737:chemistry / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism*; D002846:Chromatography, Affinity; D006801:Humans; D046911:Macromolecular Substances; D017682:Myocardial Stunning / Q000503:physiopathology*; D017384:Sequence Deletion; D013314:Stress, Mechanical; D014335:Tropomyosin / Q000737:chemistry / Q000378:metabolism; D019209:Troponin C / Q000737:chemistry / Q000378:metabolism; D019210:Troponin I / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020107:Troponin T / Q000737:chemistry / Q000378:metabolism; D014461:Ultracentrifugation
chemical_list: D000199:Actins; D046911:Macromolecular Substances; D014335:Tropomyosin; D019209:Troponin C; D019210:Troponin I; D020107:Troponin T; D000251:Adenosine Triphosphatases