title: Role of cardiac troponin I carboxy terminal mobile domain and linker sequence in regulating cardiac contraction.
abstract: Inhibition of striated muscle contraction at resting Ca(2+) depends on the C-terminal half of troponin I (TnI) in thin filaments. Much focus has been on a short inhibitory peptide (Ip) sequence within TnI, but structural studies and identification of disease-associated mutations broadened emphasis to include a larger mobile domain (Md) sequence at the C-terminus of TnI. For Md to function effectively in muscle relaxation, tight mechanical coupling to troponin's core-and thus tropomyosin-is presumably needed. We generated recombinant, human cardiac troponins containing one of two TnI constructs: either an 8-amino acid linker between Md and the rest of troponin (cTnILink8), or an Md deletion (cTnI1-163). Motility assays revealed that Ca(2+)-sensitivity of reconstituted thin filament sliding was markedly increased with cTnILink8 (∼0.9 pCa unit leftward shift of speed-pCa relation compared to WT), and increased further when Md was missing entirely (∼1.4 pCa unit shift). Cardiac Tn's ability to turn off filament sliding at diastolic Ca(2+) was mostly (61%), but not completely eliminated with cTnI1-163. TnI's Md is required for full inhibition of unloaded filament sliding, although other portions of troponin-presumably including Ip-are also necessary. We also confirm that TnI's Md is not responsible for superactivation of actomyosin cycling by troponin.
authors.affiliation: Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, OR, USA.
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Meyer
authors.affiliation: Department of Biological Science and Program in Molecular Biophysics, Florida State University, Tallahassee, FL, USA. Electronic address: chase@bio.fsu.edu.
authors.forename: P Bryant
authors.initials: PB
authors.lastname: Chase
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D000205:Actomyosin / Q000737:chemistry; D000818:Animals; D002118:Calcium / Q000737:chemistry; D006801:Humans; D009126:Muscle Relaxation / Q000187:drug effects; D018482:Muscle, Skeletal / Q000378:metabolism; D009154:Mutation; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism; D000072417:Protein Domains; D011817:Rabbits; D011994:Recombinant Proteins / Q000737:chemistry; D013314:Stress, Mechanical; D014335:Tropomyosin / Q000737:chemistry; D019210:Troponin I / Q000737:chemistry*
chemical_list: D000199:Actins; D011994:Recombinant Proteins; D014335:Tropomyosin; D019210:Troponin I; D000205:Actomyosin; D002118:Calcium
keywords: Calcium; Excitation-contraction coupling; Heart; In vitro motility assay; Thin filament; Unloaded filament sliding