4Ca2+.troponin C forms dimers in solution at neutral pH that dissociate upon binding various peptides : small-angle X-ray scattering studies of peptide-induced structural changes

• Published in: Biochemistry (Easton) Vol. 31; no. 46; pp. 11326 - 11334
• Main Authors: BLECHNER, S. L, OLAH, G. A, STRYNADKA, N. C. J, HODGES, R. S, TREWHELLA, J
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 24-11-1992
• Subjects: Amino Acid Sequence; Analytical, structural and metabolic biochemistry; Animals; Biological and medical sciences; Calcium - chemistry; Cations, Divalent; Contractile proteins; Fundamental and applied biological sciences. Psychology; Holoproteins; Hydrogen-Ion Concentration; Melitten - metabolism; Molecular Sequence Data; Muscles - chemistry; Peptides; Proteins; Rabbits; Scattering, Radiation; Troponin - chemistry; Troponin - metabolism; Troponin C; Wasp Venoms - metabolism; X-Rays; Ligand binding; Vertebrata; Troponin; Mammalia; Melittin; Solution structure; Conformational dynamics; Contractile protein; Rabbit; Lagomorpha; Striated muscle; Induced conformation
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00161a010

Small-angle X-ray scattering data have been measured for rabbit skeletal muscle troponin C and its complexes with the venom peptides melittin and mastoparan as well as synthetic peptides based on regions of the troponin I sequence implicated in troponin C binding. At the neutral pH used in this study (pH 6.8), troponin C shows a tendency to form dimers in the presence of 4 mol equiv of Ca2+, but is monomeric in solution when 2 or less mol equiv of Ca2+ is present. The 4Ca2+.troponin C dimers dissociate upon binding melittin, mastoparan, and peptides based on residues 96-115, 1-30, and 1-40 in the troponin I sequence. This result suggests that the peptide-binding sites overlap with the regions of contact between troponin C molecules forming a dimer. Like the structurally homologous calcium-binding protein calmodulin, troponin C shows conformational flexibility upon binding different peptides. Upon binding melittin, troponin C contracts in a similar manner to calmodulin when it binds peptides known to form amphiphilic helices (e.g., melittin, mastoparan, or MLCK-I). In contrast, mastoparan binding to troponin C does not result in a contracted structure. The scattering data indicate troponin C also remains in an extended structure upon binding the inhibitory peptides having the same sequence as residues 96-115 in troponin I.