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.
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.
Blechner
S L
SL
Life Sciences Division, Los Alamos National Laboratory, New Mexico 87544.
Olah
G A
GA
Strynadka
N C
NC
Hodges
R S
RS
Trewhella
J
J
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000737:chemistry*; D002413:Cations, Divalent; D006863:Hydrogen-Ion Concentration; D036341:Intercellular Signaling Peptides and Proteins; D008555:Melitten / Q000378:metabolism*; D008969:Molecular Sequence Data; D009132:Muscles / Q000737:chemistry; D010455:Peptides; D011817:Rabbits; D012542:Scattering, Radiation; D014336:Troponin / Q000737:chemistry* / Q000378:metabolism; D019209:Troponin C; D014862:Wasp Venoms / Q000378:metabolism*; D014965:X-Rays
D002413:Cations, Divalent; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D014336:Troponin; D019209:Troponin C; D014862:Wasp Venoms; D008555:Melitten; C037500:mastoparan; D002118:Calcium