Spectroscopic and ITC study of the conformational change upon Ca2+-binding in TnC C-lobe and TnI peptide complex from Akazara scallop striated muscle.
Akazara scallop (Chlamys nipponensis akazara) troponin C (TnC) of striated adductor muscle binds only one Ca(2+) ion at the C-terminal EF-hand motif (Site IV), but it works as the Ca(2+)-dependent regulator in adductor muscle contraction. In addition, the scallop troponin (Tn) has been thought to regulate muscle contraction via activating mechanisms that involve the region spanning from the TnC C-lobe (C-lobe) binding site to the inhibitory region of the TnI, and no alternative binding of the TnI C-terminal region to TnC because of no similarity between second TnC-binding regions of vertebrate and the scallop TnIs. To clarify the Ca(2+)-regulatory mechanism of muscle contraction by scallop Tn, we have analyzed the Ca(2+)-binding properties of the complex of TnC C-lobe and TnI peptide, and their interaction using isothermal titration microcalorimetry, nuclear magnetic resonance, circular dichroism, and gel filtration chromatography. The results showed that single Ca(2+)-binding to the Site IV leads to a structural transition not only in Site IV but also Site III through the structural network in the C-lobe of scallop TnC. We therefore assumed that the effect of Ca(2+)-binding must lead to a change in the interaction mode between the C-lobe of TnC and the TnI peptide. The change should be the first event of the transmission of Ca(2+) signal to TnI in Tn ternary complex.
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
Fumiaki
F
Yumoto
Hiroyuki
H
Tanaka
Koji
K
Nagata
Yumiko
Y
Miyauchi
Takuya
T
Miyakawa
Takao
T
Ojima
Masaru
M
Tanokura
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism*; D002478:Cells, Cultured; D009682:Magnetic Resonance Spectroscopy; D018482:Muscle, Skeletal / Q000502:physiology* / Q000648:ultrastructure*; D049897:Pectinidae; D011485:Protein Binding; D011487:Protein Conformation; D019209:Troponin C / Q000378:metabolism* / Q000648:ultrastructure*; D019210:Troponin I / Q000378:metabolism* / Q000648:ultrastructure*
D019209:Troponin C; D019210:Troponin I; D002118:Calcium