Structural and functional studies on Troponin I and Troponin C interactions.
Troponin I (TnI) peptides (TnI inhibitory peptide residues 104-115, Ip; TnI regulatory peptide resides 1-30, TnI1-30), recombinant Troponin C (TnC) and Troponin I mutants were used to study the structural and functional relationship between TnI and TnC. Our results reveal that an intact central D/E helix in TnC is required to maintain the ability of TnC to release the TnI inhibition of the acto-S1-TM ATPase activity. Ca(2+)-titration of the TnC-TnI1-30 complex was monitored by circular dichroism. The results show that binding of TnI1-30 to TnC caused a three-folded increase in Ca(2+) affinity in the high affinity sites (III and IV) of TnC. Gel electrophoresis and high performance liquid chromatography (HPLC) studies demonstrate that the sequences of the N- and C-terminal regions of TnI interact in an anti-parallel fashion with the corresponding N- and C-domain of TnC. Our results also indicate that the N- and C-terminal domains of TnI which flank the TnI inhibitory region (residues 104 to 115) play a vital role in modulating the Ca(2+)- sensitive release of the TnI inhibitory region by TnC within the muscle filament. A modified schematic diagram of the TnC/TnI interaction is proposed.
Ngai
S M
SM
Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada. smngai@cuhk.edu.hk
Pearlstone
J R
JR
Farah
C S
CS
Reinach
F C
FC
Smillie
L B
LB
Hodges
R S
RS
D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D008969:Molecular Sequence Data; D009119:Muscle Contraction; D009126:Muscle Relaxation; D018482:Muscle, Skeletal; D009154:Mutation; D009206:Myocardium; D015879:Myosin Subfragments / Q000378:metabolism; D009218:Myosins / Q000037:antagonists & inhibitors / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011817:Rabbits; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013816:Thermodynamics; D014335:Tropomyosin / Q000378:metabolism; D019209:Troponin C / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019210:Troponin I / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D000199:Actins; D015879:Myosin Subfragments; D010446:Peptide Fragments; D011994:Recombinant Proteins; D014335:Tropomyosin; D019209:Troponin C; D019210:Troponin I; D009218:Myosins; D002118:Calcium