J. Biol. Chem., Vol. 266, Issue 21, 13746-13751, 07, 1991
Cross-linking of residue 57 in the regulatory domain of a mutant rabbit skeletal muscle troponin C to the inhibitory region of troponin I
T Kobayashi, T Tao, Z Grabarek, J Gergely and JH Collins
Department of Biological Chemistry, School of Medicine and Medical Biotechnology, University of Maryland, Baltimore 21201.
Interactions between troponin C (TnC) and troponin I (TnI) play an
important role in the Ca(2+)-dependent regulation of vertebrate striated
muscle contraction. In the present study, we investigated the sites of
interaction between the N-terminal regulatory domain of TnC and the
inhibitory region (residues 96-116) of TnI, using a mutant rabbit skeletal
TnC (designated as TnC57) that contains a single Cys at residue 57 in the
C-helix. TnC57 was modified with the photoreactive cross-linker
4-maleimidobenzophenone (BP-Mal), and, after formation of a binary complex
with TnI, cross-linking between the proteins was induced by photolysis. The
resulting product was cleaved with CNBr and several proteases, and peptides
containing cross-links were purified and subjected to amino acid
sequencing. The results show that Cys-57 of TnC57 is cross-linked to the
segment of TnI spanning residues 113-121. Previously, we showed that Cys-98
of TnC can be cross-linked via BP-Mal to TnI residues 103-110 (Leszyk, J.,
Collins, J.H., Leavis, P.C., and Tao, T. (1987) Biochemistry 26,
7042-7047). Taken together, these results demonstrate that both the C- and
the N-terminal domains of TnC interact with the inhibitory region of TnI
and are consistent with the hypothesis that, in a complex with TnI, TnC
adopts a more compact conformation than in the crystal structure.