PRODUCTION, CRYSTALLIZATION, AND PRELIMINARY-X-RAY ANALYSIS OF RABBITSKELETAL-MUSCLE TROPONIN COMPLEX CONSISTING OF TROPONIN-C AND FRAGMENT(1-47) OF TROPONIN-I

Troponin is a ternary protein complex consisting of subunits TnC, TnI, and TnT, and plays a key role in calcium regulation of the skeletal a nd cardiac muscle contraction. In the present study, a partial complex (CI47) was prepared from Escherichia coli-expressed rabbit skeletal m uscle TnC and fragment 1-47 of TnI, which is obtained by chemical clea vage of an E. coli-expressed mutant of rabbit skeletal muscle TnI. Wit hin the ternary troponin complex, CI47 is thought to form a core that is resistant to proteolytic digestion, and the interaction within CI47 likely maintains the integrity of the troponin complex. Complex CI47 was crystallized in the presence of sodium citrate. The addition of tr ehalose improved the diffraction pattern of the crystals substantially . The crystal lattice belongs to the space group P3(1(2))21, with unit cell dimensions a = b = 48.2 Angstrom, c = 162 Angstrom. The asymmetr ic unit presumably contains one CI47 complex. Soaking with p-chloromer curibenzenesulfonate (PCMBS) resulted in loss of isomorphism, but enha nced the quality of the crystals. The crystals diffracted up to 2.3 An gstrom resolution, with completeness of 91% and R(merge) = 6.4%. The c rystals of PCMBS-derivative should be suitable able for X-ray studies using the multiple-wavelength anomalous diffraction technique. This is the first step for elucidating the structure of the full troponin com plex.