REFINED CRYSTAL STRUCTURES OF UNLIGATED ADENYLOSUCCINATE SYNTHETASE FROM ESCHERICHIA COLI

摘要

Crystal structures of unligated adenylosuccinate synthetase from Escherchia coli in space groups P2(1) and P2(1)2(1)2(1) have been refined to R-factors of 0.199 and 0.206 against data to 2.0 and 2.5 Angstrom, respectively. Bond lengths and angles deviate from expected values by 0.011 Angstrom and 1.7 degrees for the P2(1) crystal form and by 0.015 Angstrom and 1.7 degrees for the P2(1)2(1)2(1) crystal form. The fold of the polypeptide chain is dominated by a central beta-sheet, which is composed of nine parallel strands and a tenth antiparallel strand. Extending off from this central beta-sheet are four subdomains. The four subdomains contribute loops of residues that are disordered or have high thermal parameters. At least three of these loops (residues 42 to 52, 120 to 131 and 298 to 304) contribute essential residues to the putative active site of the synthetase. In the absence of ligands, much of the active site of the synthetase exists in an ill-defined conformational state.