THE MULTISUBUNIT ACTIVE-SITE OF FUMARASE-C FROM ESCHERICHIA-COLI

The crystal structure of the tetrameric enzyme, fumarase C from Escher ichia coli, has been determined to a resolution of 2.0 Angstrom. A tun gstate derivative used in the X-ray analysis is a competitive inhibito r and places the active site of fumarase in a region which includes at oms from three of the four subunits. The polypeptide conformation is s imilar to that of delta-crystallin and is comprised of three domains. The central domain, D2, is a unique five-helix bundle. The association of the D2 domains results in a tetramer which has a core of 20 alpha- helices. The other two domains, D1 and D3, cap the helical bundle on o pposite ends giving both the single subunit and the tetramer a dumbbel l-like appearance. Fumarase C has sequence homology to the eukaryotic fumarases, aspartase, arginosuccinate lyase, adenylosuccinate lyase an d delta-crystallin.