THE STRUCTURE OF A TRIMERIC ARCHAEAL ADENYLATE KINASE

The adenylate kinase from the hyperthermophilic archaean species Sulfo lobus acidocaldarius has been cloned, expressed in Escherichia coli, p urified and crystallized. The crystal structure was elucidated by mult iple isomorphous replacement and non-crystallographic density averagin g. The structure was refined at 2.6 Angstrom (1 Angstrom = 0.1 nm) res olution. The enzyme is trimeric, in contrast to previous solution meas urements that suggested a dimeric structure, and in contrast to the va st majority of adenylate kinases, which are monomeric. Ln large parts of each subunit the chain fold resembles the known enzyme structure fr om eubacteria and eukaryotes although the sequence homology is negligi ble. Since the asymmetric unit contains two trimers with and without b ound AMP at the AMP sites and with an ADP at one of the six ATP sites, the analysis shows the enzyme in several states. The conformational d ifferences between these states resemble those of other adenylate kina ses. Because of sequence homology, the structure presented provides a good model for the methanococcal adenylate kinases. (C) 1998 Academic Press.