The glutamine synthetase from the hyperthermoacidophilic crenarcheon Sulfolobus acidocaldarius: Isolation, characterization and sequencing of the gene

The glutamine synthetase (EC 6.3.1.2) from the hyper-thermoacidophilic cren archeon Sulfolobus acidocaldarius (DSM 639) was purified to homogeneity, ch aracterized and the glnA gene isolated and sequenced. The amount of enzyme present in the cytosolic fraction from Sulfolobos cells showed a strong var iation depending on the carbon and nitrogen sources in the growth medium. T he enzyme was found to be a dodecameric protein composed of identical subun its of 52 kDa. it was stable at 78 degrees C in the presence of Mn2+ ions. The catalytic activity was regulated solely by feed-back inhibition through L-alanine and glycine and not by adenylylation, No evidence for the presen ce of isoenzymes was found. Sequence comparison showed that the Sulfolobus protein is most closely related to the glutamine synthetases of the I-P typ e despite its regulatory properties and the finding that the known euryarch eal glutamine synthetase sequences belong to the I-alpha subgroup of these enzymes. Our phylogenetic analysis suggests that the gene duplication leadi ng to the development of the I-alpha and I-beta enzymes preceded the separa tion of the archea and the bacteria.