The gene for a halophilic glutamate dehydrogenase sequence, transcription analysis and phylogenetic implications

Abstract

We have isolated and sequenced the gene for a putative NADP-dependent glutamate dehydrogenase from the extremely halophilic archaebacterium Halobacterium salinarium. This gene is transcribed as a unique RNA molecule of about 1700 nucleotides. The 5' end of the transcript contains characteristic consensus transcription initiation and promoter sequences observed in halophilic archaebacteria. The encoded polypeptide, with a predicted length of 435 amino acids, shows significant overall homology and conservation of functional domains when compared with different eubacterial and eukaryotic glutamate dehydrogenases. Surprisingly, the archaebacterial protein shares a larger number of identical amino acid residues with homologous polypeptides from higher eukaryotes than with those from unicellular eukaryotes and eubacteria.

Insights into the Molecular Basis of Salt Tolerance from the Study of Glutamate Dehydrogenase from Halobacterium salinarum

“…In the Hs model these appear to occupy positions where, were they also to be acidic, they would otherwise result in charge repulsion effects. This feature has been noted in the halophilic ferredoxin from H. marismortui, where serine residues have been found on the enzyme surface sandwiched be- 6 M. Kalinowski and P. C. Engel, unpublished results.…”

“…For example, the GluDH from Hs is still active in 4 M KCl, whereas that from the mesophile Cs is potently inhibited at such high concentrations. 6 The second common property of these halophilic enzymes is that many of those isolated to date are rapidly and irreversibly inactivated by exposure to solutions of low ionic strength. For example, the Hs GluDH is markedly unstable below 1 M KCl unless the salt is replaced by a compatible solute such as betaine (26).…”

“…Sequence Alignment-The GluDH sequences from a diverse range of species show a very high degree of sequence similarity (6,11,12). Furthermore, the structures of this enzyme from Cs and Pf are also very similar (10), strongly suggesting that the core of the three-dimensional structures of GluDH are highly conserved, and therefore these structures can serve as models for all other hexameric GluDHs.…”

“…The amino acid sequence of glutamate dehydrogenase (GluDH) 1 from Halobacterium salinarum (Hs) reveals that this enzyme contains a high number of acidic amino acids (6,7), but as yet, a three-dimensional structure is not available for this GluDH. In previous work we have determined the high resolution structures of the GluDHs from the mesophile Clostridium symbiosum (Cs) (8,9) and from the hyperthermophilic archaeon Pyrococcus furiosus (Pf) (10).…”

Insights into Thermal Stability from a Comparison of the Glutamate Dehydrogenases from Pyrococcus furiosus and Thermococcus litoralis

“…Sequence comparisons show that the hexameric enzymes are structurally homologous, whatever their coenzyme specificity (Lilley et al, 1991;Baker et al, 1992b). To date, the sequences of six GluDHs from Archaea have been published and these show significant similarity to the eubacterial GluDHs (Benachenhou and Baldacci, 1991;Maras et al, 1992;DiRuggiero et al, 1993;Benachenhou-Lahfa et al, 1994). The best-studied of these hyperthermophilic microorganisms is P: furiosus, which grows at temperature up to 103°C (Klump et al, 1992).…”