title: Molecular adaptation: the malate dehydrogenase from the extreme halophilic bacterium Salinibacter ruber behaves like a non-halophilic protein.
abstract: Malate dehydrogenase from the extreme halophilic bacterium, Salinibacter ruber (Sr MalDH) was purified and characterised as a tetramer by sedimentation velocity measurements, showing the enzyme belongs to the LDH-like group of MalDHs. In contrast to most other halophilic enzymes, which unfold when incubated at low salt concentration, Sr MalDH is completely stable in absence of salt. Its amino acid composition does not display the strong acidic character specific of halophilic proteins. The enzyme displays a strong KCl-concentration dependent variation in K(m) for oxaloacetate, but not for the NADH co-factor. Its activity is reduced by high salt concentration, but remains sufficient for the enzyme to sustain catalysis at approximately 30% of its maximal rates in 3 M KCl. The properties of the protein were compared with those from other LDH-like MalDHs of bacterial and archaeal origins, showing that Sr MalDH in fact behaves like a non-halophilic enzyme.
authors.affiliation: Laboratoire de Biophysique Moléculaire, Institut de Biologie Structurale CEA-CNRS-UJF, UMR 5075, 41, rue Jules-Horowitz, Grenoble 38042, France. Dominique.madern@ibs.fr
authors.forename: Dominique
authors.initials: D
authors.lastname: Madern
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Zaccai
mesh_terms: D002384:Catalysis; D004795:Enzyme Stability; D019617:Halobacterium salinarum / Q000201:enzymology* / Q000254:growth & development; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008291:Malate Dehydrogenase / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D062907:Oxaloacetic Acid / Q000378:metabolism; D011189:Potassium Chloride / Q000378:metabolism; D012492:Salts; D014461:Ultracentrifugation
chemical_list: D012492:Salts; D009243:NAD; D062907:Oxaloacetic Acid; D011189:Potassium Chloride; D007770:L-Lactate Dehydrogenase; D008291:Malate Dehydrogenase