title: Structural basis for thermophilic protein stability: structures of thermophilic and mesophilic malate dehydrogenases.
abstract: The three-dimensional structure of four malate dehydrogenases (MDH) from thermophilic and mesophilic phototropic bacteria have been determined by X-ray crystallography and the corresponding structures compared. In contrast to the dimeric quaternary structure of most MDHs, these MDHs are tetramers and are structurally related to tetrameric malate dehydrogenases from Archaea and to lactate dehydrogenases. The tetramers are dimers of dimers, where the structures of each subunit and the dimers are similar to the dimeric malate dehydrogenases. The difference in optimal growth temperature of the corresponding organisms is relatively small, ranging from 32 to 55 degrees C. Nevertheless, on the basis of the four crystal structures, a number of factors that are likely to contribute to the relative thermostability in the present series have been identified. It appears from the results obtained, that the difference in thermostability between MDH from the mesophilic Chlorobium vibrioforme on one hand and from the moderate thermophile Chlorobium tepidum on the other hand is mainly due to the presence of polar residues that form additional hydrogen bonds within each subunit. Furthermore, for the even more thermostable Chloroflexus aurantiacus MDH, the use of charged residues to form additional ionic interactions across the dimer-dimer interface is favored. This enzyme has a favorable intercalation of His-Trp as well as additional aromatic contacts at the monomer-monomer interface in each dimer. A structural alignment of tetrameric and dimeric prokaryotic MDHs reveal that structural elements that differ among dimeric and tetrameric MDHs are located in a few loop regions.
authors.affiliation: Department of Chemistry, University of Oslo, Box 1033, Blindern, N-0316 Oslo, Norway.
authors.forename: Bjørn
authors.initials: B
authors.lastname: Dalhus
authors.forename: Markuu
authors.initials: M
authors.lastname: Saarinen
authors.forename: Uwe H
authors.initials: UH
authors.lastname: Sauer
authors.forename: Pär
authors.initials: P
authors.lastname: Eklund
authors.forename: Kenth
authors.initials: K
authors.lastname: Johansson
authors.forename: Andreas
authors.initials: A
authors.lastname: Karlsson
authors.forename: S
authors.initials: S
authors.lastname: Ramaswamy
authors.forename: Alexandra
authors.initials: A
authors.lastname: Bjørk
authors.forename: Bjørnar
authors.initials: B
authors.lastname: Synstad
authors.forename: Kristine
authors.initials: K
authors.lastname: Naterstad
authors.forename: Reidun
authors.initials: R
authors.lastname: Sirevåg
authors.forename: Hans
authors.initials: H
authors.lastname: Eklund
mesh_terms: D000595:Amino Acid Sequence; D001105:Archaea / Q000201:enzymology / Q000235:genetics; D001419:Bacteria / Q000201:enzymology / Q000235:genetics; D020134:Catalytic Domain; D019414:Chlorobi / Q000201:enzymology / Q000235:genetics; D018360:Crystallography, X-Ray; D019281:Dimerization; D004795:Enzyme Stability; D007770:L-Lactate Dehydrogenase / Q000737:chemistry / Q000235:genetics; D008291:Malate Dehydrogenase / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D020836:Protein Structure, Quaternary; D021122:Protein Subunits; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D013696:Temperature
chemical_list: D021122:Protein Subunits; D011994:Recombinant Proteins; D007770:L-Lactate Dehydrogenase; D008291:Malate Dehydrogenase