Structural basis for thermophilic protein stability : structures of thermophilic and mesophilic malate dehydrogenases.

• 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. (c) 2002 Elsevier Science Ltd.

Subject headings

NATURVETENSKAP  -- Biologi -- Strukturbiologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Structural Biology (hsv//eng)

Keyword

Amino Acid Sequence

Archaea/enzymology/genetics

Bacteria/enzymology/genetics

Catalytic Domain

Chlorobi/enzymology/genetics

Crystallography; X-Ray

Dimerization

Electrostatics

Enzyme Stability

L-Lactate Dehydrogenase/chemistry/genetics

Malate Dehydrogenase/*chemistry

Models; Molecular

Molecular Sequence Data

Protein Conformation

Protein Structure; Quaternary

Protein Subunits

Recombinant Proteins/chemistry/genetics

Sequence Homology; Amino Acid

Temperature

Structural biology

Strukturbiologi

Publication and Content Type

ref (subject category)

art (subject category)