Crystal structure of a ternary complex of D-2-hydroxyisocaproate dehydrogenase from Lactobacillus casei, NAD+ and 2-oxoisocaproate at 1.9 A resolution.
D-2-hydroxyisocaproate dehydrogenase (D-HicDH) from Lactobacillus casei is a homodimer with 333 amino acids and a molecular mass of 37 kDa per subunit. The enzyme belongs to the protein family of NAD+-dependent D-2-hydroxycarboxylate dehydrogenases and within this family to the subgroup of D-lactate dehydrogenases (D-LDHs) ...
D-2-hydroxyisocaproate dehydrogenase (D-HicDH) from Lactobacillus casei is a homodimer with 333 amino acids and a molecular mass of 37 kDa per subunit. The enzyme belongs to the protein family of NAD+-dependent D-2-hydroxycarboxylate dehydrogenases and within this family to the subgroup of D-lactate dehydrogenases (D-LDHs). Compared with other D-LDHs D-HicDH is characterized by a very low specificity regarding size and chemical constitution of the accepted D-2-hydroxycarboxylates. Hexagonal crystals of recombinant D-HicDH in the presence of NAD+ and 2-oxoisocaproate (4-methyl-2-oxopentanoate) were grown with ammonium sulphate as precipitating agent. The structure of these crystals was solved by molecular replacement and refined to a final R-factor of 19.6% for all measured X-ray reflections in the resolution range (infinity to 1.86 A). Both NAD+ and 2-oxoisocaproate were identified in the electron density map; binding of the latter in the active site, however, competes with a sulphate ion, which is also defined by electron density. Additionally the final model contains 182 water molecules and a second sulphate ion. The binding of both an in vitro substrate and the natural cosubstrate in the active site provides substantial insight into the catalytic mechanism and allows us to assess previously published active site models for this enzyme family, in particular the two most controversial points, the role of the conserved Arg234 and substrate binding. Furthermore the overall topology and details of the D-HicDH structure are described, discussed against the background of homologous structures and compared with one closely and one distantly related protein.
Related Citations:
Crystallization and Preliminary Characterization of Crystals of D-2-Hydroxyisocaproate Dehydrogenase from Lactobacillus Casei Niefind, K., Hecht, H.J., Schomburg, D. (1994) J Mol Biol 240: 400
Roentgenkristallographische Untersuchungen an Drei Mikrobiellen Enzymen: D-2-Hydroxyisocaproat-Dehydrogenase Aus Lactobacillus Casei L-2-Hydroxyisocaproat-Dehydrogenase Aus Lactobacillus Confusus Alkalische Protease Aus Bacillus Alcalophilus/Variante Q59R Niefind, K. (1993) Thesis --: --
Potential of R-2-Hydroxyisocaproate Dehydrogenase from Lactobacillus Casei for Stereospecific Reductions Kallwass, H.K.W. (1992) Enzyme Microb Technol 14: 28
Cloning, Sequencing and Expression in Escherichia Coli of the D-2-Hydroxyisocaproate Dehydrogenase Gene of Lactobacillus Casei Lerch, H.P., Blocker, H., Kallwass, H., Hoppe, J., Tsai, H., Collins, J. (1989) Gene 78: 47
Crystallization and Molecular Properties of D-2-Hydroxyisocaproate Dehydrogenase from Lactobacillus Casei Kallwass, H., Tsai, H., Schuette, H. (1987) FEMS Microbiol Lett 43: 263
D-2-Hydroxyisocaproate Dehydrogenase from Lactobacillus Casei. A New Enzyme Suitable for Stereospecific Reduction of 2-Ketocarboxylic Acids Hummel, W., Schuette, H., Kula, M.R. (1985) Appl Microbiol Biotechnol 21: 7
Organizational Affiliation:
Gesellschaft fur Biotechnologische Forschung (GBF), Abteilung Molekulare Strukturforschung, Braunschweig, Germany.
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