title: Crystal structure of L-2-hydroxyisocaproate dehydrogenase from Lactobacillus confusus at 2.2 A resolution. An example of strong asymmetry between subunits.
abstract: L-2-Hydroxyisocaproate dehydrogenase (L-HicDH) from Lactobacillus confusus, a homotetramer with a molecular mass of 33 kDa per subunit, belongs to the protein family of the NAD(+)-dependent L-2-hydroxycarboxylate dehydrogenases. L-HicDH was crystallized with ammonium sulphate as precipitant in the presence of NAD+. The crystals belong to the trigonal space group P3(2)21, with a = 135.9 A and c = 205.9 A, and diffract X-rays to 2.2 A resolution. The crystal structure was solved by Patterson search and molecular replacement techniques and refined to an R-value of 21.4% (2.2 to 8 A). The final structure model contains one NAD+ molecule and one sulphate ion per subunit, with 309 water molecules. An unusual feature of this crystal structure is the deviation of the protein subunits from non-crystallographic symmetry, which is so strong that it can be detected globally by self-rotation calculations in reciprocal space. This asymmetry is especially pronounced in the environment of the active site; it is reflected also in the nicotinamide conformation of NAD+ and allows some conclusions to be drawn about the catalytic mechanism. In this context, an "inner active site loop" is identified as a structural element of fundamental functional importance. Furthermore, with knowledge of the crystal structure of L-HicDH the differences in substrate specificity between L-HicDH and the L-lactate dehydrogenases can be partly explained.
authors.affiliation: Gesellschaft für Biotechnologische Forschung (GBF), Abteilung Molekulare Strukturforschung, Braunschweig, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Niefind
authors.forename: H J
authors.initials: HJ
authors.lastname: Hecht
authors.forename: D
authors.initials: D
authors.lastname: Schomburg
mesh_terms: D000429:Alcohol Oxidoreductases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D001665:Binding Sites; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D007770:L-Lactate Dehydrogenase / Q000737:chemistry / Q000235:genetics; D007778:Lactobacillus / Q000201:enzymology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009243:NAD / Q000378:metabolism; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D016415:Sequence Alignment; D012997:Solvents / Q000737:chemistry; D013379:Substrate Specificity; D014867:Water / Q000737:chemistry
chemical_list: D011994:Recombinant Proteins; D012997:Solvents; D014867:Water; D009243:NAD; D000429:Alcohol Oxidoreductases; C047961:2-hydroxyisocaproate dehydrogenase; D007770:L-Lactate Dehydrogenase