ABSTRACT

Enzymes related to β-hydroxyacid dehydrogenases/3-hydroxyisobutyrate dehydrogenases are ubiquitous, but most of them have not been characterized. An uncharacterized protein with moderate sequence similarities to Gluconobacter oxydans succinic semialdehyde reductase and plant glyoxylate reductases/succinic semialdehyde reductases was found in the genome of Acetobacter aceti JCM20276. The corresponding gene was cloned and expressed in Escherichia coli. The gene product was purified and identified as a glyoxylate reductase that exclusively catalyzed the NAD(P)H-dependent reduction of glyoxylate to glycolate. The strict substrate specificity of this enzyme to glyoxylate, the diverged sequence motifs for its binding sites with cofactors and substrates, and its phylogenetic relationship to homologous enzymes suggested that this enzyme represents a novel class of enzymes in the β-hydroxyacid dehydrogenase family. This study may provide an important clue to clarify the metabolism of glyoxylate in bacteria.

Abbreviations: GR: glyoxylate reductase; GRHPR: glyoxylate reductase/hydroxypyruvate reductase; HIBADH: 3-hydroxyisobutyrate dehydrogenase; SSA: succinic semialdehyde; SSAR: succinic semialdehyde reductase

摘要

与β-羟酸脱氢酶/ 3-羟基异丁酸酯脱氢酶有关的酶是普遍存在的，但是大多数尚未被表征。在醋酸醋杆菌JCM20276的基因组中发现了一个与氧化葡糖杆菌琥珀酸半醛还原酶和植物乙醛酸还原酶/琥珀酸半醛还原酶具有中等序列相似性的未表征蛋白质。克隆了相应的基因并在大肠杆菌中表达。纯化基因产物并将其鉴定为乙醛酸还原酶，该酶专门催化NAD（P）H依赖的乙醛酸还原为乙醇酸。该酶对乙醛酸的严格底物特异性，其与辅因子和底物结合位点的不同序列基序及其与同源酶的系统发生关系表明，该酶代表了β-羟酸脱氢酶家族中一类新型的酶。这项研究可能为阐明细菌中乙醛酸的代谢提供重要线索。

缩写：GR：乙醛酸还原酶；GRHPR：乙醛酸还原酶/羟基丙酮酸还原酶；HIBADH：3-羟基异丁酸酯脱氢酶；SSA：琥珀酸半醛；SSAR：琥珀酸半醛还原酶