The crystal structure of DehI reveals a new alpha-haloacid dehalogenase fold and active-site mechanism. (3BJX)

Haloacid dehalogenases catalyse the removal of halides from organic haloacids and are of interest for bioremediation and for their potential use in the synthesis of industrial chemicals. We present the crystal structure of the homodimer DehI from Pseudomonas putida strain PP3, the first structure of a group I alpha-haloacid dehalogenase that can process both l- and d-substrates. The structure shows that the DehI monomer consists of two domains of approximately 130 amino acids that have approximately 16% sequence identity yet adopt virtually identical and unique folds that form a pseudo-dimer. Analysis of the active site reveals the likely binding mode of both l- and d-substrates with respect to key catalytic residues. Asp189 is predicted to activate a water molecule for nucleophilic attack of the substrate chiral centre resulting in an inversion of configuration of either l- or d-substrates in contrast to d-only enzymes. These details will assist with future bioengineering of dehalogenases.

卤酸脱卤酶（haloacid dehalogenases）能够催化有机卤代酸脱去卤原子，在生物修复以及工业化学品合成中具有应用潜力，因此受到广泛关注。本研究解析了恶臭假单胞菌PP3菌株（Pseudomonas putida strain PP3）来源的同源二聚体DehI的晶体结构，这是首个可同时处理L-型和D-型底物的I型α-卤酸脱卤酶（alpha-haloacid dehalogenase）结构。结构分析显示，DehI单体由两个约含130个氨基酸的结构域组成，二者序列同源性仅约16%，却折叠为几乎完全一致且独特的构象，形成假二聚体。对活性位点的分析揭示了L-型和D-型底物相对于关键催化残基的潜在结合模式。与仅能作用于D-型底物的酶不同，研究预测Asp189会活化水分子，对底物手性中心进行亲核攻击，从而使L-或D-型底物的构型发生反转。这些细节将为脱卤酶的后续生物工程改造提供重要助力。