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.

卤素脱卤酶催化从有机卤代酸中去除卤素，对于生物修复以及其在工业化学品合成中潜在的应用具有重要意义。本研究展示了假单胞菌属Pseudomonas putida菌株PP3中的同源二聚体DehI的晶体结构，这是I组α-卤代酸脱卤酶的首个结构，能够处理l-和d-两种底物。结构分析表明，DehI单体由两个约含130个氨基酸的域组成，这两个域的序列同源性约为16%，但形成了几乎相同且独特的折叠，从而构成一个假二聚体。对活性位点的分析揭示了l-和d-两种底物相对于关键催化残基的潜在结合模式。预测 Asp189 可以激活水分子对底物手性中心的亲核攻击，导致l-或d-底物的构型发生翻转，与仅处理d-底物的酶形成鲜明对比。这些细节将为脱卤酶的未来生物工程改造提供重要参考。