一种兼具腈水合酶活性与硫氰酸水解酶活性的新型腈类降解酶

A novel nitrile degrading enzyme with both nitrile hydratase activity and thiocyanate hydrolase activity

硫氰酸水解酶(SCNase)是一种主要来自于硫杆菌属的含钴酶,能够催化焦化废水中的主要成分硫氰酸盐降解。它由3个亚基组成,其活性中心存在2个翻译后修饰氧化的半胱氨酸,并且和钴离子形成独特的爪型配位结构。硫氰酸水解酶在序列和机构上都与钴型腈水合酶有很高的相似性,但活性并不互通。通过在公共序列库里搜寻,发现了一种来自玫瑰单胞菌Roseomonas stagni的新基因型的硫氰酸水解酶。该研究表达、纯化并且对这个硫氰酸水解酶(Rose.s SCNase)进行了表征。有趣的是,Rose.s SCNase不但对硫氰酸钾有催化活性,对腈类底物也具有催化活性,这是迄今为止发现的第一个活性互通的天然腈类降解酶。Rose.s SCNase在最适pH和温度下对烟腈的比酶活为(17.8±1.3)U/mg,对丙烯腈的比酶活为(30.6±1.9)U/mg,对硫氰酸钾的比酶活为(13.5±0.9)U/mg。结构比对结果显示,位于Rose.s SCNase底物结合口袋顶部氨基酸的不同可能是其存在活性互通的原因。Rose.s SCNase可能对研究含氰基底物降解方面有巨大的帮助。

Thiocyanate hydrolase(SCNase)is a cobalt-containing enzyme mainly derived from Thiobacillus.They can catalyze the degradation of thiocyanate,a main component in coking wastewater.Thiocyanate hydrolase consists of three subunits.There are two post-translational oxidized cysteines in the active center,which form a unique claw-type coordination structure with cobalt ions.Although SCNase shares high homology with the Co-NHase,both in amino acid sequences and structure,they exclusively catalyze only their own substrates.We discovered a new genotype of thiocyanate hydrolase by searching in the public sequence database.In this study,we expressed,purified,and characterized this thiocyanate hydrolase(Rose.s SCNase).Interestingly,Rose.s SCNase had catalytic activity not only against potassium thiocyanate,but also against nitrile substrates.It is the first natural nitrile degrading enzyme discovered so far.The results of structural comparison showed that the different amino acids at the top of the substrate binding pocket of Rose.s SCNase might be the reason of the interactivity.Rose.s SCNase will be a great help to our research on the degradation of cyano-containing substrates.