New papers on nitrile hydratase enzymes

A couple of NHase papers, one new and the other upcoming:

• Biosynthesis of 2-amino-2,3-dimethylbutyramide by nitrile hydratase from a newly isolated cyanide-resistant strain of Rhodococcus qingshengii  by  Zhi-Jian Lin, Ren-Chao Zheng, Yu-Guo Zheng and Yin-Chu Shen in Biotechnology Letters, DOI: 10.1007/s10529-011-0623-7.

This paper reports a Rhodoccocus which can do the usual nitrile hydration reaction but can do it in the presence of significant quantities of cyanide. The paper describes whole-cell biotransformation conditions but I am guessing from the species this is an iron-centred NHase. We have found that iron-centred NHases tend to be a bit more tolerant of cyanide than the cobalt-centred ones which sounds hopeful if you want to have a play with getting some dynamic kinetic resolution of mandelonitrile type structures but they also tend to be a lot less chirally selective too! There is no chiral analysis in this paper, and obviously you don’t know if the cyanide resistance is due to cell structure or enzyme specific with this whole cell biotransformation.

• Biotransformation of nitriles to hydroxamic acids via a nitrile hydratase-amidase cascade reaction by Vojtěch Vejvoda, Ludmila Martínková, Alicja B. Veselá, Ondřej Kaplan, Sabine Lutz-Wahl, Lutz Fischer and Bronislava Uhnáková in  Journal of Molecular Catalysis B: Enzymatic,  article in press at doi:10.1016/j.molcatb.2011.03.008

This paper describes the use of a two enzyme system to hydrate a number of alkyl and aryl nitriles to the related hydroxamic acid via a NHase-produced amide. Hydroxamic acids are an interesting endpoint because they form a coloured complex with ferric ions so there is leeway here to make a screen for enzyme activity. Interestingly, Martínková’s team develop a system using either the NHase from Rhodoccocus erythropolis A4 (as a cell free extract) or cell free extracts from E. coli clones bearing the NHases from either a strain of Raoultella terrigena or Klebsiella oxytoca. Obviously the Rhodoccocus is iron centred, but the other two are cobalt-centred, and the latter pair appear to be more robust towards hydroxylamine which is a nice contrast to the usual cyanide sensitivity. When I first started looking at nitrile-active enzymes a few years back, I came across a paper by Dadd (Biotechnology Letters 23; 221-225, 2001) showing how a whole cell preparation of Rhodoccocus rhodocrous LL100-21 could be used to this transformation though the authors ascribe the reaction to the nitrilase onboard this strain- interesting to see that this transformation works with both flavours of NHase too.