A special bifunctional enzyme from Alcaligenes sp. DN25 and its
enzymatic degradation of cyanide
Abstract
Deepening and expanding the understanding of cyanide-degrading enzymes
are the foundation of developing new technology for cyanide
bioremediation. In this study, a putative cyanide-degrading enzyme gene
from Alcaligenes sp. DN25(CGMCC 5734) was cloned and expressed in
Escherichia coli. The purified recombinant enzyme named as cdE,
consisting of a 38-kDa polypeptide, showed 99% amino acid sequence
identity with cyanidase derived from Pseudomonas stutzeri AK61. However,
the cdE was supposed to have both cyanide dihydratase (CynD) and cyanide
hydratase (CHT) activities based on the findings that formate, ammonium
and formamide were simultaneously generated during cyanide enzymatic
degradation. The enzymatic properties of cdE were characterized with an
optimal activity at a temperature of 30°C, pH of 7.0, and could even
maintain approximately 50% activity at pH 9.0. More importantly, the
selectivity of enzymatic reaction pathway was suggested related to the
conformation stability of the cdE that affected by the modifications of
amino acids near the active site as well as the degradation conditions,
leading to produce different ratios of formate and formamide. As far as
we know, this is the first report of a cyanide-degrading enzyme
possessing bifunctional catalysis activity, which might become
a supplement of cyanide-degrading enzyme databases.