The cyanide hydratase from Neurospora crassa forms a helix which has a dimeric repeat
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The fungal cyanide hydratases form a functionally specialized subset of the nitrilases which catalyze the hydrolysis of cyanide to formamide with high specificity. These hold great promise for the bioremediation of cyanide wastes. The low resolution (3.0 nm) three-dimensional reconstruction of negatively stained recombinant cyanide hydratase fibers from the saprophytic fungus Neurospora crassa by iterative helical real space reconstruction reveals that enzyme fibers display left-handed D1 S5.4 symmetry with a helical rise of 1.36 nm. This arrangement differs from previously characterized microbial nitrilases which demonstrate a structure built along similar principles but with a reduced helical twist. The cyanide hydratase assembly is stabilized by two dyadic interactions between dimers across the one-start helical groove. Docking of a homology-derived atomic model into the experimentally determined negative stain envelope suggests the location of charged residues which may form salt bridges and stabilize the helix.
KeywordsCyanide Nitrilase 3d protein reconstruction Cyanide hydratase
We thank Professor Edward H. Egelman for his assistance with the IHRSR programs and interpretation of the helical power spectrum, Mohammed Jaffer for assistance with the electron microscope, Dr. Arvind Varsani for his assistance with expression, and the Carnegie Corporation of New York, the National Research Foundation, the University of Cape Town, the Texas Hazardous Waste Research Center, and the Robert A. Welch Foundation (A-1310) for financial support.
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