Cyanide dihydratase

Jandyala D, M Berman, PD Myers, BT Sewell, RC Willson, MJ Benedik (2003) CynD, the cyanide dihydratase from Bacillus pumilus gene cloning and structural studies. Appl Environ Microbiol 69 4794-4805. 

Meyers PR, Rawlings DE, Woods DR, et al. 1993. Isolation and characterization of a cyanide dihydratase from Bacillus pumilus Cl. J Bacteriol 175(19) 6105-6112. 

Cyanide hydratase and cyanide dihydratase belongs to the nitrilase branch of nitrilase superfamily, using HCN as the only efficient substrate and producing amide and acid products, respectively. Microorganisms appear in fact to have evolved separate metabolic pathways for the hydrolysis of inorganic cyanide. Thus, most nitrilases (as well as nitrile hydratases) till now investigated do not display activity... 

Bacillus pumilus strains Cl and Cyanide dihydratase Jandhyala et al. (2003)... 

Jandhyala, D.M., Berman, M., Meyers, P.R., et al. 2003. Cyn D, the cyanide dihydratase from Bacillus pumillus Gene cloning and structural studies. Appied and Environmental Microbiology, 69 4794-4805. 

On the basis of sequence data and biochemical characterization, this chapter wiU compare the structure and enzymatic properties of nitrilases from filamentous fungi with those of prokaryotic and plant nitrilases as well as other related enzymes like cyanide hydratases and cyanide dihydratases. The biotechnological potential of fungal nitrilases will be evaluated. 

Cyanide dihydratases are also HCN specific, but differ in the reaction mechanism, which leads to formate. Their phylogenetic distribution is also different these enzymes occur in bacteria, for instance. Bacillus pumilus [21] or Pseudomonas... 

Table 14.1 Subunit and holoenzyme molecular masses of nitrilases from filamentous fungi comparison with selected prokaryotic nitrilases, cyanide hydratases and cyanide dihydratase.

Nitrilases are classified into branch 1 of the nitrilase superfamily, which is comprised of enzymes acting on various nonpeptide CN bonds [15]. All the proteins of this superfamily are characterized by a conserved catalytic triade (glu, lys, cys) and an additional conserved glu residue that seems to participate in the reaction mechanism [2]. Members of class 1 transform the CN bonds in nitriles and cyanides. The enzymes in which these activities were confirmed share in some cases levels of aa sequence identity as low as about 20%. This sequence diversity is reflected in different substrate specificities and different reaction products (carboxylic acids, amides) in various subtypes of these enzymes (aromatic nitrilases, aliphatic nitrilases, arylacetonitrilases, cyanide hydratases, cyanide dihydratases). 

Cyanide dihydratases also act on cyanide but convert it into formiate and ammonia, and can be therefore classified as hydrolases. 

The nitrilase from F. solani IMI196840 also differs from other fungal nitrilases in terms of its value for benzonitrile (0.039 mM) [10], which is markedly lower than those of other fungal nitrilases (0.2-1.5mM) [11, 14, 15]. In general, even higher fCm-values, that is in the range of 2.6-12 mM for wild-type enzymes and 5.9-90 mM for hexahistidine-tagged enzymes, have been determined for cyanide hydratases/dihydratases [17]. 

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