Characterization of the Pseudomonas pseudoalcaligenes CECT5344 Cyanase, an enzyme that is not essential for cyanide assimilation.
Cyanase catalyzes the decomposition of cyanate into CO(2) and ammonium, with carbamate as an unstable intermediate. The cyanase of Pseudomonas pseudoalcaligenes CECT5344 was negatively regulated by ammonium and positively regulated by cyanate, cyanide, and some cyanometallic complexes. Cyanase activity was not detected in cell extracts from cells grown with ammonium, even in the presence of cyanate. Nevertheless, a low level of cyanase activity was detected in nitrogen-starved cells. The cyn gene cluster of P. pseudoalcaligenes CECT5344 was cloned and analyzed. The cynA, cynB, and cynD genes encode an ABC-type transporter, the cynS gene codes for the cyanase, and the cynF gene encodes a novel sigma(54)-dependent transcriptional regulator which is not present in other bacterial cyn gene clusters. The CynS protein was expressed in Escherichia coli and purified by following a simple and rapid protocol. The P. pseudoalcaligenes cyanase showed an optimal pH of 8.5 degrees C and a temperature of 65 degrees C. An insertion mutation was generated in the cynS gene. The resulting mutant was unable to use cyanate as the sole nitrogen source but showed the same resistance to cyanate as the wild-type strain. These results, in conjunction with the induction pattern of the enzymatic activity, suggest that the enzyme has an assimilatory function. Although the induction of cyanase activity in cyanide-degrading cells suggests that some cyanate may be generated from cyanide, the cynS mutant was not affected in its ability to degrade cyanide, which unambiguously indicates that cyanate is not a central metabolite in cyanide assimilation.
Luque-Almagro
Víctor M
VM
Departamento de Bioquímica y Biología Molecular y Genética, Facultad de Veterinaria, Universidad de Extremadura, Cáceres, Spain.
Huertas
María-J
MJ
Sáez
Lara P
LP
Luque-Romero
Manuel Martínez
MM
Moreno-Vivián
Conrado
C
Castillo
Francisco
F
Roldán
M Dolores
MD
Blasco
Rafael
R
D018528:ATP-Binding Cassette Transporters / Q000235:genetics; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D019759:Carbon-Nitrogen Lyases / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D003001:Cloning, Molecular; D003485:Cyanates / Q000378:metabolism; D003486:Cyanides / Q000378:metabolism*; D004795:Enzyme Stability; D004926:Escherichia coli / Q000235:genetics; D017353:Gene Deletion; D015870:Gene Expression; D015964:Gene Expression Regulation, Bacterial; D023061:Gene Order; D005798:Genes, Bacterial; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D005810:Multigene Family; D016254:Mutagenesis, Insertional; D044205:Pseudomonas pseudoalcaligenes / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D013696:Temperature; D014157:Transcription Factors / Q000235:genetics
D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D003485:Cyanates; D003486:Cyanides; D000644:Quaternary Ammonium Compounds; D014157:Transcription Factors; C019953:cyanate hydrolase; D019759:Carbon-Nitrogen Lyases