beta-Cyanoalanine synthase is a mitochondrial cysteine synthase-like protein in spinach and Arabidopsis.
beta-Cyano-alanine synthase (CAS; EC 4.4.1.9) plays an important role in cyanide metabolism in plants. Although the enzymatic activity of beta-cyano-Ala synthase has been detected in a variety of plants, no cDNA or gene has been identified so far. We hypothesized that the mitochondrial cysteine synthase (CS; EC 4.2.99. 8) isoform, Bsas3, could actually be identical to CAS in spinach (Spinacia oleracea) and Arabidopsis. An Arabidopsis expressed sequence tag database was searched for putative Bsas3 homologs and four new CS-like isoforms, ARAth;Bsas1;1, ARAth;Bsas3;1, ARAth;Bsas4;1, and ARAth;Bsas4;2, were identified in the process. ARAth;Bsas3;1 protein was homologous to the mitochondrial SPIol;Bsas3;1 isoform from spinach, whereas ARAth;Bsas4;1 and ARAth;Bsas4;2 proteins defined a new class within the CS-like proteins family. In contrast to spinach SPIol;Bsas1;1 and SPIol;Bsas2;1 recombinant proteins, spinach SPIol;Bsas3;1 and Arabidopsis ARAth;Bsas3;1 recombinant proteins exhibited preferred substrate specificities for the CAS reaction rather than for the CS reaction, which identified these Bsas3 isoforms as CAS. Immunoblot studies supported this conclusion. This is the first report of the identification of CAS synthase-encoding cDNAs in a living organism. A new nomenclature for CS-like proteins in plants is also proposed.
Hatzfeld
Y
Y
Chiba University, Faculty of Pharmaceutical Sciences, Laboratory of Molecular Biology and Biotechnology, Yayoi-cho 1-33, Inage-ku, Chiba 263-8522, Japan.
Maruyama
A
A
Schmidt
A
A
Noji
M
M
Ishizawa
K
K
Saito
K
K
D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D003547:Cysteine Synthase / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D019143:Evolution, Molecular; D015151:Immunoblotting; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008190:Lyases / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology* / Q000235:genetics; D010802:Phylogeny; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D018724:Spinacia oleracea / Q000201:enzymology* / Q000235:genetics; D013379:Substrate Specificity
D007527:Isoenzymes; D011994:Recombinant Proteins; D003547:Cysteine Synthase; D008190:Lyases; C019955:beta-cyanoalanine synthase