Journal
PLANT MOLECULAR BIOLOGY REPORTER
Volume 29, Issue 3, Pages 514-524Publisher
SPRINGER
DOI: 10.1007/s11105-010-0255-4
Keywords
Cassava; Cyanogenic glycosides; beta-Cyanoalanine synthase; Cysteine synthase; Cyanide detoxification
Categories
Funding
- National Science Foundation [IOS 0641084]
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Cassava is an important staple food crop, feeding 600 million people worldwide, which produce cyanogenic glycosides. Cyanogenic glycosides in cassava are known to act as a deterrent for herbivores as well as serve as a mobile source of reduced nitrogen. Cassava is also equipped with a cyanide detoxification pathway, mediated by beta-cyanoalanine synthase (beta-CAS) which converts cyanide into asparagine. beta-CAS, belonging to the Bsas family of enzymes, is multi functional and shares sequence homology with cysteine synthase (CS). Using rapid amplification of cDNA end-polymerase chain reaction (RACE-PCR), two cDNA sequences were isolated from cassava. The two clones named MANes; BsasA (accession no. EU350583) and MANes; BsasB (accession no. HQ257219), showed high homology to known beta-CAS enzymes (80% and 75% amino acid similarity to Arabidopsis and 76% and 82% similarity to spinach, respectively). The kinetic properties of the two clones were characterized in a Escherichia coli NK3 mutant strain which lacks activity for any of the Bsas proteins. Kinetic studies showed that MANes; BsasB is a beta-CAS with a CAS/CS activity ratio of 72 while MANes; BsasA is a CS showing bifunctional capabilities and with a CAS/CS activity ratio of 11. The isolation of cassava beta-CAS and CS genes reported here paves the way for their utilization in genetically enhancing the cyanide detoxification potential of cassava and/or increase of the essential amino acid cysteine, which has been found to be low in nutritionally compromised individuals.
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