PROSITE documentation PDOC00700
Cysteine synthase/cystathionine beta-synthase P-phosphate attachment site


Cysteine synthase (EC (CSase) is the pyridoxal-phosphate dependent enzyme responsible [1] for the formation of cysteine from O-acetyl-serine and hydrogen sulfide with the concomitant release of acetic acid. In bacteria such as Escherichia coli, two forms of the enzyme are known (genes cysK and cysM). In plants there are also two forms, one located in the cytoplasm and the other in chloroplasts.

Cystathionine β-synthase (EC [2] catalyzes the first irreversible step in homocysteine transulfuration; the conjugation of homocysteine and serine forming cystathionine. Like Csase it is a pyridoxal-phosphate dependent enzyme.

The two types of enzymes are evolutionary related. The pyridoxal-phosphate group of CSases has been shown to be attached to a lysine residue which is located in the N-terminal section of these enzymes; the sequence around this residue is highly conserved and can be used as a signature pattern to detect this class of enzymes.

Last update:

April 2006 / Pattern revised.


Technical section

PROSITE method (with tools and information) covered by this documentation:

CYS_SYNTHASE, PS00901; Cysteine synthase/cystathionine beta-synthase P-phosphate attachment site  (PATTERN)


1AuthorsSaito K. Kurosawa M. Murakoshi I.
TitleDetermination of a functional lysine residue of a plant cysteine synthase by site-directed mutagenesis, and the molecular evolutionary implications.
SourceFEBS Lett. 328:111-114(1993).
PubMed ID8344414

2AuthorsSwaroop M. Bradley K. Ohura T. Tahara T. Roper M.D. Rosenberg L.E. Kraus J.P.
TitleRat cystathionine beta-synthase. Gene organization and alternative splicing.
SourceJ. Biol. Chem. 267:11455-11461(1992).
PubMed ID1597473

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