{PDOC00700}
{PS00901; CYS_SYNTHASE}
{BEGIN}
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* Cysteine synthase/cystathionine beta-synthase P-phosphate attachment site *
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Cysteine synthase  (EC  2.5.1.47) (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 beta-synthase (EC 4.2.1.22) [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.

-Consensus pattern: K-x-E-x(3,4)-[PAF]-[STAGC]-x-S-[IVAPM]-K-x-R-x-[STAG]-
                    x(2)-[LIVM]
                    [The second K is the pyridoxal-P attachment site]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.
-Last update: April 2006 / Pattern revised.

[ 1] Saito K., Kurosawa M., Murakoshi I.
     "Determination of a functional lysine residue of a plant cysteine
     synthase by site-directed mutagenesis, and the molecular evolutionary
     implications."
     FEBS Lett. 328:111-114(1993).
     PubMed=8344414
[ 2] Swaroop M., Bradley K., Ohura T., Tahara T., Roper M.D.,
     Rosenberg L.E., Kraus J.P.
     "Rat cystathionine beta-synthase. Gene organization and alternative
     splicing."
     J. Biol. Chem. 267:11455-11461(1992).
     PubMed=1597473

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