{PDOC50007}
{PS50007; PIPLC_X_DOMAIN}
{PS50008; PIPLC_Y_DOMAIN}
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* Phosphatidylinositol-specific phospholipase C profiles *
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Phosphatidylinositol-specific phospholipase  C  (EC  3.1.4.11),  an eukaryotic
intracellular enzyme, plays an important role in signal transduction processes
[1]. It   catalyzes   the   hydrolysis  of  1-phosphatidyl-D-myo-inositol-4,5-
diphosphate into  the  second messenger molecules diacylglycerol and inositol-
1,4,5-triphosphate. This catalytic process is tightly regulated  by reversible
phosphorylation and binding of regulatory proteins [2 to 4].

In mammals, there  are at least 6 different isoforms of PI-PLC, they differ in
their domain structure, their regulation, and their tissue distribution. Lower
eukaryotes also possess multiple isoforms of PI-PLC.

All eukaryotic PI-PLCs  contain two regions of homology, sometimes referred to
as 'X-box'  and  'Y-box'.  The  order  of these two regions is always the same
(NH2-X-Y-COOH), but  the  spacing  is variable. In most isoforms, the distance
between these  two  regions  is only 50-100 residues but in the gamma isoforms
one PH domain,  two  SH2 domains,  and one SH3 domain are inserted between the
two PLC-specific  domains.  The  two  conserved  regions have been shown to be
important for the catalytic activity. At the C-terminal of the Y-box, there is
a C2 domain  (see  <PDOC00380>)  possibly  involved  in  Ca-dependent membrane
attachment.

By profile analysis, we  could show that sequences with significant similarity
to the  X-box  domain  occur  also  in prokaryotic and trypanosome PI-specific
phospholipases C.  Apart  from  this  region,  the prokaryotic enzymes show no
similarity to their eukaryotic counterparts.

We developed two profiles, one covering the X-box, the other the Y-box.

-Sequences known to belong to this class detected by the X-box profile: ALL.
 known eukaryotic and prokaryotic PI-PLCs.
-Other sequence(s) detected in Swiss-Prot: 1.

-Sequences known to belong to this class detected by the Y-box profile: ALL.
 known eukaryotic PI-PLCs.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Last update: July 2003 / Text revised.

[ 1] Meldrum E., Parker P.J., Carozzi A.
     "The PtdIns-PLC superfamily and signal transduction."
     Biochim. Biophys. Acta 1092:49-71(1991).
     PubMed=1849017
[ 2] Rhee S.G., Choi K.D.
     "Multiple forms of phospholipase C isozymes and their activation
     mechanisms."
     Adv. Second Messenger Phosphoprotein Res. 26:35-61(1992).
     PubMed=1419362
[ 3] Rhee S.G., Choi K.D.
     "Regulation of inositol phospholipid-specific phospholipase C
     isozymes."
     J. Biol. Chem. 267:12393-12396(1992).
     PubMed=1319994
[ 4] Sternweis P.C., Smrcka A.V.
     "Regulation of phospholipase C by G proteins."
     Trends Biochem. Sci. 17:502-506(1992).
     PubMed=1335185

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