{PDOC00145}
{PS00161; ISOCITRATE_LYASE}
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* Isocitrate lyase signature *
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Isocitrate lyase (EC 4.1.3.1) [1,2] is an enzyme that catalyzes the conversion
of isocitrate  to  succinate and glyoxylate.   This  is the  first step in the
glyoxylate bypass, an alternative to the tricarboxylic acid cycle in bacteria,
fungi and plants.

A cysteine,  a  histidine  and  a glutamate or aspartate have been found to be
important for  the  enzyme's  catalytic activity. Only one cysteine residue is
conserved between the sequences of the fungal, plant and bacterial enzymes; it
is located  in  the  middle  of  a conserved hexapeptide that can be used as a
signature pattern for this type of enzyme.

ICL is evolutionary related to two other type of enzymes:

 - Carboxyphosphonoenolpyruvate phosphonomutase  (EC 2.7.8.23)  (CPEP mutase).
   It forms   a   carbon-phosphorus  bond  in  a  rearrangement  leading  from
   carboxyphosphonoenolpyruvate (CPEP) to phosphinopyruvate.
 - Phosphoenolpyruvate phosphomutase (EC 5.4.2.9) (PEP mutase) [3]. It forms a
   carbon-phosphorus bond   by   converting   phosphoenolpyruvate   (PEP)   to
   phosphonopyruvate.

-Consensus pattern: K-[KR]-C-G-H-[LMQR]
                    [C may be an active site residue]
-Sequences known to belong to this class detected by the pattern: All ICLs and
 CPEP mutases, but not PEP mutases.
-Other sequence(s) detected in Swiss-Prot: NONE.
-Last update: May 2004 / Text revised.

[ 1] Beeching J.R.
     "High sequence conservation between isocitrate lyase from Escherichia
     coli and Ricinus communis."
     Protein Seq. Data Anal. 2:463-466(1989).
     PubMed=2696959
[ 2] Atomi H., Ueda M., Hikida M., Hishida T., Teranishi Y., Tanaka A.
     "Peroxisomal isocitrate lyase of the n-alkane-assimilating yeast
     Candida tropicalis: gene analysis and characterization."
     J. Biochem. 107:262-266(1990).
     PubMed=2361956
[ 3] Huang K., Li Z., Jia Y., Dunaway-Mariano D., Herzberg O.
     "Helix swapping between two alpha/beta barrels: crystal structure of
     phosphoenolpyruvate mutase with bound Mg(2+)-oxalate."
     Structure 7:539-548(1999).
     PubMed=10378273

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