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Search The CSA
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Catalytic Site Atlas

CSA LITERATURE entry for 1cl1

E.C. namecystathionine beta-lyase
SpeciesEscherichia coli (Bacteria)
E.C. Number (IntEnz) 4.4.1.8
CSA Homologues of 1cl1There are 139 Homologs
CSA Entries With UniProtID P06721
CSA Entries With EC Number 4.4.1.8
PDBe Entry 1cl1
PDBSum Entry 1cl1
MACiE Entry 1cl1

Literature Report

IntroductionCystathionine beta-lyase is a member of the gamma family of PLP dependent enzymes, and cleaves C(beta)-S bonds in a variety of substrates. The enzyme is important in plant and microbial biosynthesis of methionine, catalysing the cleavage of L-cystathionine to L-homocysteine, pyruvate and ammonia.
MechansimTransaldimation of the substrate, forming a Schiff base with the PLP cofactor follows from the deprotonation of C(alpha) by Tyr111. This external aldimine has the alpha-carboxylate and sulphur atom aligned for proton transfer from the alpha-carbon to the epsilon-N of Lys210. In C-S bond cleavage, Lys210 abstracts the alpha-C proton, forming a quinoid intermediate. The residue's positive charge attracts the anionic phosphate of the coenzyme, aligning Lys210 to donate a proton to the gamma sulphur. Elimination of homocysteine generates the PLP derivative of aminoacrylate, which having accepting a proton from Tyr111 is converted to iminopropionate. This product is hydrolysed to pyruvate and ammonia outside of the enzyme
Reaction

Catalytic Sites for 1cl1

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
TyrA111111macie:sideChainThe residue acts as a base towards the substrate, leading to the formation of the external aldimine. Its pKa is modified through hydrogen bonding interactions with Arg 58. The residue is also thought to stabilise the quinoid intermediate through pi stacking interactions.

Literature References

Notes:
Clausen T
Crystal structure of the pyridoxal-5'-phosphate dependent cystathionine beta-lyase from Escherichia coli at 1.83 A.
J Mol Biol 1996 262 202-224
PubMed: 8831789
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