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Search The CSA
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Catalytic Site Atlas

CSA LITERATURE entry for 1pjq

E.C. nameprecorrin-2 dehydrogenase
SpeciesSalmonella typhimurium (Bacteria)
E.C. Number (IntEnz) 1.3.1.76
CSA Homologues of 1pjq
CSA Entries With UniProtID P25924
CSA Entries With EC Number 1.3.1.76
PDBe Entry 1pjq
PDBSum Entry 1pjq
MACiE Entry 1pjq

Literature Report

IntroductionCysG is a trifunctional enzyme which catalyses the formation of sirohaem from uroporphyrin III. Each component can be found independent in other organisms. This catalytic site catalyses two sequential methylation reactions using S-andenosyl-L-methionine (SAM), the first forming precorrin-1 and the second leading to the formation of precorrin-2. It is the first of three steps leading to the formation of siroheme from uroporphyrinogen III.
MechansimThe methyl transfers occur through SN2 type reactions in which the incoming methyl group undergoes stereochemical inversion.
The nitrogen lone pair of ring A activates carbon C2 which subsequently performs nucleophilic attack on the methyl group bound to the sulfur of SAM. Asp248 carboxylate group abstracts a proton from the tetrapyrrole ring. Lys270 could serve as a general acid to promote tautomerization of the tetrapyrrole, facilitating proton abstraction by Asp248. The resultant rearrangement of double bonds (C1-NH+ and C3-C4 to C20-C1 and C4-C5 respectively) forms precorrin-1.
The resultant S-adenosyl-L-homocystine (SAH) and precorrin-1 are lost from the active site followed by binding of new SAM and precorrin-1 in a new orientation placing C7 in the correct position for methylation. The above process is repeated at C7, forming a second SAH and precorrin-2.
Reaction

Catalytic Sites for 1pjq

Annotated By Reference To The Literature - Site 3 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
AspA248248macie:sideChainAbstracts a proton from the substrate to cause double bond rearrangement forming precorrin-1. Then abstracts a proton from the substrate to cause double bond rearrangement forming precorrin-2.
LysA270270macie:sideChainActs as a general acid to aid proton abstraction by Asp248.
MetA382382macie:sideChainMay function to destabilize the charged S of SAM thus favouring formation of SAH.

Annotated By Reference To The Literature - Site 4 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
AspB248248macie:sideChainAbstracts a proton from the substrate to cause double bond rearrangement forming precorrin-1. Then abstracts a proton from the substrate to cause double bond rearrangement forming precorrin-2.
MetB382382macie:sideChainMay function to destabilize the charged S of SAM thus favouring formation of SAH.
LysB270270macie:sideChainActs as a general acid to aid proton abstraction by Asp248.

Literature References

Notes:
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