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CSA entry for 1c4t
Original Entry
Title:
Transferase
Compound:
Dihydrolipoamide succinyltransferase
Mutant:
No
UniProt/Swiss-Prot:
P07016-ODO2_ECOLI
EC Class:
2.3.1.61
Other CSA Entries:
Overview of all sites for 1c4t
Homologues of 1c4t
Entries for UniProt/Swiss-Prot: P07016
Entries for EC: 2.3.1.61
Other Databases:
PDB entry: 1c4t
PDBsum entry: 1c4t
UniProt/Swiss-Prot: P07016
IntEnz entry: 2.3.1.61
Literature Report:
Introduction:
The alpha-ketoglutarate dehydrogenase complex (KGDC), also known as the oxoglutarate dehydrogenase complex (OGDC), is composed of multiple copies of three enzymes: oxoglutarate dehydrogenase (E1o), dihydrolipoamide succinyltransferase (E2o), and dihydrolipoamide dehydrogenase (E3o).

The E2o component of the KGDC is a modular protein that is composed of one lipoyl domain at the N-terminus, followed by an E1o- and/or E3o-binding domain, and then by a carboxyl terminal catalytic domain. Although the catalytic domain forms trimers, the enzyme forms the octahedral inner core of the multienzyme complex, an aggregation of 24 subunits arranged with 432 point group symmetry.

The substrate (dihydrolipoamide) is covalently bound to a specific lysine residue in the lipoyl domain. The enzyme catalyses the transfer of a succinyl group from the S-succinyldihydrolipoyl moiety to coenzyme A.
Mechanism:
The first step is the deprotonation of the thiol group of coenzyme A by the active site residue His375. The activated thiolate attacks the carbonyl carbon of the succinylated dihydrolipoyl moiety to form a tetrahedral intermediate, which is stabilised by Thr323'. The collapse of the tetrahedral intermediate results in the succinylation of coenzyme A, and the protonation of the dihydrolipoyl moiety.
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Found by:
Literature reference 

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
HISA 375 376Sidechain
Acid/baseSubstrate
His375 deprotonates the thiol group of coenzyme A to form the nucleophile thiolate.
Evidence from paper Evidence concerns Evidence type
PubMed ID 10739245 Current protein Residue is positioned appropriately (ligand position known)
PubMed ID 10966480 Current protein Conservation of residue
PubMed ID 9677295 Current protein Residue is positioned appropriately (ligand position known)

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
THRC 323 324Sidechain
ElectrostaticSubstrate
Thr323' stabilises the tetrahedral intermediate.
Evidence from paper Evidence concerns Evidence type
PubMed ID 9677295 Current protein Residue is positioned appropriately (ligand position known)
PubMed ID 10739245 Current protein Residue is positioned appropriately (ligand position known)
Notes:

References:
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