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Catalytic Site Atlas

CSA LITERATURE entry for 1ozh

E.C. nameacetolactate synthase
SpeciesKlebsiella pneumoniae ()
E.C. Number (IntEnz) 2.2.1.6
CSA Homologues of 1ozh
CSA Entries With UniProtID P27696
CSA Entries With EC Number 2.2.1.6
PDBe Entry 1ozh
PDBSum Entry 1ozh
MACiE Entry 1ozh

Literature Report

IntroductionAcetolactate synthase (ALS) isolated from Klebsiella pneumoniae is a ThDP-dependent enzyme that catalyses the reaction of two molecules of pyruvate to 2-acetolactate and carbon dioxide. This reaction is important in butanediol fermentation.
Unlike acetohydroxyacid synthase, which catalyses the same reaction in other organisms, ALS does not contain a molecule of non-catalytic FAD. Another oddity is that the N-3 of ALS is thought to be pyramidal while all other ThDP-dependent enzymes possess a planar N-3. This is thought to account for the unusually high kcat of ALS by increasing the acidity of the C-2 proton.

MechansimThe thiazolium ring of ThDP ionises at the C-2 position with the 4'-amino group acting as the base (activated by the interaction between a conserved glutamate residue and N-1'). The negative charge on C-2 is stabilised by forming a covalent bond to the 4'-amino group. There is nucleophilic attack on the C-2'' of the carbonyl of pyruvate by C-2 to form tricyclic lactyl-ThDP. Subsequent decarboxylation produces carbon dioxide and an enamine with no bond between C-2 and the 4'-amino group. This bond reforms and causes the C-2'' to act as the nucleophile in the attack on the carbonyl of a second pyruvate. The reformation of the carbonyl at C-2'' breaks the C-2 – C-2'' bond, releasing acetolactate and returning ThDP to its ionised form.

Reaction

Catalytic Sites for 1ozh

Annotated By Reference To The Literature - Site 5 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
MetA422422macie:sideChainMet422 projects between the thiazolium and methylaminopyrimidine rings of ThDP and forces the cofactor into a V conformation. This positions the 4'-amino group close to C-2 which is necessary for the deprotonation of C-2 and the subsequent formation of the tricyclic form of ThDP.
MetA394394macie:sideChainThe backbone carbonyl is able to stabilise a positive charge on the S-1 of ThDP, thus stabilising the form in which N-3 is pyramidal and leading to a more acidic C-2 proton.

Annotated By Reference To The Literature - Site 6 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
MetB422422macie:sideChainMet422 projects between the thiazolium and methylaminopyrimidine rings of ThDP and forces the cofactor into a V conformation. This positions the 4'-amino group close to C-2 which is necessary for the deprotonation of C-2 and the subsequent formation of the tricyclic form of ThDP.
MetB394394macie:sideChainThe backbone carbonyl is able to stabilise a positive charge on the S-1 of ThDP, thus stabilising the form in which N-3 is pyramidal and leading to a more acidic C-2 proton.

Annotated By Reference To The Literature - Site 7 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
MetC422422macie:sideChainMet422 projects between the thiazolium and methylaminopyrimidine rings of ThDP and forces the cofactor into a V conformation. This positions the 4'-amino group close to C-2 which is necessary for the deprotonation of C-2 and the subsequent formation of the tricyclic form of ThDP.
MetC394394macie:sideChainThe backbone carbonyl is able to stabilise a positive charge on the S-1 of ThDP, thus stabilising the form in which N-3 is pyramidal and leading to a more acidic C-2 proton.

Annotated By Reference To The Literature - Site 8 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
MetD422422macie:sideChainMet422 projects between the thiazolium and methylaminopyrimidine rings of ThDP and forces the cofactor into a V conformation. This positions the 4'-amino group close to C-2 which is necessary for the deprotonation of C-2 and the subsequent formation of the tricyclic form of ThDP.
MetD394394macie:sideChainThe backbone carbonyl is able to stabilise a positive charge on the S-1 of ThDP, thus stabilising the form in which N-3 is pyramidal and leading to a more acidic C-2 proton.

Literature References

Notes:The identity of the conserved glutamate involved in ThDP ionisation is currently unknown.
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