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Catalytic Site Atlas Search Results
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Catalytic Site Atlas

CSA LITERATURE entry for 1ci8

E.C. namecarboxylesterase
SpeciesBurkholderia gladioli ()
E.C. Number (IntEnz) 3.1.1.1
CSA Homologues of 1ci8
CSA Entries With UniProtID
CSA Entries With EC Number 3.1.1.1
PDBe Entry 1ci8
PDBSum Entry 1ci8
MACiE Entry 1ci8

Literature Report

IntroductionEstB is an esterase from Burkholderia gladioli with unknown physiological function. It shows very specific activity on short-chain fatty acid esters and triglycerides, and is able to hydrolyse esters of tertiary alcohols such as linalyl acetate. The primary structure exhibits homology to esterases from family VIII; however, catalytic activity is located within the 'beta-lactamase' motif and not the 'esterase' motif. Despite structural similarity with peptidases and beta-lactamases, EstB shows no activity with peptides or beta-lactamases.
MechansimDespite the lack of beta-lactamase activity, the mechanism of EstB is thought to be similar to that of the similar P99 beta-lactamase.
1) Lys 78 and Trp 348 side chains hydrogen bond to Tyr 181, decreasing Tyr 181 pKa and allowing Tyr 181 to exist as the phenolate anion. Tyr 181 can then activate Ser 75 as a nucleophile by deprotonation. 2) The main chain NH groups of Ser 75 and Val 351 can hydrogen bond to the ester substrate, activating the ester bond as an electrophile. 3) Ser 75 attacks the carbon of the substrate ester. A tetrahedral intermediate is formed. Ser 75 and Val 351 main chain NHs stabilise the charge on this intermediate and the preceding transition state. 4) The intermediate collapses, acylating Ser 75. The hydroxyl leaving group is protonated by Tyr 181. 5) Deacylation of the acyl-enzyme is by hydrolysis, the catalytic residues playing the same roles as they did in the acylation steps.
Reaction

Catalytic Sites for 1ci8

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
TyrA181181macie:sideChainTyr 181, as the phenolate anion, is the base that deprotonates Ser 75 for better nucleophilic attack; the proton is transferred to the substrate leaving group. In the deacylation reaction Tyr 181 deprotonates water and transfers the proton to Ser 75.
SerA7575macie:sideChainThe Ser 75 sidechain is the nucleophile, attacking the substrate ester, cleaving the substrate and acylating itself.
The Ser 75 main chain NH activates the substrate towards attack and is part of the oxyanion hole.
SerA7575macie:mainChainAmideThe Ser 75 sidechain is the nucleophile, attacking the substrate ester, cleaving the substrate and acylating itself.
The Ser 75 main chain NH activates the substrate towards attack and is part of the oxyanion hole.
TrpA348348macie:sideChainTrp 348 is proximal to Tyr 181, decreasing the Tyr pKa.
LysA7878macie:sideChainLys 78 is proximal to Tyr 181, decreasing the Tyr pKa.
ValA351351macie:mainChainAmideVal 351 hydrogen bonds to the ester substrate, and acyl-enzyme intermediate, activating them as electrophiles and acting as an oxyanion hole during the transition states and intermediates.

Annotated By Reference To The Literature - Site 2 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
TyrB181181macie:sideChainTyr 181, as the phenolate anion, is the base that deprotonates Ser 75 for better nucleophilic attack; the proton is transferred to the substrate leaving group. In the deacylation reaction Tyr 181 deprotonates water and transfers the proton to Ser 75.
SerB7575macie:sideChainThe Ser 75 sidechain is the nucleophile, attacking the substrate ester, cleaving the substrate and acylating itself.
The Ser 75 main chain NH activates the substrate towards attack and is part of the oxyanion hole.
SerB7575macie:mainChainAmideThe Ser 75 sidechain is the nucleophile, attacking the substrate ester, cleaving the substrate and acylating itself.
The Ser 75 main chain NH activates the substrate towards attack and is part of the oxyanion hole.
TrpB348348macie:sideChainTrp 348 is proximal to Tyr 181, decreasing the Tyr pKa.
LysB7878macie:sideChainLys 78 is proximal to Tyr 181, decreasing the Tyr pKa.
ValB351351macie:mainChainAmideVal 351 hydrogen bonds to the ester substrate, and acyl-enzyme intermediate, activating them as electrophiles and acting as an oxyanion hole during the transition states and intermediates.

Literature References

Notes:
Wagner UG
EstB from Burkholderia gladioli: a novel esterase with a beta-lactamase fold reveals steric factors to discriminate between esterolytic and beta-lactam cleaving activity.
Protein Sci 2002 11 467-478
PubMed: 11847270
Petersen EI
A novel esterase from Burkholderia gladioli which shows high deacetylation activity on cephalosporins is related to beta-lactamases and DD-peptidases.
J Biotechnol 2001 89 11-25
PubMed: 11472796
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