Cocaine esterase

 

Cocaine esterase (CocE) is from a Rhodococcus strain that lives in the soil of the cocaine producing plant Erythroxylum coca, which is able to use cocaine as its sole carbon and nitrogen source for growth.

CocE hydrolyses cocaine to benzoate and ecgonine methyl ester. Also efficiently hydrolyses cocaethylene, a more potent cocaine metabolite that has been observed in patients who concurrently abuse cocaine and alcohol. Is able to prevent cocaine-induced convulsions and lethality in rat. Hence, CocE is of interest as a cocaine antagonist in acute overdose cases.

CocE belongs to the alpha/beta hydrolase fold superfamily, specifically the CocE/Serine esterase Family. The amino acid sequence of cocaine esterase has a region of similarity with the active serine consensus of X-prolyl dipeptidyl aminopeptidases, suggesting that the cocaine esterase is a serine esterase.

 

Reference Protein and Structure

Sequence
Q9L9D7 UniProt (3.1.1.84) IPR005674 (Sequence Homologues) (PDB Homologues)
Biological species
Rhodococcus sp. MB1 'Bresler 1999' (Bacteria) Uniprot
PDB
1ju3 - BACTERIAL COCAINE ESTERASE COMPLEX WITH TRANSITION STATE ANALOG (1.58 Å) PDBe PDBsum 1ju3
Catalytic CATH Domains
3.40.50.1820 CATHdb 1.10.3020.10 CATHdb (see all for 1ju3)
Click To Show Structure

Enzyme Reaction (EC:3.1.1.84)

cocaine(1+)
CHEBI:60056ChEBI
+
water
CHEBI:15377ChEBI
→
benzoate
CHEBI:16150ChEBI
+
ecgoninium methyl ester(1+)
CHEBI:59908ChEBI
+
hydron
CHEBI:15378ChEBI
Alternative enzyme names: CocE, HCE2, HCE-2, Human carboxylesterase 2,

Enzyme Mechanism

Introduction

CocE is a serine hydrolase employing a chymotrypsin-like Ser-His-Asp catalytic triad and mechanism; the residues are Ser 117, His 287 and Asp 259. The oxyanion hole is formed by Tyr 44 and Tyr 118 main chain. The mechanism occurs as follows:

  1. Asp 259 hydrogen bonds to His 287, increasing His 287 pKa. His 287 can then activate Ser 117 as a nucleophile by deprotonation.
  2. Trp 166 hydrogen bonds to Tyr 44, increasing Tyr 44 pKa. Tyr 44 can then activate the substrate ester bond as an electrophile, along with the main chain amide of Tyr 117 and the helix dipole.
  3. Ser 117 attacks the carbon of the substrate benzoyl ester. A tetrahedral transition state is formed. Tyr 44 and Tyr 117 stabilise the charge on this transition state.
  4. The transition state collapses, acylating Ser 117 with a benzoyl group. The hydroxyl leaving group is presumably protonated by the proton belonging to Ser 117.
  5. Deacylation of the acyl-enzyme is by hydrolysis, the catalytic residues playing the same roles as they did in the acylation steps.

Catalytic Residues Roles

UniProt PDB* (1ju3)
Ser117 Ser117A Acts as the catalytic nucleophile that attacks the substrate ester group, cleaving the substrate and consequently becoming acylated. covalent catalysis, proton shuttle (general acid/base)
Trp166 Trp166A Trp 166 hydrogen bonds to Tyr 44, making Tyr 44 a better stabiliser of the transition state. activator
Asp259 Asp259A Part of the Ser-His-Asp triad. Acts to increase the pKa of the catalytic histidine. Stabilises the resulting charge state. activator, electrostatic stabiliser
His287 His287A Acts as a general acid base, deprotonating the nucleophilic serine and water. The abstracted proton is donated to the hydroxyl leaving groups. proton shuttle (general acid/base)
Tyr44 Tyr44A Helps to stabilise the negatively charged transition states, transition state stabiliser
Ser117 (main-N), Tyr118 (main-N) Ser117A (main-N), Tyr118A (main-N) Main chain amide forms part of the oxyanion hole, activating the substrate towards attack and stabilising the oxyanion transition state. electrostatic stabiliser
*PDB label guide - RESx(y)B(C) - RES: Residue Name; x: Residue ID in PDB file; y: Residue ID in PDB sequence if different from PDB file; B: PDB Chain; C: Biological Assembly Chain if different from PDB. If label is "Not Found" it means this residue is not found in the reference PDB.

Chemical Components

References

  1. Larsen NA et al. (2002), Nat Struct Biol, 9, 17-21. Crystal structure of a bacterial cocaine esterase. DOI:10.1038/nsb742. PMID:11742345.
  2. Rogers CJ et al. (2006), J Am Chem Soc, 128, 15364-15365. Unexpected acetylcholinesterase activity of cocaine esterases. DOI:10.1021/ja066241+. PMID:17131989.
  3. Rogers CJ et al. (2005), J Am Chem Soc, 127, 10016-10017. Toward Cocaine Esterase Therapeutics. DOI:10.1021/ja053086a. PMID:16011362.
  4. Turner JM et al. (2002), Biochemistry, 41, 12297-12307. Biochemical Characterization and Structural Analysis of a Highly Proficient Cocaine Esterase†,‡. DOI:10.1021/bi026131p. PMID:12369817.

Step 1.

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Catalytic Residues Roles

Residue Roles
Tyr44A transition state stabiliser
Trp166A activator
His287A proton shuttle (general acid/base)
Ser117A proton shuttle (general acid/base), covalent catalysis
Ser117A (main-N) electrostatic stabiliser
Tyr118A (main-N) electrostatic stabiliser
Asp259A activator, electrostatic stabiliser

Chemical Components

Step 1.

Contributors

Gemma L. Holliday, Jonathan T. W. Ng