Biochemical characterization and structural analysis
of a highly proficient cocaine esterase
by
Turner JM, Larsen NA, Basran A, Barbas CF 3rd,
Bruce NC, Wilson IA, Lerner RA.
Department of Molecular Biology,
The Scripps Research Institute,
10550 North Torrey Pines Road,
La Jolla, California 92037, USA.
Biochemistry. 2002 Oct 15;41(41):12297-307

ABSTRACT

The bacterial cocaine esterase, cocE, hydrolyzes cocaine faster than any other reported cocaine esterase. Hydrolysis of the cocaine benzoyl ester follows Michaelis-Menten kinetics with k(cat) = 7.8 s(-1) and K(M) = 640 nM. A similar rate is observed for hydrolysis of cocaethylene, a more potent cocaine metabolite that has been observed in patients who concurrently abuse cocaine and alcohol. The high catalytic proficiency, lack of observable product inhibition, and ability to hydrolyze both cocaine and cocaethylene make cocE an attractive candidate for rapid cocaine detoxification in an emergency setting. Recently, we determined the crystal structure of this enzyme, and showed that it is a serine carboxylesterase, with a catalytic triad formed by S117, H287, and D259 within a hydrophobic active site, and an oxyanion hole formed by the backbone amide of Y118 and the Y44 hydroxyl. The only enzyme previously known to use a Tyr side chain to form the oxyanion hole is prolyl oligopeptidase, but the Y44F mutation of cocE has a more deleterious effect on the specificity rate constant (k(cat)/K(M)) than the analogous Y473F mutation of prolyl oligopeptidase. Kinetic studies on a series of cocE mutants both validate the proposed mechanism, and reveal the relative contributions of active site residues toward substrate recognition and catalysis. Inspired by the anionic binding pocket of the cocaine binding antibody GNC92H2, we found that a Q55E mutation within the active site of cocE results in a modest (2-fold) improvement in K(M), but a 14-fold loss of k(cat). The pH rate profile of cocE was fit to the ionization of two groups (pK(a1) = 7.7; pK(a2) = 10.4) that likely represent titration of H287 and Y44, respectively. We also describe the crystal structures of both S117A and Y44F mutants of cocE. Finally, urea denaturation studies of cocE by fluorescence and circular dichroism show two unfolding transitions (0.5-0.6 M and 3.2-3.7 M urea), with the first transition likely representing pertubation of the active site.

Incas
History
Inca Tea
Insecticide
Oral cocaine
Coke v crack
Cocaethylene
The bacterial junkie: Rhodococcus sp. strain MB1
The crystal structure of cocaine-degrading enzyme

01 02 03 04 05 06 07 08 09 10 11 12
13 14 15 16 17 18 19 20 21 22 23 24

Refs
HOME
HedWeb
cannabis-marijuana.com
Future Opioids
BLTC Research
Wirehead Hedonism
Paradise-Engineering
Utopian Pharmacology
The Hedonistic Imperative
When Is It Best to Take Crack Cocaine?

The Good Drug Guide
The Responsible Parent's Guide To
Healthy Mood Boosters For All The Family