2OGT

Crystal Structure of the Geobacillus Stearothermophilus Carboxylesterase EST55 at pH 6.8

Summary for 2OGT

• Entry DOI: 10.2210/pdb2ogt/pdb
• Related: 2OGS
• Descriptor: Thermostable carboxylesterase Est50, IODIDE ION, GLYCEROL, ... (4 entities in total)
• Functional Keywords: carboxylesterase, alpha/beta hydrolase, hydrolase
• Biological source: Geobacillus stearothermophilus
• Total number of polymer chains: 1
• Total formula weight: 55236.17

Authors

Liu, P.,Ewis, H.E.,Tai, P.C.,Lu, C.D.,Weber, I.T. (deposition date: 2007-01-08, release date: 2007-02-13, Last modification date: 2023-08-30)

Primary citation

Liu, P.,Ewis, H.E.,Tai, P.C.,Lu, C.D.,Weber, I.T.
Crystal Structure of the Geobacillus stearothermophilus Carboxylesterase Est55 and Its Activation of Prodrug CPT-11.
J.Mol.Biol., 367:212-223, 2007

PubMed Abstract: Several mammalian carboxylesterases were shown to activate the prodrug irinotecan (CPT-11) to produce 7-ethyl-10-hydroxycamptothecin (SN-38), a topoisomerase inhibitor used in cancer therapy. However, the potential use of bacterial carboxylesterases, which have the advantage of high stability, has not been explored. We present the crystal structure of the carboxyesterase Est55 from Geobacillus stearothermophilus and evaluation of its enzyme activity on CPT-11. Crystal structures were determined at pH 6.2 and pH 6.8 and resolution of 2.0 A and 1.58 A, respectively. Est55 folds into three domains, a catalytic domain, an alpha/beta domain and a regulatory domain. The structure is in an inactive form; the side-chain of His409, one of the catalytic triad residues, is directed away from the other catalytic residues Ser194 and Glu310. Moreover, the adjacent Cys408 is triply oxidized and lies in the oxyanion hole, which would block the binding of substrate, suggesting a regulatory role. However, Cys408 is not essential for enzyme activity. Mutation of Cys408 showed that hydrophobic side-chains were favorable, while polar serine was unfavorable for enzyme activity. Est55 was shown to hydrolyze CPT-11 into the active form SN-38. The mutant C408V provided a more stable enzyme for activation of CPT-11. Therefore, engineered thermostable Est55 is a candidate for use with irinotecan in enzyme-prodrug cancer therapy.

PubMed: 17239398
DOI: 10.1016/j.jmb.2006.12.067

Experimental method

X-RAY DIFFRACTION (1.58 Å)