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Infection and Immunity, June 2008, p. 2512-2519, Vol. 76, No. 6
0019-9567/08/$08.00+0     doi:10.1128/IAI.01606-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Dominant Role of Paraoxonases in Inactivation of the Pseudomonas aeruginosa Quorum-Sensing Signal N-(3-Oxododecanoyl)-L-Homoserine Lactone

Department of Internal Medicine, Division of Epidemiology, The University of Texas Southwestern Medical Center, Dallas, Texas 75390,¹ Department of Pharmacology, Johannes Gutenberg University, Mainz, Germany,² Department of Chemistry, University of Texas at Dallas, Richardson, Texas 75083,³ Department of Metabolism, WIL Research Laboratories, LLC, Ashland, Ohio 44805⁴

Received 5 December 2007/ Returned for modification 8 January 2008/ Accepted 5 March 2008

The pathogenic bacterium Pseudomonas aeruginosa causes serious infections in immunocompromised patients. N-(3-Oxododecanoyl)-L-homoserine lactone (3OC12-HSL) is a key component of P. aeruginosa's quorum-sensing system and regulates the expression of many virulence factors. 3OC12-HSL was previously shown to be hydrolytically inactivated by the paraoxonase (PON) family of calcium-dependent esterases, consisting of PON1, PON2, and PON3. Here we determined the specific activities of purified human PONs for 3OC12-HSL hydrolysis, including the common PON1 polymorphic forms, and found they were in the following order: PON2 >> PON1_192R > PON1_192Q > PON3. PON2 exhibited a high specific activity of 7.6 ± 0.4 µmols/min/mg at 10 µM 3OC12-HSL, making it the best PON2 substrate identified to date. By use of class-specific inhibitors, approximately 85 and 95% of the 3OC12-HSL lactonase activity were attributable to PON1 in mouse and human sera, respectively. In mouse liver homogenates, the activity was metal dependent, with magnesium- and manganese-dependent lactonase activities comprising 10 to 15% of the calcium-dependent activity. In mouse lung homogenates, all of the activity was calcium dependent. The calcium-dependent activities were irreversibly inhibited by extended EDTA treatment, implicating PONs as the major enzymes inactivating 3OC12-HSL. In human HepG2 and EA.hy 926 cell lysates, the 3OC12-HSL lactonase activity closely paralleled the PON2 protein levels after PON2 knockdown by small interfering RNA treatment of the cells. These findings suggest that PONs, particularly PON2, could be an important mechanism by which 3OC12-HSL is inactivated in mammals.

Published ahead of print on 17 March 2008.

Editor: B. A. McCormick

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