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Antimicrobial Agents and Chemotherapy, December 2001, p. 3509-3516, Vol. 45, No. 12
Dipartimento di Scienze e Tecnologie
Biomediche, Università di L'Aquila, I-67100
L'Aquila,1 and Dipartimento di Biologia
Molecolare, Sezione di Microbiologia, Università di Siena,
I-53100 Siena,2 Italy, and
Laboratoire d'Enzymologie & Centre d'Ingénierie des
Protéines, Institut de Chimie, Université de
Liège, Sart Tilman, B-4000 Liège, Belgium3
Received 26 February 2001/Returned for modification 23 June
2001/Accepted 23 September 2001
A class D
0066-4804/01/$04.00+0 DOI: 10.1128/AAC.45.12.3509-3516.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Characterization of OXA-29 from Legionella
(Fluoribacter) gormanii: Molecular Class D
-Lactamase with Unusual Properties
-lactamase determinant was isolated from the genome of
Legionella (Fluoribacter) gormanii
ATCC 33297T. The enzyme, named OXA-29, is quite divergent
from other class D
-lactamases, being more similar (33 to 43% amino
acid identity) to those of groups III (OXA-1) and IV (OXA-9, OXA-12,
OXA-18, and OXA-22) than to other class D enzymes (21 to 24% sequence identity). Phylogenetic analysis confirmed the closer ancestry of
OXA-29 with members of the former groups. The OXA-29 enzyme was
purified from an Escherichia coli strain overexpressing the gene via a T7-based expression system by a single ion-exchange chromatography step on S-Sepharose. The mature enzyme
consists of a 28.5-kDa polypeptide and exhibits an isoelectric pH of
>9. Analysis of the kinetic parameters of OXA-29 revealed efficient activity (kcat/Km
ratios of >105 M
1 · s
1)
for several penam compounds (oxacillin, methicillin, penicillin G,
ampicillin, carbenicillin, and piperacillin) and also for cefazolin and
nitrocefin. Oxyimino cephalosporins and aztreonam were also hydrolyzed,
although less efficiently
(kcat/Km ratios of
around 103 M
1 · s
1).
Carbapenems were neither hydrolyzed nor inhibitory. OXA-29 was
inhibited by BRL 42715 (50% inhibitory concentration
[IC50], 0.44 µM) and by tazobactam (IC50,
3.2 µM), but not by clavulanate. It was also unusually resistant to
chloride ions (IC50, >100 mM). Unlike OXA-10, OXA-29 was
apparently found as a dimer both in diluted solutions and in the
presence of EDTA. Its activity was either unaffected or inhibited by
divalent cations. OXA-29 is a new class D
-lactamase that exhibits
some unusual properties likely reflecting original structural and
mechanistic features.
*
Corresponding author. Mailing address: Dipartimento di
Biologia Molecolare, Sez. di Microbiologia, Università di Siena,
Policlinico "Le Scotte," 53100 Siena, Italy. Phone: 39 0577 233455. Fax: 39 0577 233325. E-mail: rossolini{at}unisi.it.
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