Transient Kinetics of Aminoglycoside Phosphotransferase(30)-Iiia Reveals a Potential Drug Target in the Antibiotic Resistance Mechanism
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FEBS Letters 586 (2012) 4223–4227 journal homepage: www.FEBSLetters.org Transient kinetics of aminoglycoside phosphotransferase(30)-IIIa reveals a potential drug target in the antibiotic resistance mechanism Perrine Lallemand a, Nadia Leban a, Simone Kunzelmann b, Laurent Chaloin a, Engin H. Serpersu c, ⇑ Martin R. Webb b, Tom Barman d, Corinne Lionne a, a Centre d’études d’agents Pathogènes et Biotechnologies pour la Santé (CPBS), UMR 5236 CNRS, University Montpellier I & II, 1919 Route de Mende, 34293 Montpellier Cedex 5, France b Division of Physical Biochemistry, MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom c Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, USA d Volunteer, 8 rue Dom Vaissette, 34000 Montpellier, France article info abstract Article history: Aminoglycoside phosphotransferases are bacterial enzymes responsible for the inactivation of ami- Received 25 September 2012 noglycoside antibiotics by O-phosphorylation. It is important to understand the mechanism of Revised 11 October 2012 enzymes in order to find efficient drugs. Using rapid-mixing methods, we studied the transient Accepted 12 October 2012 kinetics of aminoglycoside phosphotransferase(30)-IIIa. We show that an ADP-enzyme complex is Available online 26 October 2012 the main steady state intermediate. This intermediate interacts strongly with kanamycin A to form Edited by Peter Brzezinski an abortive complex that traps the enzyme in an inactive state. A good strategy to prevent the inac- tivation of aminoglycosides would be to develop uncompetitive inhibitors that interact with this key ADP-enzyme complex. Keywords: Quench flow Ó 2012 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved. Stopped flow Pre-steady state kinetics Uncompetitive inhibition Abortive complex Dead end product 1. Introduction cifically with an intermediate on an enzyme reaction pathway, are especially powerful inhibitors. Thus, he proposes that once the en- Bacterial resistance to antibiotics is a major concern in medical zyme has started to turn over, such inhibitors have a catastrophic treatment. Bacteria have evolved several mechanisms to combat effect on its activity. antibiotics [1]; these are often enzyme systems that are expressed The aminoglycosides are especially susceptible to bacterial upon antibiotic challenge. A strategy for combating bacterial anti- resistance. To protect them against this type of antibiotic, several biotic resistance is to develop drugs that inhibit specifically these bacteria have evolved enzymes that lead to their inactivation by enzymes. This is not an easy matter: as pointed out by Duclert- chemical modification such as N-acetylation, O-adenylation and, Savatier et al. [2], to evaluate the pharmacological or medical in particular, O-phosphorylation [5–7]. importance of an enzyme, one must have a clear understanding Aminoglycoside phosphotransferase(30)-IIIa, APH(30)-IIIa, has a of its function and, especially, its reaction pathway and mechanism broad antibiotic specificity and has been the subject of several of action. As an example, this understanding is important for the structural and steady state kinetic studies [8–12]. With kanamycin rational design of inhibitors of enzymes such as the aminoglyco- A (KanA) and ATP as substrates, this enzyme catalyzes the reaction: side transferases that certain bacteria produce to inactivate amino- KanA þ ATP $ 30-phosphoKanA þ ADP glycoside antibiotics [3]. Cornish-Bowden [4] proposed that uncompetitive inhibitors, that is to say inhibitors that interact spe- In a steady state study in which ADP production was followed by an indirect method using coupled enzyme system, McKay and Wright [10,11] proposed that on the reaction pathway of Abbreviations: APH(30)-IIIa, aminoglycoside phosphotransferase(30)-IIIa (EC APH(30)-IIIa, 30-phosphoKanA is released rapidly followed by a 2.7.1.95); KanA, kanamycin A; MDCC-ParM, ParM labeled with N-[2-(1-maleim- slow release of ADP with kinetics that limit the overall reaction. idyl)ethyl]-7-diethylaminocoumarin-3-carboxamide ⇑ Corresponding author. Fax: +33 (0)434 359 411. Here, we tested this hypothesis by a transient kinetic study on 0 E-mail address: [email protected] (C. Lionne). APH(3 )-IIIa. We exploited two methods: rapid quench flow by 0014-5793/$36.00 Ó 2012 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.febslet.2012.10.027 4224 P. Lallemand et al. / FEBS Letters 586 (2012) 4223–4227 which reaction mixtures are sampled on the millisecond to second pre-incubated with KanA (or ATP), 140 lM NADH, 2 mM time scale [13] and stopped flow which allows reactions to be fol- phospho(enol)pyruvate, 16 U/ml pyruvate kinase and 23 U/ml lac- lowed continuously by optical methods [14]. We show unambigu- tate dehydrogenase was mixed with ATP (or KanA) in the appara- ously that ADP release is the rate limiting step of the reaction tus and the absorbance at 340 nm was measured as a function of pathway and that KanA is at once a substrate and a powerful inhib- time. The concentration of NADH was determined using an extinc- itor because it interacts with the intermediate EÁADP as well as tion coefficient of 6220 MÀ1 cmÀ1 at 340 nm. with the apoenzyme. In the ADP biosensor method, free ADP was measured by the use of an engineered bacterial actin homologue labelled with a single 2. Materials and methods coumarin fluorophore, MDCC-ParM [20]. Fluorescence stopped flow experiments were carried out as in [15]. The excitation wave- 2.1. Materials length was 436 nm and the emission wavelength was >455 nm using a cut-off filter. The excitation and emission slits were 2 nm. KanA sulphate, ADP, ATP (BioXtra), phospho(enol)pyruvic acid APH(30)-IIIa, pre-incubated with 100 lM KanA, was mixed in the and pyruvate kinase/lactic dehydrogenase enzymes from rabbit apparatus with ATP and 30 lM MDCC-ParM and the fluorescence muscle were from Sigma–Aldrich. NADH was from Roche. Recom- was measured as a function of time. The background signal coming binant APH(30)-IIIa from Enterococcus faecalis was produced in from ATP binding to MDCC-ParM was corrected for by measuring Escherichia coli BL21 (DE3) transformed with pET15b plasmid the background fluorescence time course by mixing the same solu- encoding for APH(30)-IIIa with a 6His-tag in N-terminal (from tions but without KanA. The concentration of free ADP was deter- E.H. Serpersu). Production and purification procedures were as in mined by measuring the total fluorescence change (at the end of [15] except that the induction was at 20 °C OVN. The fractions con- the reaction), assuming that all ATP has been converted to ADP taining APH(30)-IIIa were concentrated to 40–60 mg/ml in 20 mM (see below) that is then trapped by MDCC-ParM [20]. Tris–HCl pH 7.5, 100 mM NaCl, 1 mM DTT using an ultra-filtration device (AmiconÒ Ultra-15, cutoff 10 kDa, Millipore). Aliquots of 3. Results 99% pure protein were stored at À20 °C with 50% glycerol and 10 mM DTT. The concentration of APH(30)-IIIa was determined 3.1. Steady state experiments using an extinction coefficient of 48735 MÀ1 cmÀ1 at 280 nm. Except otherwise stated, in the text APH(30)-IIIa refers to the A comparison of the steady state time courses of ADP produc- 6His-tagged recombinant APH(30)-IIIa. As a control, the removal tion measured by the coupled assay and the quench flow methods of the N-terminal 6His-tag was carried out by cleavage of the is shown in Fig. 1. Whereas the time course obtained by the cou- tagged protein with thrombin as in [16]. The catalytic activity pled assay method is linear over 500 s (Fig. 1A), that obtained by was assayed and compared to that of fresh 6His-tagged APH(30)- the quench flow method is not, and only the very initial portion IIIa and of the protein handle in the same way as the one cleaved (Fig. 1B) was used to obtain the steady state rate (kss). The initial (except the presence of thrombin). The 6His-tag and the presence kss determined by the two methods were identical: of sulphate at 0.2 mM (KanA sulphate used) had no effect on the 0.55 ± 0.02 sÀ1 by quench flow, 0.54 ± 0.01 sÀ1 by stopped flow. steady state rates (not shown). The order of mixing of APH with the two substrates had no effect À1 on kss: 0.54 ± 0.01 s when pre-incubating APH with KanA and 2.2. Experimental conditions then mixing with ATP compared to 0.53 ± 0.01 sÀ1 when pre-incu- bating APH with ATP and mixing with KanA (black line and grey Experiments were carried out at 25 °C and in a buffer containing line respectively in Fig. 1B). This suggests that kss is not limited 50 mM Tris–HCl pH 7.5, 40 mM KCl and 1 mM free MgCl2. The con- by the binding of substrates. centration of free Mg2+ used was 1 mM and not 10 mM as in main The non-linearity of the quench flow time course is almost cer- studies with APH(30)-IIIa because 1 mM is rarely inhibitory with ki- tainly due to the accumulation of ADP that may compete with ATP nases and is probably close to the in vivo level [17]. Equimolar con- for the binding to the active site. In the coupled assay method, the centration of MgCl2 was added with ADP and ATP. In the text, ADP ADP is removed as soon as it is formed and converted back to ATP and ATP refer to MgADP and MgATP, respectively.