Structural and Kinetic Insights into the 鈥淐eftazidimase鈥?Behavior of the Extended-Spectrum 尾-Lactamase CTX-M-96
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- 作者：Barbara Ghiglione ; Mar铆a Margarita Rodr铆guez ; Rapha毛l Herman ; Lucrecia Curto ; Milena Dropa ; Fabrice Bouillenne ; Fr茅d茅ric Kerff ; Moreno Galleni ; Paulette Charlier ; Gabriel Gutkind ; Eric Sauvage ; Pablo Power
- 刊名：Biochemistry
- 出版年：2015
- 出版时间：August 18, 2015
- 年：2015
- 卷：54
- 期：32
- 页码：5072-5082
- 全文大小：458K
- ISSN：1520-4995
文摘
Diversification of the CTX-M 尾-lactamases led to the emergence of variants responsible for decreased susceptibility to ceftazidime, like the Asp240Gly-harboring 鈥渃eftazidimases鈥? We solved the crystallographic structure of the Asp240Gly variant CTX-M-96 at 1.2 脜 and evaluated the role of Asp240 in the activity toward oxyimino-cephalosporins through simulated models and kinetics. There seem to be subtle changes in the conformation of the active site cavity of CTX-M-96, compared to enzyme variants harboring the Asp240, and these small rearrangements could be due to localized shifts in the environment of the 尾3 strand. According to the crystallographic evidence, CTX-M-96 presents a 鈥渃ompact鈥?active site, which in spite of its reduced cavity seems to allow the proper interaction with oxyimino-cephalosporins, as suggested by simulated models. The term 鈥渃eftazidimases鈥?that is currently applied for the Asp240Gly-harboring CTX-M variants should be used carefully. Structural differences between CTX-M harboring the Asp240Gly mutation (and also probably others like those at Pro167) do not seem to be conclusive to determine the 鈥渃eftazidimase鈥?behavior observed in vivo, which is in turn partially supported by the mild improvement in the catalytic efficiency toward ceftazidime by CTX-M-96 and similar enzymes, compared to 鈥減arental鈥?Asp240-harboring variants. In addition, it is observed that alterations in OmpF expression could act synergistically with CTX-M-96 for yielding clinical resistance toward ceftazidime. We therefore propose that the observed resistance in vivo is due to the sum of synergic mechanisms, and the term 鈥渃efotaximases associated with ceftazidime resistance鈥?could be conveniently used to describe CTX-M harboring the Asp240Gly substitution.