Acinetobacter baumannii is a multidrug resistant pathogen that infects more than 12 000 patients each year in the US. Much of the resistance to β-lactam antibiotics in Acinetobacter spp. is mediated by class C β-lactamases known as Acinetobacter-derived cephalosporinases (ADCs). ADCs are unaffected by clinically used β-lactam-based β-lactamase inhibitors. In this study, five boronic acid transition state analog inhibitors (BATSIs) were evaluated for inhibition of the class C cephalosporinase ADC-7. Our goal was to explore the properties of BATSIs designed to probe the R1 binding site. K_i values ranged from low micromolar to subnanomolar, and circular dichroism (CD) demonstrated that each inhibitor stabilizes the β-lactamase–inhibitor complexes. Additionally, X-ray crystal structures of ADC-7 in complex with five inhibitors were determined (resolutions from 1.80 to 2.09 Å). In the ADC-7/CR192 complex, the BATSI with the lowest K_i (0.45 nM) and greatest ΔT_m (+9 °C), a trifluoromethyl substituent, interacts with Arg340. Arg340 is unique to ADCs and may play an important role in the inhibition of ADC-7. The ADC-7/BATSI complexes determined in this study shed light into the unique recognition sites in ADC enzymes and also offer insight into further structure-based optimization of these inhibitors.

中文翻译：

---

硼酸作为不动杆菌衍生的头孢菌素酶-7（一种独特的C类β-内酰胺酶）抑制剂的基于结构的分析

鲍曼不动杆菌是一种耐多药病原体，在美国每年感染超过12000名患者。不动杆菌属中对β-内酰胺抗生素的大部分抗药性。Cβ-内酰胺酶由称为不动杆菌的头孢菌素酶（ADC）的C类β-内酰胺酶介导。ADC不受临床使用的基于β-内酰胺的β-内酰胺酶抑制剂的影响。在这项研究中，评估了五种硼酸过渡态类似物抑制剂（BATSI）对C类头孢菌素酶ADC-7的抑制作用。我们的目标是探索旨在探测R1结合位点的BATSI的特性。ķ_我值范围从低微摩尔到亚纳摩尔，圆二色性（CD）证明每种抑制剂都能稳定β-内酰胺酶-抑制剂复合物。另外，测定了与五种抑制剂复合的ADC-7的X射线晶体结构（分辨率为1.80至2.09Å）。在ADC-7 / CR192复合物中，具有最低K _i（0.45 nM）和最大ΔT _m（+9°C）（三氟甲基取代基）的BATSI与Arg340相互作用。Arg340是ADC特有的，可能在抑制ADC-7中起重要作用。在这项研究中确定的ADC-7 / BATSI复合物揭示了ADC酶中独特的识别位点，也为深入了解这些抑制剂的基于结构的优化提供了见识。