Crystal structures of KPC-2 β-lactamase in complex with 3-nitrophenyl boronic acid and the penam sulfone PSR-3-226

Class A carbapenemases are a major threat to the potency of carbapenem antibiotics. A widespread carbapenemase, KPC-2, is not easily inhibited by β-lactamase inhibitors (i.e., clavulanic acid, sulbactam, and tazobactam). To explore different mechanisms of inhibition of KPC-2, we determined the crystal structures of KPC-2 with two β-lactamase inhibitors that follow different inactivation pathways and kinetics. The first complex is that of a small boronic acid compound, 3-nitrophenyl boronic acid (3-NPBA), bound to KPC-2 with 1.62-Å resolution. 3-NPBA demonstrated a K_m value of 1.0 ± 0.1 μM (mean ± standard error) for KPC-2 and blocks the active site by making a reversible covalent interaction with the catalytic S70 residue. The two boron hydroxyl atoms of 3-NPBA are positioned in the oxyanion hole and the deacylation water pocket, respectively. In addition, the aromatic ring of 3-NPBA provides an edge-to-face interaction with W105 in the active site. The structure of KPC-2 with the penam sulfone PSR-3-226 was determined at 1.26-Å resolution. PSR-3-226 displayed a K_m value of 3.8 ± 0.4 μM for KPC-2, and the inactivation rate constant (k_inact) was 0.034 ± 0.003 s⁻¹. When covalently bound to S70, PSR-3-226 forms a trans-enamine intermediate in the KPC-2 active site. The predominant active site interactions are generated via the carbonyl oxygen, which resides in the oxyanion hole, and the carboxyl moiety of PSR-3-226, which interacts with N132, N170, and E166. 3-NPBA and PSR-3-226 are the first β-lactamase inhibitors to be trapped as an acyl-enzyme complex with KPC-2. The structural and inhibitory insights gained here could aid in the design of potent KPC-2 inhibitors.     

Bronchial and bronchiolar fibrosis in rats exposed to 2,3-pentanedione vapors: implications for bronchiolitis obliterans in humans

2,3-Pentanedione (PD) is a component of artificial butter flavorings. The use of PD is increasing since diacetyl, a major butter flavorant, was associated with bronchiolitis obliterans (BO) in workers and has been removed from many products. Because the toxicity of inhaled PD is unknown, these studies were conducted to characterize the toxicity of inhaled PD across a range of concentrations in rodents. Male and female Wistar-Han rats and B6C3F1 mice were exposed to 0, 50, 100, or 200 ppm PD 6 h/d, 5 d/wk for up to 2 wk. Bronchoalveolar lavage fluid (BALF) was collected after 1, 3, 5, and 10 exposures, and histopathology was evaluated after 12 exposures. MCP-1, MCP-3, CRP, FGF-9, fibrinogen, and OSM were increased 2- to 9-fold in BALF of rats exposed for 5 and 10 days to 200 ppm. In mice, only fibrinogen was increased after 5 exposures to 200 ppm. The epithelium lining the respiratory tract was the site of toxicity in all mice and rats exposed to 200 ppm. Significantly, PD also caused both intraluminal and intramural fibrotic airway lesions in rats. The histopathological and biological changes observed in rats raise concerns that PD inhalation may cause BO in exposed humans.     

A practical clinical method to quantify language lateralization in fMRI using whole-brain analysis

Surgery is often the only effective treatment for intractable epilepsy, but its benefits must be balanced by potential disruption of eloquent cortical functions. Wada test is the standard technique to lateralize language before surgery; however, it is invasive and associated with complications. fMRI provides an attractive noninvasive alternative, which has been previously shown to correlate with Wada results. However this correlation is imperfect since standard fMRI laterality indices are dependent on a particular arbitrary statistical threshold used in the data processing. We report a novel automated, threshold-independent fMRI methodology to assess language lateralization, which we hypothesize provides a robust and unbiased pre-operative assessment. This hemispheric histogram analysis method can accurately interrogate language lateralization, as validated against the Wada test. Fifty-nine subjects with intractable epilepsy received preoperative evaluation for language lateralization using fMRI. fMRI data then were analyzed using a novel automated threshold-independent method for determining language lateralization. The methodology generated a lateralization score based on hemispheric activation of language areas and a quality index based on multiple factors, including patient motion and signal-to-noise characteristics. Lateralization scores were compared to Wada test results (51 patients), direct cortical stimulation (3 patients), and subdural grid stimulation (5 patients). Data sets were used to generate a probability score for language lateralization for each subject. The lateralization scores correlated well with the objective measures of language lateralization (r(2)=0.46). Cumulative historical data were utilized to prospectively determine probabilities of language lateralization for individual patients. In conclusion, hemispheric language lateralization can be accurately determined using a novel objective and automated methodology that calculates language lateralization in a threshold-independent manner and can be used to determine the probability of language dominance in individual patients.     

Dimensionally Specific Attention Capture in Birds Performing Auditory Streaming Task

Journal of the Association for Research in Otolaryngology - Previous studies in budgerigars (Melopsittacus undulatus) have indicated that they experience attention capture in a qualitatively...     

An Introduction to the Residency Application Process

Emergency medicine (EM) is a swiftly developing yet still relatively young discipline. We are going to present in the Medical Student Forum section of the Journal of Emergency Medicine several article series covering the key topics that medical students interested in emergency medicine will find helpful. This article introduces the topics that will be tackled in the first compilation of articles dealing with the residency application process.     

土拨鼠白细胞介素15的克隆、表达和活性分析

目的对土拨鼠白细胞介素15（woodchuck interleukin 15，wIL-15）分子进行克隆、表达并鉴定其活性，为进一步研究IL-15在嗜肝病毒感染中的作用以及评价IL-15用于治疗慢性HBV感染奠定基础。方法用IL-15的保守引物将wIL-15基因克隆、测序并进行分析，构建wIL-15的原核表达质粒，在大肠杆菌中表达，分离纯化后用淋巴细胞增殖试验检测其生物学活性。结果wIL-15的完整编码序列为489nt（与其他哺乳动物IL-15编码序列的同源性高达78％～87％），编码162AA长度的前体蛋白（与其他哺乳动物IL-15蛋白的同源性高达70％～80％），其信号肽为N端的48AA，成熟蛋白由114AA组成。土拨鼠IL-15与灵长动物IL-15的同源性高于啮齿动物。带有His-tag的成熟蛋白，可以在大肠杆菌中表达，分离纯化后，可以刺激Con A活化的小鼠脾细胞和土拨鼠PBMC增殖（其SI值可高达10以上），并存在明显的剂量依赖性。结论（1）wIL-15与其他哺乳动物IL-15高度同源，并且与灵长类动物的IL-15更接近。（2）wIL-15可以在大肠杆菌中表达，并在纯化后能刺激小鼠和土拨鼠淋巴细胞增殖，表现出较好的生物学活性。