Observing How Glutathione and S-Hexyl Glutathione Bind to Glutathione S-Transferase from Rhipicephalus (Boophilus) microplus.

Rhipicephalus (Boophilus) microplus is one of the most widespread ticks causing a massive loss to livestock production. The long-term use of acaracides rapidly develops acaracide resistance. In R. microplus, enhancing the metabolic activity of glutathione S-transferase (RmGST) is one of the mechanisms underlying acaracide resistance. RmGST catalyzes the conjugation of glutathione (GSH) to insecticides causing an easy-to-excrete conjugate. The active RmGST dimer contains two active sites (hydrophobic co-substrate binding site (H-site) and GSH binding site (G-site)) in each monomer. To preserve the insecticide efficacy, s-hexyl glutathione (GTX), a GST inhibitor, has been used as a synergist. To date, no molecular information on the RmGST-GSH/GTX complex is available. The insight is important for developing a novel RmGST inhibitor. Therefore, in this work, molecular dynamics simulations (MD) were performed to explore the binding of GTX and GSH to RmGST. GSH binds tighter and sits rigidly inside the G-site, while flexible GTX occupies both active sites. In GSH, the backbone mainly interacts with W8, R43, W46, K50, N59, L60, Q72, and S73, while its thiol group directs to Y7. In contrast, the aliphatic hexyl of GTX protrudes into the H-site and allows a flexible peptide core to form various interactions. Such high GTX flexibility and the protrusion of its hexyl moiety to the H-site suggest the dual role of GTX in preventing the conjugation reaction and the binding of acaracide. This insight can provide a better understanding of an important insecticide-resistance mechanism, which may in turn facilitate the development of novel approaches to tick control.

Intestinal echinococcosis in a dog from Missouri.

CASE DESCRIPTION: A 17-week-old 14.4-kg (31.7-lb) female German Shepherd Dog from Missouri with a history of multiple intermittent episodes of vomiting and diarrhea underwent exploratory celiotomy. CLINICAL FINDINGS: At the time of surgery, the dog was bright, alert, and responsive, with a tender abdomen and palpable mesenteric lymph nodes. Hematologic data revealed mild leukocytosis, mild hypoproteinemia, and mild hypoalbuminemia. Moderate petechiation of the jejunal serosa and prominent mesenteric lymph nodes, but no palpable obstructions, were found during surgery. Jejunal and lymph node biopsies were performed; histologic examination revealed multiple segments of adult cestodes up to 700 µm long in the jejunum. Segments had a scolex and contained approximately 30- to 35-µm-diameter ova, morphologically compatible with Echinococcus spp. Fecal flotation revealed numerous proglottids and ova similar to those recognized histologically. Results of PCR assays confirmed Echinococcus multilocularis of E4 haplotype (a European strain). TREATMENT AND OUTCOME: Praziquantel (5 mg/kg [2.3 mg/lb], SC, once) was administered after surgery; treatments after hospital discharge included praziquantel (10 mg/kg [4.5 mg/lb], PO, once). No proglottids or ova were observed by fecal flotation after the treatments. The dog remained healthy without gastrointestinal signs 1 year later. CLINICAL RELEVANCE: The dog of this report had no travel history outside the state of Missouri. To the authors' knowledge, this is the first report of intestinal E multilocularis infection in a pet dog in the contiguous United States and first detection of a European strain of E multilocularis in this country. Findings suggested possible establishment of a European strain of this zoonotic pathogen in the contiguous United States.

Dynamic and structural insights into tick serpin from Ixodes ricinus.

Ixodid ticks have a crucial impact on people and domestic animals worldwide. These parasites also pose a serious threat to livestock. To date, vaccination of hosts against ticks is a safer, more sustainable alternative to chemical control of ticks and the disease agents they transmit. Because of their roles in tick physiology, serpins (serine protease inhibitors) from tick saliva are among the candidates for anti-tick vaccines. Inhibitory serpins employ a suicide inhibition mechanism to inhibit proteases, where the serpin reactive centre loop (RCL) is cleaved, by the targeted protease, and then inserted into the main ß-sheet of the serpin. This causes a massive conformational change called the 'stressed to relaxed' (S→R) transition, leading to the breakdown of serpin into two regions (core domain and cleaved polypeptide). Recently, the first tick serpin crystal structure from Ixodes ricinus in R-state was reported. We thus employed molecular dynamics simulations to better understand serpin structure and dynamics in atomic detail. Overall, R-state serpin showed high rigidity, especially the core domain. The most flexible region is the terminal of the cleaved polypeptide, due to its high-water exposure, while the rest of the cleaved polypeptide is stably trapped behind the core domain. T363, D367 and N375 are found to play a vital role in protein-protein attachment. This finding can be used to explain the high stability of the R-state serpin at the atomic level and provides insight into this tick serpin which will be useful for rational anti-tick vaccine development. AbbreviationsMDMolecular DynamicsRCLReactive centre loopCommunicated by Ramaswamy H. Sarma.