The nonstructural protein 5 of coronaviruses antagonizes GSDMD-mediated pyroptosis by cleaving and inactivating its pore-forming p30 fragment

Coronaviruses (CoV) are a family of RNA viruses that typically cause respiratory, enteric and hepatic diseases in animals and humans. Here, we used porcine epidemic diarrhea virus (PEDV) as a model of coronaviruses (CoVs) to illustrate the reciprocal regulation between CoVs infection and pyroptosis. For the first time, we clarified the molecular mechanism of porcine Gasdermin D (pGSDMD)-mediated pyroptosis and demonstrated that amino acids T239 and F240 within pGSDMD-p30 are critical for pyroptosis. Furthermore, 3C-like protease Nsp5 from SARS-CoV-2, MERS-CoV, PDCoV and PEDV can cleave human/porcine GSDMD at the Q193-G194 junction upstream of the caspase-1 cleavage site to produce two fragments which fail to trigger pyroptosis or inhibit viral replication. Thus, we provide clear evidence that coronoviruses may utilize viral Nsp5-GSDMD pathway to help their host cells escaping from pyroptosis, protecting the replication of the virus during the initial period, which suggest an important strategy for coronoviruses infection and sustain.

A serine/threonine phosphatase 1 of Streptococcus suis type 2 is an important virulence factor

Streptococcus suis is regarded as one of the major pathogens of pigs, and Streptococcus suis type 2 (SS2) is considered a zoonotic bacterium based on its ability to cause meningitis and streptococcal toxic shock-like syndrome in humans. Many bacterial species contain genes encoding serine/threonine protein phosphatases (STPs) responsible for dephosphorylation of their substrates in a single reaction step. This study investigated the role of stp1 in the pathogenesis of SS2. An isogenic stp1 mutant (Δstp1) was constructed from SS2 strain ZJ081101. The Δstp1 mutant exhibited a significant increase in adhesion to HEp-2 and bEnd.3 cells as well as increased survival in RAW264.7 cells, as compared to the parent strain. Increased survival in macrophage cells might be related to resistance to reactive oxygen species since the Δstp1 mutant was more resistant than its parent strain to paraquat-induced oxidative stress. However, compared to parent strain virulence, deletion of stp1 significantly attenuated virulence of SS2 in mice, as shown by the nearly double lethal dose 50 value and the lower bacterial load in organs and blood in the murine model. We conclude that Stp1 has an essential role in SS2 virulence.

Membrane protein characterization by photoactivatable localization microscopy / 生物工程学报

The on-site labeling and localization tracking of membrane proteins in pathogenic bacteria are tedious work. In order to develop a novel protein labeling technology at super resolution level (nanometer scale) using the photoactivatable localization microscopy (PALM), the chimeric protein of the outer membrane protein A (OmpA) of Mycobacterium tuberculosis and the photoactivatable mEos2m protein were expressed in the non-pathogenic Mycobacterium smegmatis. The recombinant bacteria were fixed on slide, activated by 405 nm laser and subject to PALM imaging to capture photons released by the fusion protein. Meanwhile, colony and cell morphology were visualized under regular fluorescent stereomicroscope and upright fluorescent microscope to characterize fluorescence conversion and protein localization. The fusion proteins formed a "belt"-like structure on cell membrane of M. smegmatis under PALM, providing direct evidence of on-site imaging of membrane proteins. Expression of fusion protein did not compromise the localization properties of OmpA. Thus, mEos2m could be used as a labeling probe to track localizations of non-oligomer oriented membrane proteins. This indicates non-pathogenic M. smegmatis could be served as a model strain to characterize the function and localization of the proteins derived from pathogenic M. tuberculosis. This is the first report using PALM to characterize localization of membrane proteins.

Analysis of Major Virulence Genes in Vibrio Parahaemolyticus Isolates from Coastal Areas in Zhejiang Province / 微生物学通报

Several aquatic species and their enviroments were examined for presence of Vibrio parahaemo-lyticus between 2007 and 2008 in the coastal areas in Zhejiang province, and some virulence-related genes such as tdh, trh, ureC and vscC2 were investigated from the isolates. V. parahaemolyticus was recovered from 70% of the samples tested (395/566). The genes tdh, trh and ureC existed in 10.1%, 20.0% and 11.1% respectively from 395 isolates. Among the 40 tdh-positive isolates, 32.5% harbored the vscC2 gene, one of the type three secretion system 2 (T3SS2) gene family. Thirty-eight of the 40 tdh-positive isolates were positive for the Kanagawa phenomenon. Out of 44 trh-and-ureC-positive isolates, only six exhibited urease phenotype. Overall, this study reveals the significant prevalence of Vibrio parahaemolyticus in seafoods and their habitats with high diversity of virulence genes. Representative V. parahaemolyticus isolates could beused for further investigation into their pathongenecity, functional genomics, and molecular evolution.

Identification of Listeria monocytogenes by multiplux PCR / 中华检验医学杂志

Objective To develop a rapid and specific method for identification of listerial species and differentiation of Listeria monocytogenes。 Method Primers targeting the iap and hly genes specific for listerial species and L monocytogenes were designed。 The dulplex PCR and triplex PCR were compared for their ability to identify and differentiate the listerial species。 Results Both dulplex PCR and triplex PCR are specific to all listerial reference strains. The dulplex-PCR could not identify some of the L. monocytogenes isolates while the triplex PCR did. Conclusion The triplex PCR method could be used not only for identification of listerial species but also for differentiation of L. monocytogenes from the mixed listerial suspensions.