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Heterodimeric integrin adhesion receptors regulate diverse biological processes including angiogenesis, thrombosis and wound healing. The transmembrane-cytoplasmic domains (TMCDs) of integrins play a critical role in controlling activation of these receptors via an inside-out signaling mechanism, but the precise structural basis remains elusive. Here, we present the solution structure of integrin [alpha]IIb[beta]3 TMCD heterodimer, which reveals a right-handed coiled-coil conformation with 2 helices intertwined throughout the transmembrane region. The helices extend into the cytoplasm and form a clasp that differs significantly from a recently published [alpha]IIb[beta]3 TMCD structure. We show that while a point mutation in the clasp interface modestly activates [alpha]IIb[beta]3, additional mutations in the transmembrane interface have a synergistic effect, leading to extensive integrin activation. Detailed analyses and structural comparison with previous studies suggest that extensive integrin activation is a highly concerted conformational transition process, which involves transmembrane coiled-coil unwinding that is triggered by the membrane-mediated alteration and disengagement of the membrane-proximal clasp. Our results provide atomic insight into a type I transmembrane receptor heterocomplex and the mechanism of integrin inside-out transmembrane signaling. NMR | protein structure | transmembrane domain doi/ 10.1073/pnas.0909589106

In polarized epithelial cells, syntaxin 3 localizes to the apical plasma membrane and is involved in membrane fusion of apical trafficking pathways. We show that syntaxin 3 contains a necessary and sufficient apical targeting signal centered around a conserved FMDE motif. Mutation of any of three critical residues within this motif leads to loss of specific apical targeting. Modeling based on the known structure of syntaxin 1 revealed that these residues are exposed on the surface of a three-helix bundle. Syntaxin 3 targeting does not require binding to Munc18b. Instead, syntaxin 3 recruits Munc18b to the plasma membrane. Expression of mislocalized mutant syntaxin 3 in Madin-Darby canine kidney cells leads to basolateral mistargeting of apical membrane proteins, disturbance of tight junction formation, and loss of ability to form an organized polarized epithelium. These results indicate that SNARE proteins contribute to the overall specificity of membrane trafficking in vivo, and that the polarity of syntaxin 3 is essential for epithelial cell polarization.

Author(s): Saurav Misra [1]; Rosa Puertollano [2]; Yukio Kato [2]; Juan S. Bonifacino [2]; James H. Hurley (corresponding author) [1] Specific sorting signals direct transmembrane proteins to the compartments of [...]

The role of lipids in signal transduction with reference to phosphatidylinositol 3-phosphate directing endosomal localization of regulatory proteins is discused. Specific phosphate and hydroxyl group interactions distinguish phosphatidylinositol 3-phosphate from other lipids. The lipid binds to FYVE and PX domains found in intracellular membrane transport/signal transduction proteins and phagocyte proteins, respectively.

The structure of type II-beta phosphatidylinositol phosphate kinase (PIPK) shows a protein kinase ATP-binding core. It indicates that all phosphoinositide kinases are part of one superfamily. The flatness of the membrane-binding site, along with the shallowness of the substrate-binding pocket and its closeness to the membrane indicate that PIPKs phosphyorylate their substrates in situ in membranes. This allows the enzyme to avoid an energetic penalty for removing the substrate from its low-energy conformation within the membrane.

Azithromycin is an antibiotic commonly used for treating respiratory, gastrointestinal infections besides enteric fever, otitis media etc. It’s convenient short duration oral dosing regimens and good tolerability make it a popular drug in routine outpatient settings in primary to tertiary care. Pre-clinical studies have shown immunomodulatory and in vitro activity of azithromycin against SARS CoV-2, which has led to its widespread usage in COVID-19. However, subsequent reviews of observational studies assessing its efficacy in different grades of COVID-19, as well as data from well conducted randomised clinical trials (RCTs) in mild – moderate COVID-19 have shown no or very low quality evidence of benefit of the drug on various clinical outcome parameters. Still, the drug continues to be used indiscriminately in many parts of India for treatment of home isolated patients of mild COVID-19. Such injudicious use in the community should be stopped, otherwise there will be serious adverse consequences of development of resistance to this very useful antibiotic during this pandemic. [ABSTRACT FROM AUTHOR]

Background: The Pharmacovigilance Program of India recommends the use of the World Health Organization-Uppsala Monitoring Centre (WHO-UMC) scale, while many clinicians prefer the Naranjo algorithm for its simplicity. In the present study, we assessed agreement between the two widely used causality assessment scales, that is, the WHO-UMC criteria and the Naranjo algorithm. Materials and Methods: In this study, 842 individual case safety reports were randomly selected from 1000 spontaneously reported forms submitted to the ADR Monitoring Center at a tertiary healthcare Institute in Central India between 2016 and 2018. Two well-trained independent groups performed the causality assessment. One group performed a causality assessment of the 842 ADRs using the WHO-UMC criteria and the other group performed the same using the Naranjo algorithm. The agreement between two ADR causality scales was assessed using the weighted kappa (κ) test. Results: Cohen's kappa coefficient (κ) statistical test was applied between the two scales (WHO-UMC scale and Naranjo algorithm) to find out the agreement between these two scales. "No" agreement was found between the two scales {Kappa statistic with 95% confidence interval = 0.048 (P < 0.001)}. Conclusion: There was no agreement found between the WHO-UMC criteria and the Naranjo algorithm in our study. [ABSTRACT FROM AUTHOR]

Enteroviruses (EVs) are implicated in a wide range of diseases in humans and animals. In this study, a novel enterovirus (enterovirus species G [EVG]) (EVG 08/NC_USA/2015) was isolated from a diagnostic sample from a neonatal pig diarrhea case and identified by using metagenomics and complete genome sequencing. The viral genome shares 75.4% nucleotide identity with a prototypic EVG strain (PEV9 UKG/410/73). Remarkably, a 582-nucleotide insertion, flanked by 3Cpro cleavage sites at the 5' and 3' ends, was found in the 2C/3A junction region of the viral genome. This insertion encodes a predicted protease with 54 to 68% amino acid identity to torovirus (ToV) papain-like protease (PLP) (ToV-PLP). Structural homology modeling predicts that this protease adopts a fold and a catalytic site characteristic of minimal PLP catalytic domains. This structure is similar to those of core catalytic domains of the foot-and-mouth disease virus leader protease and coronavirus PLPs, which act as deubiquitinating and deISGylating (interferon [IFN]-stimulated gene 15 [ISG15]-removing) enzymes on host cell substrates. Importantly, the recombinant ToV-PLP protein derived from this novel enterovirus also showed strong deubiquitination and deISGylation activities and demonstrated the ability to suppress IFN-β expression. Using reverse genetics, we generated a ToV-PLP knockout recombinant virus. Compared to the wild-type virus, the ToV-PLP knockout mutant virus showed impaired growth and induced higher expression levels of innate immune genes in infected cells. These results suggest that ToV-PLP functions as an innate immune antagonist; enterovirus G may therefore gain fitness through the acquisition of ToV-PLP from a recombination event. [ABSTRACT FROM AUTHOR]