Phosphatidic acid-mediated binding and mammalian cell internalization of the Vibrio cholerae cytotoxin MakA

Vibrio cholerae is a noninvasive intestinal pathogen extensively studied as the causative agent of the human disease cholera. Our recent work identified MakA as a potent virulence factor of V. cholerae in both Caenorhabditis elegans and zebrafish, prompting us to investigate the potential contribution of MakA to pathogenesis also in mammalian hosts. In this study, we demonstrate that the MakA protein could induce autophagy and cytotoxicity of target cells. In addition, we observed that phosphatidic acid (PA)-mediated MakA-binding to the host cell plasma membranes promoted macropinocytosis resulting in the formation of an endomembrane-rich aggregate and vacuolation in intoxicated cells that lead to induction of autophagy and dysfunction of intracellular organelles. Moreover, we functionally characterized the molecular basis of the MakA interaction with PA and identified that the N-terminal domain of MakA is required for its binding to PA and thereby for cell toxicity. Furthermore, we observed that the ΔmakA mutant outcompeted the wild-type V. cholerae strain A1552 in the adult mouse infection model. Based on the findings revealing mechanistic insights into the dynamic process of MakA-induced autophagy and cytotoxicity we discuss the potential role played by the MakA protein during late stages of cholera infection as an anti-colonization factor.     

Investigation of the Greek ancestry of populations from northern Pakistan

Three populations from northern Pakistan, the Burusho, Kalash, and Pathan, claim descent from soldiers left behind by Alexander the Great after his invasion of the Indo-Pak subcontinent. In order to investigate their genetic relationships, we analyzed nine Alu insertion polymorphisms and 113 autosomal microsatellites in the extant Pakistani and Greek populations. Principal component, phylogenetic, and structure analyses show that the Kalash are genetically distinct, and that the Burusho and Pathan populations are genetically close to each other and the Greek population. Admixture estimates suggest a small Greek contribution to the genetic pool of the Burusho and Pathan and demonstrate that these two northern Pakistani populations share a common Indo-European gene pool that probably predates Alexanders invasion. The genetically isolated Kalash population may represent the genetic pool of ancestral Eurasian populations of Central Asia or early Indo-European nomadic pastoral tribes that became sequestered in the valleys of the Hindu Kush Mountains.     

Towards thermally stable cyclophanediene-dihydropyrene photoswitches

Cyclophanediene dihydropyrenes (CPD-DHP) are photochromic compounds because they change their color by irradiation with lights of different color. Potential use of CPD-DHP photoswitch in memory devices requires a very slow thermal return in the dark in the absence of any side reaction. Herein, thermal return of CPDs to DHPs, and an unwanted sigmatropic shift in DHP is studied through density functional theory calculations at (U)B3LYP/6-31+G(d). The thermal return occurs through symmetry forbidden conrotatory electrocyclic reaction. Dimethyl amino CPD-DHP photoswitch pair has the highest activation barrier for electrocyclization and sigmatropic shifts. The lowest activation barrier for symmetry forbidden electrocyclization is observed for GeBr₃ functionalized CPD. An unprecedented decomposition pathway involving elimination of the internal substituents is predicted for Cl, Br and SMe functionalized DHPs. This study shows great promise in understanding the Woodward Hoffmann forbidden processes and, in reducing the synthetic efforts toward robust photochromes for memory applications.     

Fungal metabolites as anti-diabetic agents: emphasis on PTP1B inhibitors

Phytochemistry Reviews - In the last decade the prevalence of diabetes has escalated globally and it is estimated that the number of diabetic people will increase to 642 million by 2040. Although...     

Structural and Functional Insights into the Pilotin-Secretin Complex of the Type II Secretion System

Gram-negative bacteria secrete virulence factors and assemble fibre structures on their cell surface using specialized secretion systems. Three of these, T2SS, T3SS and T4PS, are characterized by large outer membrane channels formed by proteins called secretins. Usually, a cognate lipoprotein pilot is essential for the assembly of the secretin in the outer membrane. The structures of the pilotins of the T3SS and T4PS have been described. However in the T2SS, the molecular mechanism of this process is poorly understood and its structural basis is unknown. Here we report the crystal structure of the pilotin of the T2SS that comprises an arrangement of four α-helices profoundly different from previously solved pilotins from the T3SS and T4P and known four α-helix bundles. The architecture can be described as the insertion of one α-helical hairpin into a second open α-helical hairpin with bent final helix. NMR, CD and fluorescence spectroscopy show that the pilotin binds tightly to 18 residues close to the C-terminus of the secretin. These residues, unstructured before binding to the pilotin, become helical on binding. Data collected from crystals of the complex suggests how the secretin peptide binds to the pilotin and further experiments confirm the importance of these C-terminal residues in vivo.     

Isolation of arsenite-oxidizing bacteria from industrial effluents and their potential use in wastewater treatment

The present study is aimed at assessing the ability of Klebsiella pneumoniae and Klebsiella variicola to oxidize trivalent arsenic into its pentavalent form. K. pneumoniae could tolerate As(III) (26.6 mM) and K. variicola could tolerate As(III) (24 mM). K. pneumoniae was able to resist Cd²⁺ and Hg²⁺ (1.3 mM), Cr⁶⁺ and Cu²⁺ (6.6 mM) and Ni²⁺ (5.3 mM). K. variicola resisted Cd²⁺ (2.6 mM), Hg²⁺ (4 mM), Cr⁶⁺ (6.6 mM), Cu²⁺ (9.3 mM) and Ni²⁺ (5.3 mM). The optimum temperature and pH for K. pneumoniae and K. variicola were 7 and 30°C, respectively. K. pneumoniae could oxidize 36% As(III), 64% and 87% from the medium after 24, 48 and 72 h, respectively. Likewise K. variicola was also able to oxidize 33% As(III) after 24 h, 59% after 48 h and 83% after 72 h from the medium. The presence of an induced protein having molecular weight around 14 kDa in the presence of arsenic points out a possible role of this protein in arsenite oxidation. The bacterial isolates can be employed to bioremediate As-containing wastes.     

Photoacoustic imaging of the human placental vasculature

Minimally invasive fetal interventions require accurate imaging from inside the uterine cavity. Twin‐to‐twin transfusion syndrome (TTTS), a condition considered in this study, occurs from abnormal vascular anastomoses in the placenta that allow blood to flow unevenly between the fetuses. Currently, TTTS is treated fetoscopically by identifying the anastomosing vessels, and then performing laser photocoagulation. However, white light fetoscopy provides limited visibility of placental vasculature, which can lead to missed anastomoses or incomplete photocoagulation. Photoacoustic (PA) imaging is an alternative imaging method that provides contrast for hemoglobin, and in this study, two PA systems were used to visualize chorionic (fetal) superficial and subsurface vasculature in human placentas. The first system comprised an optical parametric oscillator for PA excitation and a 2D Fabry‐Pérot cavity ultrasound sensor; the second, light emitting diode arrays and a 1D clinical linear‐array ultrasound imaging probe. Volumetric photoacoustic images were acquired from ex vivo normal term and TTTS‐treated placentas. It was shown that superficial and subsurface branching blood vessels could be visualized to depths of approximately 7 mm, and that ablated tissue yielded negative image contrast. This study demonstrated the strong potential of PA imaging to guide minimally invasive fetal therapies.      

Characterization of two platelet aggregation inhibitor-like polypeptides from viper venom

Two polypeptides, eristocophins I and II, have been characterized from leaf-nosed viper (Eristocophis macmahoni) venom. They contain 10 half-Cys residues of a total of 61/62 residues, have 72% residue identity, and exhibit similarities to platelet aggregation inhibitors and segments of adhesive proteins. Eristocophin I contains the sequence Arg-Gly-Asp, known to inhibit fibrinogen interaction with the platelet receptor. Eristocophin II has Met instead of Arg in this sequence, and an adjacent Trp-Asn-Asp segment. The latter is also typical of adhesive proteins, thus linking two potentially functional segments in one molecule. Exchanges are maximal in these segments, suggesting that the polypeptides exhibit functional divergence with isoform differences in important regions.     

Graphene-Based Plasmonic Waveguides: a Mini Review

Plasmonics - Graphene plasmonics is one of the most explored fields since the successful experimental discovery of the graphene due to its unprecedented properties. The dynamical modulation and...