MorphoCatcher: a multiple-alignment based web tool for target selection and designing taxon-specific primers in the loop-mediated isothermal amplification method

Background Advantages of loop-mediated isothermal amplification in molecular diagnostics allow to consider the method as a promising technology of nucleic acid detection in agriculture and medicine. A bioinformatics tool that provides rapid screening and selection of target nucleotide sequences with subsequent taxon-specific primer design toward polymorphic orthologous genes, not only unique or conserved common regions of genome, would contribute to the development of more specific and sensitive diagnostic assays. However, considering features of the original software for primer selection, also known as the PrimerExplorer (Eiken Chemical Co. LTD, Tokyo, Japan), the taxon-specific primer design using multiple sequence alignments of orthologs or even viral genomes with conservative architecture is still complicated. Findings Here, MorphoCatcher is introduced as a fast and simple web plugin for PrimerExplorer with a clear interface. It enables an execution of multiple-alignment based search of taxon-specific mutations, visual screening and selection of target sequences, and easy-to-start specific primer design using the PrimerExplorer software. The combination of MorphoCatcher and PrimerExplorer allows to perform processing of the multiple alignments of orthologs for informative sliding-window plot analysis, which is used to identify the sequence regions with a high density of taxon-specific mutations and cover them by the primer ends for better specificity of amplification. Conclusions We hope that this new bioinformatics tool developed for target selection and taxon-specific primer design, called the MorphoCatcher, will gain more popularity of the loop-mediated isothermal amplification method for molecular diagnostics community. MorphoCatcher is a simple web plugin tool for the PrimerExplorer software which is freely available only for non-commercial and academic users at http://morphocatcher.ru

Crystal structure and location of gp131 in the bacteriophage phiKZ virion

Pseudomonas phage phi KZ and its two close relatives phi PA3 and 201 phi 2-1 are very large bacteriophages that form a separate branch in phage classification because their genomes are very different from the rest of GenBank sequence data. The contractile tail of phi KZ is built from at least 32 different proteins, but a definitive structural function is assigned to only one of them-the tail sheath protein. Here, we report the crystal structure of the C-terminal domain of another phiKZ tail protein, gene product 131 (gp131C). We show that gp131 is located at the periphery of the baseplate and possibly associates with fibers that emanate from the baseplate. Gp131C is a seven-bladed beta-propeller that has a shape of a skewed toroid. A small but highly conserved and negatively charged patch on the surface of gp131C might be important for substrate binding or for interaction with a different tail protein. (C) 2012 Elsevier Inc. All rights reserved

Abstract P-46: Structure of A. Baumannii Phage Tapaz, Revealed with Cryo-Electron Microscopy

Background: Acinetobacter baumannii is an opportunistic pathogen and one of the six most important multidrug resistant microorganisms in hospitals worldwide. Some of its strains are resistant to most of the antibiotics, A. baumannii is included into the Priority 1 part of Global Priority List of Antibiotic-resistant Bacteria. Phage therapy is considered to be an alternative strategy to antibiotic treatments. Methods: A. baumannii strain NIPH601 cells were grown till OD6000.4 and infected with the phage at MOI 10:1. After complete lysis took place cell debris was spined down and phage particles were precipitated with the PEG6000 (final concentration 10% PEG 6000, 0.5 NaCl). Virus particles were collected by centrifugation, resuspended at SM buffer and applied on CsCl step gradient. Gradient was spinned down for 2 hours at 40000g and the fraction containing phage particles was collected and dialyzed against SM buffer. Purified phage particles were applied to Quantifoil 1.2/1.3 grids and plunge-froze in Vitrobot Mark IV (TFS) Micrographs were collected in HKU, Shenzhen campus with Titan Krios cryoelectron microscope (TFS), equipped with Gatan K3 direct electron detector. The micrographs were acquired with 1.06 Å pixel size and 1.5 um average defocus value in counting mode with 50 frames and 1.2 e/Å2/frame dose rate. All image processing was performed with Relion3.0 software, except for the particle picking step performed with cryolo. Results: Lytic A. baumannii phage TaPaz belongs to the family Myoviridae. BLAST search over NCBI “nr” (non-redundant) database revealed close homology with previously published sequences of Acinetobacter phage vB_AbaM_B9 and Acinetobacter phage BS46. However, no structural information about any homologous proteins was found among the PDB structures. The cryo-EM map was reconstructed with single particle analysis independently for the capsid, tail and baseplate regions. The capsid was reconstructed at 3.9 Å resolution with I3 symmetry applied (Fig. 1A). The baseplate region of the phage was reconstructed at 3.5 Å resolution with C3 symmetry (Fig. 1B). The tail region was reconstructed at 2.6 Å resolution with helical symmetry (Rise 36.4 Å, Twist 25.7 deg). Initial atomic model for the tail region was built from sequence with Deeptracer and was further refined in coot (Fig. 1C). Conclusion: We successfully obtained the near-atomic resolution structural map of phage TaPaz. The data obtained contribute to enhancing knowledge of structural diversity of bacterial viruses infecting A. baumannii

Structure of an Acinetobacter Broad-Range Prophage Endolysin Reveals a C-Terminal α-Helix with the Proposed Role in Activity against Live Bacterial Cells

Proteins that include enzymatic domain degrading the bacterial cell wall and a domain providing transport through the bacterial outer membrane are considered as prospective compounds to combat pathogenic Gram-negative bacteria. This paper presents an isolation and study of an enzyme of this class naturally encoded in the prophage region of Acinetobacter baumannii AB 5075 genome. Recombinant protein expressed in E. coli exhibits an antimicrobial activity with respect to live cultures of Gram-negative bacteria reducing the population of viable bacteria by 1.5–2 log colony forming units (CFU)/mL. However the protein becomes rapidly inactivated and enables the bacteria to restore the population. AcLys structure determined by X-ray crystallography reveals a predominantly α—helical fold similar to bacteriophage P22 lysozyme. The С-terminal part of AcLys polypeptide chains forms an α—helix enriched by Lys and Arg residues exposed outside of the protein globule. Presumably this type of structure of the C-terminal α—helix has evolved evolutionally enabling the endolysin to pass the inner membrane during the host lysis or, potentially, to penetrate the outer membrane of the Gram-negative bacteria

Development of qPCR Detection Assay for Potato Pathogen <i>Pectobacterium atrosepticum</i> Based on a Unique Target Sequence

The recent taxonomic diversification of bacterial genera Pectobacterium and Dickeya, which cause soft rot in plants, focuses attention on the need for improvement of existing methods for the detection and differentiation of these phytopathogens. This research presents a whole genome-based approach to the selection of marker sequences unique to particular species of Pectobacterium. The quantitative real-time PCR assay developed is selective in the context of all tested Pectobacterium atrosepticum strains and is able to detect fewer than 102 copies of target DNA per reaction. The presence of plant DNA extract did not affect the sensitivity of the assay

Enzymatic Characterization of an Endolysin Mediated by Chaperonin in Bacteriophage phi EL

Bacteriophage phi-EL is a virus that attacks the human pathogen Pseudomonas aeruginosa. One of the gene products from phi-EL is a putative endolysin. Endolysin is an enzyme produced during gene expression in the lytic cycle of the bacteriophage. Its function is to digest the peptidoglycan layer of the host cell wall, thereby releasing the newly formed virions. In order to confirm the identity of this putative endolysin, the gene product was transformed into competent E. coli cells, expressed to high levels and purified to high homogeneity using nickel affinity and size exclusion chromatography. The peptidoglycan-hydrolyzing activity of the protein was characterized using a fluorescence-based assay. Assay results demonstrated that the endolysin activity was similar to the peptidoglycan-hydrolyzing activity of Gallus gallus lysozyme , which supports the identity of the putative gene product as an endolysin. The kinetics of the reaction have been analyzed and calculated. X-ray crystallography will be utilized to determine the structure of endolysin. Structure determination of this protein will be used to study the lytic cycle of the bacteriophage phi-EL and function of the endolysin. This can lead to manipulation of bacterial lysis that can in turn provide treatments and medication for bacterial infections

Biochemical Characterization and X-ray Crystallography of a Lysozyme Encoded by Pseudomonas aeruginosa Bacteriophage SN

Bacteriophage SN is a virulent phage that selectively infects the bacterium Pseudomonas aeruginosa. It was isolated from Lake Chernoe in Russia and it is related to the PB1-like species of the Myoviridae family. The DNA genome is composed of 66,391 base pairs, has 89 predicted open reading frames, and encodes more than 20 structural proteins. One of the open reading frames of this newly discovered bacteriophage has high sequence identity to other lysozyme and chitinase genes. It is therefore assumed that this protein encoded by bacteriophage SN is utilized for digestion of the host cell wall prior to injection of the nucleic acid into the host. Determining the high-resolution structure of the protein will aid in later determination of location within the intact phage. The gene of interest has been cloned into E. coli by PCR amplification and ligation into the PET30a vector. This protein expressed to high levels and the product has been purified to homogeneity. The protein demonstrated specific enzymatic activity by lysis of Micrococcus luteus cells in suspension as purity increased. Crystals of the protein currently diffract to 3.5 Å, the data gathered from optimized crystals will be used to determine the X-ray structure of the lysozyme

Autographivirinae Bacteriophage Arno 160 Infects Pectobacterium carotovorum via Depolymerization of the Bacterial O-Polysaccharide

Phytopathogenic bacteria belonging to the Pectobacterium and Dickeya genera (soft-rot Pectobacteriaceae) are in the focus of agriculture-related microbiology because of their diversity, their substantial negative impact on the production of potatoes and vegetables, and the prospects of bacteriophage applications for disease control. Because of numerous amendments in the taxonomy of P. carotovorum, there are still a few studied sequenced strains among this species. The present work reports on the isolation and characterization of the phage infectious to the type strain of P. carotovorum. The phage Arno 160 is a lytic Podovirus representing a potential new genus of the subfamily Autographivirinae. It recognizes O-polysaccahride of the host strain and depolymerizes it in the process of infection using a rhamnosidase hydrolytic mechanism. Despite the narrow host range of this phage, it is suitable for phage control application

Related structures of neutral capsular polysaccharides of Acinetobacter baumannii isolates that carry related capsule gene clusters KL43, KL47, and KL88

<b>Highlights</b>\ud \ud - Capsular polysaccharide structures of four A. baumannii isolates were elucidated.\ud \ud - Repeating units of the capsular polysaccharides studied share a trisaccharide fragment.\ud \ud - Gene clusters for capsule biosynthesis of the strains studied are related.\ud \ud Capsular polysaccharides were recovered from four Acinetobacter baumannii isolates, and the following related structures of oligosaccharide repeating units were established by sugar analyses along with 1D and 2D¹H and ¹³C NMR spectroscopy:\ud \ud <i>NIPH 60 and LUH5544 (K43)</i>\ud \ud <i>NIPH 601 (K47)</i>\ud \ud The K locus for capsule biosynthesis in the genome sequences available for NIPH 60 and LUH5544, designated KL43, was found to be related to gene clusters KL47 in NIPH 601 and KL88 in LUH5548. The three clusters share most gene content differing in only a small portion that includes an additional glycosyltransferase genes in KL47 and KL88, as well as genes encoding distinct Wzy polymerases that were found to form the same α-d-GlcpNAc-(1 → 6)-α-d-GlcpNAc linkage in K43 and K47

The chemoenzymatic synthesis of clofarabine and related 2′-deoxyfluoroarabinosyl nucleosides: the electronic and stereochemical factors determining substrate recognition by E. coli nucleoside phosphorylases

Two approaches to the synthesis of 2-chloro-9-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)adenine (1, clofarabine) were studied. The first approach consists in the chemical synthesis of 2-deoxy-2-fluoro-α-D-arabinofuranose-1-phosphate (12a, 2FAra-1P) via three step conversion of 1,3,5-tri-O-benzoyl-2-deoxy-2-fluoro-α-D-arabinofuranose (9) into the phosphate 12a without isolation of intermediary products. Condensation of 12a with 2-chloroadenine catalyzed by the recombinant E. coli purine nucleoside phosphorylase (PNP) resulted in the formation of clofarabine in 67% yield. The reaction was also studied with a number of purine bases (2-aminoadenine and hypoxanthine), their analogues (5-aza-7-deazaguanine and 8-aza-7-deazahypoxanthine) and thymine. The results were compared with those of a similar reaction with α-D-arabinofuranose-1-phosphate (13a, Ara-1P). Differences of the reactivity of various substrates were analyzed by ab initio calculations in terms of the electronic structure (natural purines vs analogues) and stereochemical features (2FAra-1P vs Ara-1P) of the studied compounds to determine the substrate recognition by E. coli nucleoside phosphorylases. The second approach starts with the cascade one-pot enzymatic transformation of 2-deoxy-2-fluoro-D-arabinose into the phosphate 12a, followed by its condensation with 2-chloroadenine thereby affording clofarabine in ca. 48% yield in 24 h. The following recombinant E. coli enzymes catalyze the sequential conversion of 2-deoxy-2-fluoro-D-arabinose into the phosphate 12a: ribokinase (2-deoxy-2-fluoro-D-arabinofuranose-5-phosphate), phosphopentomutase (PPN; no 1,6-diphosphates of D-hexoses as co-factors required) (12a), and finally PNP. The substrate activities of D-arabinose, D-ribose and D-xylose in the similar cascade syntheses of the relevant 2-chloroadenine nucleosides were studied and compared with the activities of 2-deoxy-2-fluoro-D-arabinose. As expected, D-ribose exhibited the best substrate activity [90% yield of 2-chloroadenosine (8) in 30 min], D-arabinose reached an equilibrium at a concentration of ca. 1:1 of a starting base and the formed 2-chloro-9-(β-D-arabinofuranosyl)adenine (6) in 45 min, the formation of 2-chloro-9-(β-D-xylofuranosyl)adenine (7) proceeded very slowly attaining ca. 8% yield in 48 h