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  • 1
    Unknown
    Boston, MA : Springer
    Keywords: Food science ; Microbiology
    ISBN: 9780387234137
    Language: English
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  • 2
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Listeria monocytogenes phage endolysins Ply118 and Ply500 share a unique enzymatic activity and specifically hydrolyse Listeria cells at the completion of virus multiplication in order to release progeny phage. With the aim of determining the molecular basis for the lytic specificity of these enzymes, we have elucidated their domain structure and examined the function of their unrelated and unique C-terminal cell wall binding domains (CBDs). Analysis of deletion mutants showed that both domains are needed for lytic activity. Fusions of CBDs with green fluorescent protein (GFP) demonstrated that the C-terminal 140 amino acids of Ply500 and the C-terminal 182 residues of Ply118 are necessary and sufficient to direct the murein hydrolases to the bacterial cell wall. CBD500 was able to target GFP to the surface of Listeria cells belonging to serovar groups 4, 5 and 6, resulting in an even staining of the entire cell surface. In contrast, the CBD118 hybrid bound to a ligand predominantly present at septal regions and cell poles, but only on cells of serovars 1/2, 3 and 7. Non-covalent binding to surface carbohydrate ligands occurred in a rapid, saturation-dependent manner. We measured 4 × 104 and 8 × 104 binding sites for CBD118 and CBD500 respectively. Surface plasmon resonance analysis revealed unexpected high molecular affinity constants for the CBD–ligand interactions, corresponding to nanomolar affinities. In conclusion, we show that the CBDs are responsible for targeting the phage endolysins to their substrates and function to confer recognition specificity on the proteins. As the CBD sequences contain no repeats and lack all known sequence motifs for anchoring of proteins to the bacterial cell, we conclude that they use unique structural motifs for specific association with the surface of Gram-positive bacteria.
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  • 3
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The bacteriophage lysis cassette, which comprises a lysin and a holin gene, was analyzed in 18 Lactococcus lactis phages. A muramidase motif was found in the lysins of c2-like phages, while an amidase motif was observed in the lysins of 936-like phages. Both amidase and muramidase types were detected among the P335 phages. The P335 lysins were separated into three groups based on amino acid sequence identity. A class I holin was recognized in 936-like and c2-like phages, whereas P335-like phages possess class II holins. The P335 holins were further divided into four groups based on sequence identity. Only the holins of 936-like phages contained putative dual-start motifs. The unusual lysis cassette of the highly virulent P335-like phage ul36 contains a unique holin (orf74B) upstream of a lysin which is present in several other P335-like phages. Using the λΔSthf system, we demonstrated that gpORF74B induces cell lysis at the same time as λΔSthf::S105, the effector of λ lysis. Transcriptional analysis of ul36 lysis cassette showed that first transcripts are detected 35 min after infection of L. lactis cells. The lysis clock of phage ul36 appears to be controlled by the late expression of the holin and lysin genes.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 184 (2000), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Holins are small hydrophobic proteins causing non-specific membrane lesions at the end of bacteriophage multiplication, to promote access of the murein hydrolase to their substrate. We have established a λΔS genetic system, which enables functional expression of holins from various phages in an isogenic phage λ background, and allows qualitative evaluation of their ability to support lysis of Escherichia coli cells. Synthesis of Holins is under control of native λ transcription and translation initiation signals, and the temperature-sensitive CIts857 repressor. A number of different holins were tested in this study. The opposing action of phage λ S105 and S107 holin variants in lysis timing could be confirmed, whereas we found evidence for a functionally non-homologous dual translational start motif in the Listeria phage Hol500 holin, i.e., the Hol500-96 polypeptide starting at Met-1 revealed a more distinct lytic activity as compared to the shorter product Hol500-93. The largest holin known, HolTW from a Staphylococcus aureus phage, revealed an early lysis phenotype in the λΔSthf background, which conferred a plaque forming defect due to premature lysis. Mutant analysis revealed that an altered C-terminus and/or a V52L substitution were sufficient to delay lysis and enable plaque formation. These results suggest that the extensively charged HolTW C-terminus may be important in regulation of lysis timing. The gene 17.5 product of E. coli phage T7 was found to support sudden, saltatory cell lysis in the λΔSthf background, which clearly confirms its holin character. In conclusion, λΔSthf offers a useful genetic tool for studying the structure–function relationship of the extremely heterogeneous group of holin protein orthologs.
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  • 5
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The lysis genes of the virulent Staphylococcus aureus bacteriophage Twort were cloned and their nucleotide sequences determined. The endolysin gene plyTW encodes a 53.3-kDa protein, whose catalytic site is located in the amino-terminal domain. An enzymatically active fragment (N-terminal 271 amino acids) was overexpressed in Escherichia coli and partially purified. The enzyme rapidly cleaves staphylococcal peptidoglycan, and was shown to act as N-acetylmuramoyl-l-alanine amidase (EC 3.5.1.28). Significant sequence homology to the specific cell wall targeting domain of lysostaphin was observed in a 101-amino acid C-terminal overlap. However, we found that the large C-terminal portion (63%, 295 aa) of PlyTW is not required for staphylolytic activity. Located upstream of and overlapping plyTW by 35 bp in a different reading frame (+1), we identified holTW, which starts with a single TTG triplet. The gene specifies a 185-amino acid (20.5 kDa) holin protein, which features two potential hydrophobic, antiparallel transmembrane domains, and a highly charged, acidic C-terminus. HolTW is the largest class II holin described to date. It can substitute for the defective allele in phage λS amber mutants, both in trans from an expression plasmid, and from within gt11::holTW. The proposed function is the formation of unspecific membrane lesions to promote access of the endolysin to the bacterial peptidoglycan.
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  • 6
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Listeria monocytogenes bacteriophages A118, A500 and A511 are members of three distinct phage groups with characteristic host ranges. Their endolysin (ply) genes were colonies and expressed in Escherichia coli as demonstrated by the conferred lytic phenotype when colonies of recombinant cells were overlaid with a lawn of Listeria ceils. The nucleotide sequences of the cloned DNA fragments were determined and the individual enzymes (PLY118, 30.8 kDa; PLY500, 33.4 kDa; PLY511, 36.5 kDa) were shown to have varying degrees of homology within their N-terminal or C-terminal domains. Transcriptional analysis revealed them to be‘late’genes with transcription beginning 15–20 min post-infection. The enzymes were over-expressed and partially purified and their individual specificities examined. When applied exogenously, the lysins induced rapid lysis of Listeria strains from all species but generally did not affect other bacteria. Using hydrolysis of purified listerial cell walls, PLY511 was characterized as an N-acetylmuramoyl-L-alanine amidase (EC 3.5.1.28) and shows homology in its N-terminal domain to other enzymes of this type. In contrast, PLY118 and PLY500 were shown to represent a new class of cell wall lytic enzymes which cleave between the L-alanine and D-glutamate residues of listerial peptidoglycan; these were designated as L-alanoyl-D-glutamate peptidases. These two enzymes share homology in the N-terminal domain which we propose determines hydrolytic specificity. Highly conserved holin (hol) gene sequences are present upstream of ply118 and ply500. They encode proteins of structural similarity to the product of phage lambda gene S, and are predicted to be membrane proteins which form pores to allow access of the lysins to their peptidoglycan substrates. This arrangement of conserved holin genes with downstream lysin genes among the siphoviral lysis cassettes explains why the cytoplasmic endolysins alone are not lethal, since they require a specific transport function across the cell membrane.
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  • 7
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A118 is a temperate phage isolated from Listeria monocytogenes. In this study, we report the entire nucleotide sequence and structural analysis of its 40 834 bp DNA. Electron microscopic and enzymatic analyses revealed that the A118 genome is a linear, circularly permuted, terminally redundant collection of double-stranded DNA molecules. No evidence for cohesive ends or for a terminase recognition (pac) site could be obtained, suggesting that A118 viral DNA is packaged via a headful mechanism. Partial denaturation mapping of DNA cross-linked to the tail shaft indicated that DNA packaging proceeds from left to right with respect to the arbitrary genomic map and the direction of genes necessary for lytic development. Seventy-two open reading frames (ORFs) were identified on the A118 genome, which are apparently organized in a life cycle-specific manner into at least three major transcriptional units. N-terminal amino acid sequencing, bioinformatic analyses and functional characterizations enabled the assignment of possible functions to 26 ORFs, which included DNA packaging proteins, morphopoetic proteins, lysis components, lysogeny control-associated functions and proteins necessary for DNA recombination, modification and replication. Comparative analysis of the A118 genome structure with other bacteriophages revealed local, but sometimes extensive, similarities to a number of phages spanning a broader phylogenetic range of various low G+C host bacteria, which implies relatively recent exchange of genes or genetic modules. We have also identified the A118 attachment site attP and the corresponding attB in Listeria monocytogenes, and show that site-specific integration of the A118 prophage by the A118 integrase occurs into a host gene homologous to comK of Bacillus subtilis, an autoregulatory gene specifying the major competence transcription factor.
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  • 8
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: PSA is a temperate phage isolated from Listeria monocytogenes strain Scott A. We report its complete nucleotide sequence, which consists of a linear 37 618 bp DNA featuring invariable, 3′-protruding single stranded (cohesive) ends of 10 nucleotides. The physical characteristics were confirmed by partial denaturation mapping and electron microscopy of DNA molecules. Fifty-seven open reading frames were identified on the PSA genome, which are apparently organized into three major transcriptional units, in a life cycle-specific order. Functional assignments could be made to 33 gene products, including structural proteins, lysis components, DNA packaging proteins, lysogeny control functions and replication proteins. Bioinformatics demonstrated relatedness of PSA to phages infecting lactic acid bacteria and other low G + C Gram-positives, but revealed only few similarities to Listeria phage A118. Virion proteins were analysed by amino acid sequencing and mass spectrometry, which enabled identification of major capsid and tail proteins, a tape measure and a putative portal. These analyses also revealed an unusual form of translational frameshifting, which occurs during decoding of the mRNAs specifying the two major structural proteins. Frameshifting yields different length forms of Cps (gp5) and Tsh (gp10), featuring identical N-termini but different C-termini. Matrix-assisted laser-desorption ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS) of tryptic peptide fragments was used to identify the modified C-termini of the longer protein species, by demonstration of specific sequences resulting from + 1 programmed translational frameshifting. A slippery sequence with overlapping proline codons near the 3′ ends of both genes apparently redirects the ribosomes and initiates the recoding event. Two different cis-acting factors, a shifty stop and a pseudoknot, presumably stimulate frameshifting efficiency. PSA represents the first case of + 1 frameshifting among dsDNA phages, and appears to be the first example of a virus utilizing a 3′ pseudoknot to stimulate such an event.
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  • 9
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We have dissected the functional properties of the holin encoded by Listeria monocytogenes bacteriophage A118. Native hol118 was cloned into λΔSthf, devoid of the S holin, and tested in an E. coli background. Surprisingly, it caused very late cell lysis, beginning at 80 min after induction. Immunological analyses demonstrated that Hol118 appears in the cytoplasmic membrane shortly after infection. The hol118 gene features a dual start motif similar to λ S. Therefore, different N-terminally modified Hol118 variants were tested. However, in contrast to λ S, inactivation of AUG-1 or AUG-2 showed no significant influence on lysis timing. In addition, Hol118-mediated lysis could not be triggered by energy poisons, indicating a functional regulation different from that of S. Toeprinting assays on hol118 mRNA revealed an unexpected translational start codon (AUG-3) at nucleotide position 40. We demonstrated by in vitro and in vivo approaches that the predicted Hol118(83) product is actually produced together with the full-length polypeptide. However, although the truncated holin lacking its first transmembrane domain appeared in the cytoplasmic membrane, it was shown to be functionally deficient and unable to support λ R-mediated lysis. In contrast, specific mutations introduced to abolish translation initiation at AUG-3 drastically accelerated lysis, pointing to an inhibitor function of Hol118(83). This hypothesis was supported by the observation that hol118(83) inhibited holin function when expressed in trans. A deviation from the λ S paradigm is proposed, which represents a new model of holin functional regulation: the intragenic, in frame translated Hol118(83) product, which is devoid of its first transmembrane domain, acts as a functional inhibitor and constitutes a key part of the lysis clock of A118. Presence of the dominant inhibitor function also explains the long latent period of A118, where the onset of lysis takes about 70 min, more than twice the time needed by λ.
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  • 10
    ISSN: 0173-0835
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: A simple procedure for the elimination of lateral sample as well as band spreading in precast, ready-made immobilized pH gradient gels is described. Round or rectangular holes are punched in the dry polyacrylamide gels prior to rehydration. The generated wells proved suitable for application of samples containing surfactants such as Nonidet P-40 or 3-[(3-cholamidopropyl) dimethylammonio]-1-propane-sulfonate (CHAPS). Lateral band spreading and precipitation of samples containing up to 9.5 M urea could be completely eliminated by this method.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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