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PubMed2004

The bifunctional peptidoglycan lysin of Streptococcus agalactiae bacteriophage B30.

A group B streptococcal (GBS) bacteriophage lysin gene was cloned and expressed in Escherichia coli. The purified recombinant enzyme, calculated to have a molecular mass of 49 677 Da, lysed GBS cells. The susceptibility of GBS cells to lysis by the enzyme depended upon the growth stage at which they were harvested, with early exponential phase cells most sensitive. Calcium ions enhanced the activity of the enzyme. The enzyme also lysed other beta-haemolytic streptococci, including groups A, C, E and G streptococci, but not common oral streptococci, including Streptococcus mutans. The generation of both reducing activity and N-terminal alanine residues during lysis indicated that the lysin is a bifunctional enzyme, possessing both glycosidase and endopeptidase activities. This is consistent with the presence of two conserved sequence domains, an Acm (acetylmuramidase) domain associated with lysozyme activity, and a CHAP (cysteine, histidine-dependent amidohydrolases/peptidases) domain associated with endopeptidase activity. Site-directed mutagenesis of conserved cysteine and histidine residues in the CHAP domain and conserved aspartate and glutamate residues in the Acm domain confirmed their importance for lysozyme and endopeptidase activity respectively.

Bacteriolysis↗
PubMed2005

Acd, a peptidoglycan hydrolase of Clostridium difficile with N-acetylglucosaminidase activity.

A gene encoding a putative peptidoglycan hydrolase was identified by sequence similarity searching in the Clostridium difficile 630 genome sequence, and the corresponding protein, named Acd (autolysin of C. difficile) was expressed in Escherichia coli. The deduced amino acid sequence of Acd shows a modular structure with two main domains: an N-terminal domain exhibiting repeated sequences and a C-terminal catalytic domain. The C-terminal domain exhibits sequence similarity with the glucosaminidase domains of Staphylococcus aureus Atl and Bacillus subtilis LytD autolysins. Purified recombinant Acd produced in E. coli was confirmed to be a cell-wall hydrolase with lytic activity on the peptidoglycan of several Gram-positive bacteria, including C. difficile. The hydrolytic specificity of Acd was studied by RP-HPLC analysis and MALDI-TOF MS using B. subtilis cell-wall extracts. Muropeptides generated by Acd hydrolysis demonstrated that Acd hydrolyses peptidoglycan bonds between N-acetylglucosamine and N-acetylmuramic acid, confirming that Acd is an N-acetylglucosaminidase. The transcription of the acd gene increased during vegetative cellular growth of C. difficile 630. The sequence of the acd gene appears highly conserved in C. difficile strains. Regarding deduced amino acid sequences, the C-terminal domain with enzymic function appears to be the most conserved of the two main domains. Acd is the first known autolysin involved in peptidoglycan hydrolysis of C. difficile.

Acetylglucosaminidase↗
PubMed2005

Functional analysis of the lysis genes of Staphylococcus aureus phage P68 in Escherichia coli.

Double-stranded DNA phages of both Gram-positive and Gram-negative bacteria typically use a holin-endolysin system to achieve lysis of their host. In this study, the lysis genes of Staphylococcus aureus phage P68 were characterized. P68 gene lys16 was shown to encode a cell-wall-degrading enzyme, which causes cell lysis when externally added to clinical isolates of S. aureus. Another gene, hol15, was identified embedded in the -1 reading frame at the 3' end of lys16. The deduced Hol15 protein has three putative transmembrane domains, and thus resembles class I holins. An additional candidate holin gene, hol12, was found downstream of the endolysin gene lys16 based on two predicted transmembrane domains of the encoded protein, which is a typical trait of class II holins. The synthesis of either Hol12 or Hol15 resulted in growth retardation of Escherichia coli, and both hol15 and hol12 were able to complement a phage lambda Sam mutation. The hol15 gene has a dual start motif beginning with the codons Met1-Lys2-Met3.... Evidence is presented that the hol15 gene encodes a lysis inhibitor (anti-holin) and a lysis effector (actual holin). As depolarization of the membrane converted the anti-holin to a functional holin, these studies suggested that hol15 functions as a typical dual start motif class I holin. The unusual arrangement of the P68 lysis genes is discussed.

Amino Acid Sequence↗
PubMed2006

Interaction of the transmembrane domain of lysis protein E from bacteriophage phiX174 with bacterial translocase MraY and peptidyl-prolyl isomerase SlyD.

The molecular target for the bacteriolytic E protein from bacteriophage X174, responsible for host cell lysis, is known to be the enzyme phospho-MurNAc-pentapeptide translocase (MraY), an integral membrane protein involved in bacterial cell wall peptidoglycan biosynthesis, with an essential role being played by peptidyl-prolyl isomerase SlyD. A synthetic 37 aa peptide E(pep), containing the N-terminal transmembrane alpha-helix of E, was found to be bacteriolytic against Bacillus licheniformis, and inhibited membrane-bound MraY. The solution conformation of E(pep) was found by circular dichroism (CD) spectroscopy to be 100 % alpha-helical. No change in the CD spectrum was observed upon addition of purified Escherichia coli SlyD, implying that SlyD does not catalyse prolyl isomerization upon E. However, E(pep) was found to be a potent inhibitor of SlyD-catalysed peptidyl-prolyl isomerization (IC(50) 0.15 microM), implying a strong interaction between E and SlyD. E(pep) was found to inhibit E. coli MraY activity when assayed in membranes (IC(50) 0.8 microM); however, no inhibition of solubilized MraY was observed, unlike nucleoside natural product inhibitor tunicamycin. These results imply that the interaction of E with MraY is not at the MraY active site, and suggest that a protein-protein interaction is formed between E and MraY at a site within the transmembrane region.

Anti-Bacterial Agents↗
PubMed1993

A switch in translation mediated by an antisense RNA.

Antisense RNAs regulate expression of target genes in a variety of ways--transcription termination, translation initiation, and mRNA stability. We describe a case in which the target gene encodes two polypeptides, and antisense RNA causes a switch in its translation by selectively inhibiting synthesis of one of the polypeptides. Bacteriophage P22 is a temperate Salmonella phage; in the prophage state it expresses only a handful of its genes. One of these genes, sieB, aborts the lytic development of some phages. P22 itself is insensitive to the lethal effect of SieB because it harbors a determinant called esc. We show that the sieB gene encodes two polypeptides--SieB, which is the exclusion protein, and Esc, which is a truncated version of SieB that inhibits its action. Superinfecting P22 synthesizes an antisense RNA, sas, that inhibits synthesis of SieB but allows continued synthesis of Esc, thus allowing P22 to bypass SieB-mediated exclusion. This translational switch induced by sas RNA is essential to vegetatively developing P22; a mutation that prevents this switch causes P22 to commit SieB-mediated suicide. Finally, we show that P22's Esc allows it to circumvent the SieB-mediated exclusion system of bacteriophage lambda.

Bacteriolysis↗
PubMed1975

Studies on gonococcal infection. I. Electron microscopic studies on phagocytosis of Neisseria gonorrhoeae by macrophages.

Macrophages from mice were infected with Neisseria gonorrhoeae type 1 cells, and their ultrastructure was studied by electron microscopy. The macrophages showed various stages of engulfment and digestion of gonococci 2 hr after infection. Infected macrophages seemed to develop pseudopodia for phagocytosis, and could engulf more than 30 gonococcal cells. Some engulfed bacteria appeared morphologically intact, while others appeared lysed and some structures resembling the L form of N. gonorrhoeae were also seen. These observations suggest that gonococcal cells may be able to survive intracellularly with normal or altered forms of morphology, and that macrophages containing these bacteria may disseminate gonococcal infection in man.

Animals↗
PubMed1976

Isolation of a small rod with lytic activity against Vibrio parahaemolyticus from fresh sea water.

A small rod, capable of formine crater-like plaques on lawns of Vibrio parahaemolyticus, was isolated from a marine environment. The isolate was a gram-negative straight rod with round ends and was small in size, equal to that of halophilic Bdellovibrio strain 5501. The isolate appeared to have close taxonomic relationships to Cytophaga, since this bacterium moved slowly in a gliding manner on a solid agar surface, hydrolyzed agar and starch, contained yellow pigment and was halophilic. The isolate was able to grow not only under host-dependent but also under host-independent conditions when low nutrient media were used for cultivation, and its bacteriolytic mode was different from that of Bdellovibrio, an endoparasite. The isolate was halophilic and required Mg++ and Ca++ in addition to 3% saline for growth. The isolate showed a broad host rnage when tested for plaque-forming activity on gram-negative bacteria but not on the gram-positive bacteria tested so far.

Bacteria↗
PubMed1980

Morphological changes during conversion of Clostridium saccharoperbutylacetonicum to protoplasts by sucrose-induced autolysis.

When exponentially growing cells of Clostridium saccharoperbutylacetonicum (ATCC 13564) were exposed to hypertonic concentrations of sucrose (0.3--0.5 M), rapid degradation of the cell wall occurred (sucrose-induced autolysis). The morphological changes from the original rod-shaped cells to protoplasts during the sucrose-induced autolysis were investigated by phase contrast and electron microscopy. When the cells were autolysed in the sucrose solution (0.35 M), each cell began to swell at the middle or at one pole and then formed a small bulb at the swollen part. The bulk consisted of the cytoplasm which was enveloped by the plasma membrane and extruded from the small gap produced by the degradation of the cell wall. The bulb gradually enlarged as lysis progressed, and finally became a protoplast which had no cell wall. The large pre-division cell frequently formed the bulb at the middle (septal site), while the small post-division cell formed the bulb at the pole.

Autolysis↗