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Lysis Protein
Published in Paul Pumpens, Single-Stranded RNA Phages, 2020
In a large review on lysis mechanisms and regulation, the presence of a hydrophobic transmembrane helical domain within the protein was proclaimed as the most typical feature of so-called holins, a class of proteins that may create a lesion in the cytoplasmic membrane through which the murein hydrolase passes to gain access to the murein layer (Young 1992). The available evidence suggested that the holins oligomerize to form nonspecific holes, and that this hole-forming step was the regulated step in the phage-induced lysis, while the correct scheduling of the lysis event is as much an essential feature of the holin function as is the hole formation itself. However, with the lysis strategy used by the phage MS2, as well as by the single-stranded DNA phage φX174, no murein hydrolase activity was synthesized. Instead, there was a single species of small membrane protein, unlike the holins in primary structure, which caused disruption of the cell envelope by activation of cellular autolysins. The presence of the hydrophobic transmembrane helix was defined as obligatory also for the RNA phage lysis proteins (Young 1992).
Molecular regulation of adhesion and biofilm formation in high and low biofilm producers of Bacillus licheniformis using RNA-Seq
Published in Biofouling, 2019
Faizan Ahmed Sadiq, Steve Flint, Hafiz Arbab Sakandar, GuoQing He
Several genes related to stress response, heat shock, cold shock, oxidative stress, and osmotic stress were found to be upregulated in the biofilm state of both strains. It is evident that more genes related to stress were involved in the high biofilm forming strain compared to the low biofilm forming strain. Out of the 20 stress related genes, expressed in the biofilm state of the high biofilm former, given in Table 3, only 10 genes were expressed in the low biofilm former (Table 4). A gene (BLi0432) coding for holin was more expressed (>10 fold) in the biofilm state of both strains compared to the planktonic state. Apart from holin, two genes coding for holin-like proteins CidA and holin-like CidB/LrgB proteins (family autolysis modulator) were also found to be overexpressed in the biofilm state of both strains. One gene encoding a quorum sensing quenching molecule (N-acyl homoserine lactone hydrolase) was also found to be more expressed in the planktonic form of high and low biofilm formers. Tables 3 and 4 show the different genes involved in stress and autolysis in high and low biofilm producers, respectively.
Bacteriophage endolysins as a potential weapon to combat Clostridioides difficile infection
Published in Gut Microbes, 2020
Shakhinur Islam Mondal, Lorraine A. Draper, R Paul Ross, Colin Hill
Bacteriophages or phages are viruses that infect and kill bacteria. Bacteriophages can adopt either of two life cycles, lytic and lysogenic. Both virulent and temperate phages may enter the lytic cycle, whereas only temperate phages utilize the lysogenic cycle.33 In most cases, the lytic cycle concludes with cell lysis that leads to cell death (Figure 1a). In single stranded DNA/RNA phages, the genome encodes a lysis effector which inhibits peptidoglycan (PG) biosynthesis from within the bacterium. On the other hand, double stranded DNA (dsDNA) phages utilize phage-encoded muralytic enzymes called endolysins (or lysins) that lead to cell envelope disruption at the final stage of phage reproduction. There are three different lysis mechanisms in dsDNA phages. The most studied and best understood mechanism is canonical lysis, where endolysins require the help of a second phage-encoded protein called a holin to act on the PG layer.34 Holin proteins accumulate and oligomerize in the cytoplasmic membrane (CM) in a time-controlled manner, and trigger depolarization and the formation of holes in the CM. This allows diffusion of endolysin to the membrane, facilitating the destruction of the PG layer (Figure 1b). The second mechanism requires a special class of holins, called pinholins, which form small, heptameric channels that help to depolarize the membrane. In the third mechanism, the lysis of the outer membrane of Gram-negative hosts is facilitated by spanin proteins.35 Spanins form a complex with outer membrane (OM) lipoprotein (o-spanin) and an integral cytoplasmic membrane protein (i-spanin) and disrupt the OM by enzymatic degradation, pore formation and inner membrane-outer membrane fusion.36–38