1.E.30 The Vibrio Holin (Vibrio Holin) Family
Members of the Vibrio Holin family are short (45 - 50 aas) with a single N-terminal TMS. One of them is part of the lysis system of the lipid-containing double-stranded DNA bacteriophage PM2 infecting Gram-negative marine Pseudoalteromonas species (Krupovic et al. 2007). Phage PM2 uses a novel system to disrupt the infected cell. The Gp-K protein is needed for the permeabilization of the cytoplasmic membrane and appears to play the role of a typical holin. It has 53 aas and 1 transmembrane domain (TMD)]. Unlike other bacteriophages studied, PM2 relies on lytic factors of a cellular origin for digestion of the peptidoglycan. Another protein, Gp-l (51 aa, no TMDs), is needed for disruption of the outer membrane, which is highly rigidified by the divalent cations abundant in the marine environment. Gp-l has no precedent in other phage lytic systems studied so far, but is present in genomes of other bacterial viruses suggesting that the same system might be used by other phages and is not unique to PM2.