1.E.5 The PRD1 Phage P35 Holin (P35 Holin) Family
The prototype for this family is the lipid-containing PRD1 enterobacterial phage holin protein P35 (12.8 kDa) encoded by gene XXXV (orfT) (Rydman and Bamford, 2003). It is a component of a typical holin-endolysin system which functions to lyse the host bacterial cell. The autolysin is the gene XV product, P15, a soluble β1,4-N-acetylmuramidase that causes lysis following digestion of the Gram-negative bacterial cell wall. A defect in its structural gene can be corrected by expression of the lambda phage S gene encoding the lambda holin.
P35 holin has 3 TMSs with 5 positively charged residues between TMSs 1 and 2 and 4 at the C-terminus (Rydman and Bamford, 2003). It is therefore likely that the N-terminus is in the periplasm and the C-terminus is in the cytoplasm. Homologues of 109 aa, which also have 3 putative TMSs, are encoded in the genomes of Xylella fastidiosa strains (25% identity; 46% similarity; no gaps).
PRD1 infects gram-negative cells harboring a conjugative IncP plasmid. Here we studied the lytic functions of PRD1. Using infected cells and plasmid-borne lysis genes, we demonstrated that a two-component lysis system (holin-endolysin) operates to release progeny phage particles from the host cell. Monitoring of ion fluxes and the ATP content of the infected cells allowed us to build a model of the sequence of lysis-related physiological changes. A decrease in the intracellular level of ATP is the earliest indicator of cell lysis, followed by the leakage of K+ from the cytosol approximately 20 min prior to the decrease in culture turbidity. However, the K+ efflux does not immediately lead to the depolarization of the cytoplasmic membrane or leakage of the intracellular ATP. These effects are observed only approximately 5 to 10 min prior to cell lysis. Similar results were obtained using cells expressing the holin and endolysin genes from plasmids.
The reaction catalyzed by P35 holin is:
autolysin (in) → autolysin (out)
P35 holin of phage PRD1 (Rydman and Bamford 2003; Ziedaite et al. 2005)
P35 protein of Bacteriophage PRD1 (Q3T4L9)
Phage holin of of Providencia stuartii
Putative holin of Xanthomonas phage vB_XSVEM_DIBBI
Putative holin (106 aas)
Putative holin of Pantoea stewartii
Uncharacterized protein of Methyloversatilis universalis
putative phage holin pg30
gp30 of Burkholderia phage Bcep43
Uncharacterized protein of 112 aas and 3 TMSs
UP of Parcubacteria group bacterium
Phage-related protein (105 aas)
Phage-related protein of Nitratiruptor sp. strain SB155-2
Uncharacterized protein of Vibrio mimicus
Putative holin of proteobacterial phage
Uncharacterized protein of Nitrosomonas eutropha
Putative holin of 134 aas and 3 TMSs.
Holin of E. coli
Putative holin of 107 aas and 3 TMSs.
Hol of Citrobacter sp. TSA-1
Phage holin family protein of 138 aas and 3 TMSs in a 1 + 2 TMS arrangement.
Holin of Marinomonas shanghaiensis
Holin, HolY of 103 aas and 3 TMSs. It is found in a holin-endolysin cassette in Y. enterocolitica, and has been adapted via evolution to export a large bacterial toxin (Sänger et al. 2023).
HolY of Yersinia enterocolitica
Holin, Stm0015, of 114 aas and 3 TMSs. This holin, together with a peptidoglycan hydrolase, Stm0016, comprises a secretion system (type 10) for an exo-chitinase of 699 aas (Stm0018) (partially homologous to the protein listed under TC# 9.B.29.2.7 (Chi1)).
Holin of Salmonella enterica (subsp. Typhimurium)
Uncharacterized protein of Desulfovibrio vulgaris
Putative holin of Aminobacterium colombiense
Uncharacterized protein of Dethiosulfovibrio peptidovorans
Putative holin of Jonquetella anthopi
Putative holin of Pyramidobacter piscolens