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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

 

 

This family belongs to the: Holin Superfamily III.

References associated with 1.E.5 family:

Rydman, P.S. and D.H. Bamford. (2003). Identification and mutational analysis of bacteriophage PRD1 holin protein P35. J. Bacteriol. 185: 3795-3803. 12813073
Ziedaite, G., R. Daugelavicius, J.K. Bamford, and D.H. Bamford. (2005). The Holin protein of bacteriophage PRD1 forms a pore for small-molecule and endolysin translocation. J. Bacteriol. 187: 5397-5405. 16030234