The PRD1 Phage P35 Holin (P35 Holin) Family (TC# 1.E.5) is a member of Holin Superfamily III. The prototype for this family is the lipid-containing PRD1 enterobacterial phage holin protein P35 (12.8 kDa; TC# 1.E.5.1.1) encoded by gene XXXV (orfT). It is a component of a typical holin-endolysin system which functions to lyse the host bacterial cell.
Contents
Structure
P35 holin (TC# 1.E.5.1.1) has 3 transmembrane segments (TMSs) with 5 positively charged residues between TMSs 1 and 2. It has 4 positively charged residues at the C-terminus. It is therefore thought that the N-terminus is in the periplasm and the C-terminus is in the cytoplasm. Homologues of 109 amino acyl residues (aas), which also have 3 putative TMSs, are encoded in the genomes of Xylella fastidiosa strains.
Function
PRD1 infects gram-negative cells harboring a conjugative IncP plasmid. Progeny phage particles are released from the host cell via a two-component lysis system (holin-endolysin). Ziedaite et al. (2005) monitored the ion flux and ATP content of infected cells to set up a model of the sequence of lysis-related physiological changes in the infected host. They showed 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 minutes prior to the decrease in culture turbidity. However, the K+ efflux did not immediately lead to the depolarization of the cytoplasmic membrane or leakage of the intracellular ATP. These effects were observed only approximately 5 to 10 minutes 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)