1.E.20 The Pseudomonas aeruginosa Hol Holin (Hol Holin) Family
The hol gene (PRF9) product (117 aas) of Pseudomonas aeruginosa PAO1 exhibits a hydrophobicity profile similar to holins of P2 and φCTX phages with two peaks of hydrophobicity that might correspond to either one or two TMSs. Hol functions in conjunction with the lytic enzyme, Lys (PRF24; BAA83168, 209 aas). Hol by itself, when expressed in a broad host-range expression vector under IPTG control exhibited strong lytic activity in both P. aeruginosa and E. coli. Expression of the lys gene plus chloroform (but not minus chloramphenicol) yielded cell lysis. In another expression vector, coexpression of hol and lys induced lysis under conditions where neither gene alone induced lysis (Nakayama et al., 2000). The hol-lys gene system therefore is believed to constitute a chromosomally-encoded autolysis system.
The reaction probably catalyzed by Hol is:
Autolysin (Lys)in → Autolysin (Lys)out
Holin, Hol (Nakayama et al. 2000)
Hol of Pseudomonas aeruginosa PAO1
Pyocin R2_PP holin
Pyocin R2-PP holin of Pseudomonas aeruginosa
SH3 type 3 domain-containing protein
SHE type 3 domain-containing protein of Brucella sp.
Holin of 115 aas and 3 TMSs, pyocin R2 holin. Functions in DNA release within biofilms (Wang et al. 2016). A gene cluster encoding a bacteriophage-derived pyocin and its lysis cassette was upregulated in phenozine producing strains. A holin encoded in this gene cluster was found to contribute to the release of eDNA in biofilm matrices, demonstrating that the influence of the phenozine, 2-OH-PCA, on eDNA production is due in part to cell autolysis as a result of pyocin production and release (Wang et al. 2016).
Holin of Pseudomonas chlororaphis