Abstract
BackgroundHolins are a group of phage-encoded membrane proteins that control access of phage-encoded endolysins to the peptidoglycan, and thereby trigger the lysis process at a precise time point as the 'lysis clock'. SMP is an isolated and characterized Streptococcus suis lytic phage. The aims of this study were to determine the holin gene, HolSMP, in the genome of SMP, and characterized the function of holin, HolSMP, in phage infection.ResultsHolSMP was predicted to encode a small membrane protein with three hydrophobic transmembrane helices. During SMP infections, HolSMP was transcribed as a late gene and HolSMP accumulated harmlessly in the cell membrane before host cell lysis. Expression of HolSMP in Escherichia coli induced an increase in cytoplasmic membrane permeability, an inhibition of host cell growth and significant cell lysis in the presence of LySMP, the endolysin of phage SMP. HolSMP was prematurely triggered by the addition of energy poison to the medium. HolSMP complemented the defective λ S allele in a non-suppressing Escherichia coli strain to produce phage plaques.ConclusionsOur results suggest that HolSMP is the holin protein of phage SMP and a two-step lysis system exists in SMP.
Highlights
Holins are a group of phage-encoded membrane proteins that control access of phage-encoded endolysins to the peptidoglycan, and thereby trigger the lysis process at a precise time point as the ‘lysis clock’
The results of PredictProtein, TmHMM and SOSUI analysis suggested that HolSMP is a membrane protein with traits typical of a holin
The result of the complementation test indicated that HolSMP is able to function as a holin protein and complement an S-negative lysis-defective l phage mutant. From these results, protein HolSMP has been identified for the first holin of S. suis bacteriophage
Summary
Holins are a group of phage-encoded membrane proteins that control access of phage-encoded endolysins to the peptidoglycan, and thereby trigger the lysis process at a precise time point as the ‘lysis clock’. The aims of this study were to determine the holin gene, HolSMP, in the genome of SMP, and characterized the function of holin, HolSMP, in phage infection. By accumulating and forming lesions in the cytoplasmic membrane, holins control access of phageencoded endolysins to the peptidoglycan and thereby trigger lysis of the host cell at a precise time point. This process determines the length of the infection cycle and is known as the ‘lysis clock’. At least one hydrophobic transmembrane domain (TMD) occurs in all holins
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