title: Periplasmic domains define holin-antiholin interactions in t4 lysis inhibition.
abstract: Bacteriophage T4 effects host lysis with a holin, T, and an endolysin, E. T and E accumulate in the membrane and cytoplasm, respectively, throughout the period of late gene expression. At an allele-specific time, T triggers to disrupt the membrane, allowing E to enter the periplasm and attack the peptidoglycan. T triggering can be blocked by secondary infections, leading to the state of lysis inhibition (LIN). LIN requires the T4 antiholin, RI, and is sensitive to the addition of energy poisons. T is unusual among holins in having a large C-terminal periplasmic domain. The rI gene encodes a polypeptide of 97 residues, of which 72 are predicted to be a periplasmic domain. Here, we show that the periplasmic domain of RI is necessary and sufficient to block T-mediated lysis. Moreover, when overexpressed, the periplasmic domain of T (T(CTD)) was found to abolish LIN in T4 infections and to convert wild-type (wt) T4 plaques from small and fuzzy edged to the classic "r" large, sharp-edged plaque morphology. Although RI could be detected in whole cells, attempts to monitor it during subcellular fractionation were unsuccessful, presumably because RI is a highly unstable protein. However, fusing green fluorescence protein (GFP) to the N terminus of RI created a more stable chimera that could be demonstrated to form complexes with wild-type T(CTD) and also with its LIN-defective T75I variant. These results suggest that the function of the unusual periplasmic domain of T is to transduce environmental information for the real-time control of lysis timing.
authors.affiliation: Department of Biochemistry and Biophysics, Texas A&M University, 2128 TAMU, College Station, TX 77843-2128, USA.
authors.forename: Tram Anh T
authors.initials: TA
authors.lastname: Tran
authors.forename: Douglas K
authors.initials: DK
authors.lastname: Struck
authors.forename: Ry
authors.initials: R
authors.lastname: Young
mesh_terms: D000595:Amino Acid Sequence; D001433:Bacteriolysis / Q000502:physiology*; D017122:Bacteriophage T4 / Q000235:genetics* / Q000254:growth & development; D010450:Endopeptidases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000821:virology*; D008969:Molecular Sequence Data; D033903:Periplasmic Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
chemical_list: D033903:Periplasmic Proteins; D011993:Recombinant Fusion Proteins; D014764:Viral Proteins; C120332:holin t protein, Enterobacteria phage T4; C078762:lysis protein T, bacteriophage T4; D010450:Endopeptidases; C001143:endolysin