Topological dynamics of holins in programmed bacterial lysis

Abstract

The fate of phage-infected bacteria is determined by the holin, a small membrane protein that triggers to disrupt the membrane at a programmed time, allowing a lysozyme to attack the cell wall. S 21 68, the holin of phage 21, has two transmembrane domains (TMDs) with a predicted N-in, C-in topology. Surprisingly, TMD1 of S 21 68 was found to be dispensable for function, to behave as a SAR (''signal-anchor-release'') domain in exiting the membrane to the periplasm, and to engage in homotypic interactions in the soluble phase. The departure of TMD1 from the bilayer coincides with the lethal triggering of the holin and is accelerated by membrane depolarization. Basic residues added at the N terminus of S 21 68 prevent the escape of TMD1 to the periplasm and block hole formation by TMD2. Lysis thus depends on dynamic topology, in that removal of the inhibitory TMD1 from the bilayer frees TMD2 for programmed formation of lethal membrane lesions.bacteriophage ͉ GxxxG motif ͉ SAR domain ͉ transmembrane domain

Structure of the lethal phage pinhole

“…The pinholins are a new class of holins that forms small holes using only a single TMD (7). Interest in the prototype pinholin, S 21 68, was piqued by the simplicity of its primary structure, by evidence indicating that its N-terminal TMD was required to exit the bilayer for triggering to occur, and by its near identity with the holin of the prophage 933w, which controls release of Stx toxin during E. coli O157:H7 infections (Fig.…”

“…TMD1 is not only dispensable for hole-formation and lysis, but in fact, is itself a SAR domain that must exit the bilayer in order for TMD2 to be competent for hole-formation (Fig. 1B) (7). This property is most dramatically illustrated by the modified allele irsS 21 68, which encodes the S 21 68 with the irs epitope, containing two positively-charged residues, added to the N terminus.…”

“…This property is most dramatically illustrated by the modified allele irsS 21 68, which encodes the S 21 68 with the irs epitope, containing two positively-charged residues, added to the N terminus. Because the extra charges prevent TMD1 from exiting the membrane, the irsS 21 68 protein has an absolute lysis-defective phenotype (7). In this article, we present biochemical, ultrastructural, and computational studies of the elements of S 21 68 that are involved in the membrane lesion.…”

“…Recently, an alternative and remarkably different class of holin-endolysin systems has emerged (6)(7)(8). This class, represented by the lambdoid bacteriophage 21, utilizes endolysins having novel N-terminal secretory signals called signal-anchor release (SAR) domains.…”

Roles of bacteriophage GVE2 endolysin in host lysis at high temperatures

“…The antiholins are identical to the holins except for two or more additional amino acids present on the N terminus of antiholins. Antiholins can regulate the hole forming by inhibiting holin oligomerization (Pang et al, 2010;Park et al, 2006). So far, considerable advances have been made in revealing the lysis process of host bacteria by double-stranded DNA phages.…”