Topological dynamics of holins in programmed bacterial lysis

doi:10.1073/pnas.0600943103

Topological dynamics of holins in programmed bacterial lysis

Department of Biochemistry and Biophysics, Texas A&M University, 2128 TAMU, College Station, TX 77843-2128

Edited by Cornelia I. Bargmann, The Rockefeller University, New York, NY, and approved October 25, 2006 (received for review February 3, 2006)

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. S²¹68, the holin of phage 21, has two transmembrane domains (TMDs) with a predicted N-in, C-in topology. Surprisingly, TMD1 of S²¹68 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 S²¹68 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.

Footnotes

^†To whom correspondence should be addressed. E-mail: ryland{at}tamu.edu
Author contributions: T.P., D.K.S., J.F.D., and R.Y. designed research; T.P. and J.F.D. performed research; T.P. and J.F.D. contributed new reagents/analytic tools; T.P., D.K.S., J.F.D., and R.Y. analyzed data; and T.P., D.K.S., and R.Y. wrote the paper.
↵*Present address: Department of Biochemistry and Microbiology, University of Georgia, Athens, GA 30602.
The authors declare no conflict of interest.
This article is a PNAS direct submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0604444103/DC1.
Abbreviations:

DNP,

dinitrophenol;

TCA,

trichloroacetic acid;

TMD,

transmembrane domain.