Phage T5 Straight Tail Fiber Is a Multifunctional Protein Acting as a Tape Measure and Carrying Fusogenic and Muralytic Activities

Pascale Boulanger,Pierre Jacquot,Laure Plançon,Mohamed Chami,Andreas Engel,Claudine Parquet,Chantal Herbeuval,Lucienne Letellier

doi:10.1074/jbc.m800052200

Abstract

We report a bioinformatic and functional characterization of Pb2, a 121-kDa multimeric protein that forms phage T5 straight fiber and is implicated in DNA transfer into the host. Pb2 was predicted to consist of three domains. Region I (residues 1-1030) was mainly organized in coiled coil and shared features of tape measure proteins. Region II (residues 1030-1076) contained two alpha-helical transmembrane segments. Region III (residues 1135-1148) included a metallopeptidase motif. A truncated version of Pb2 (Pb2-Cterm, residues 964-1148) was expressed and purified. Pb2-Cterm shared common features with fusogenic membrane polypeptides. It formed oligomeric structures and inserted into liposomes triggering their fusion. Pb2-Cterm caused beta-galactosidase release from Escherichia coli cells and in vitro peptidoglycan hydrolysis. Based on these multifunctional properties, we propose that binding of phage T5 to its receptor triggers large conformational changes in Pb2. The coiled coil region would serve as a sensor for triggering the opening of the head-tail connector. The C-terminal region would gain access to the host envelope, permitting the local degradation of the peptidoglycan and the formation of the DNA pore by fusion of the two membranes.

Highlights

With the development of single phage particles studies [12, 13]
Escherichia coli cells led us to conclude that Pb2, the protein forming the 50-nm-long straight tail fiber [24], probably formed the DNA pore [25], a conclusion compatible with data showing that Pb2 isolated from the phage particle had a poreforming activity in planar lipid bilayers [26]
We show that its C-terminal region shares common features with fusogenic membrane peptides and carries a peptidoglycan hydrolase activity

Summary

Introduction

With the development of single phage particles studies [12, 13]. information on the in vivo DNA transport mechanism and on the phage/bacterial partners involved is still scarce. Escherichia coli cells led us to conclude that Pb2, the protein forming the 50-nm-long straight tail fiber [24], probably formed the DNA pore [25], a conclusion compatible with data showing that Pb2 isolated from the phage particle had a poreforming activity in planar lipid bilayers [26]. For determination of their hydrodynamic radius by dynamic light scattering, LUV were preincubated with Pb2-Cterm for 1 h (protein/lipid molar ratio 1:360) before measurements with a particle size analyzer (Brookhaven).

Results

Conclusion