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J. Biol. Chem., Vol. 283, Issue 20, 13556-13564, May 16, 2008
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1
From the
Institut de Biochimie et Biophysique Moléculaire et Cellulaire, Université Paris-Sud,
CNRS, UMR 8619, Orsay F-91405, France, and ¶ME Müller Institute, Biozentrum, University of Basel, Basel CH-4056, Switzerland
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
-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 β-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.
Received for publication, January 3, 2008 , and in revised form, March 14, 2008.
* This work was supported in part by the CNRS program "Dynamique et Réactivité des Assemblages Biologiques" and by a Ph.D. fellowship from the Ministére de l'Education Nationale de la Recherche et de la Technologie (to P. J.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 To whom correspondence should be addressed: IBBMC, Bat 430, Université Paris Sud, Orsay, F-91405. Fax: 33-1-69-85-37-15; E-mail: lucienne.letellier{at}u-psud.fr.
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