Initiation of Phage Infection by Partial Unfolding and Prolyl Isomerization

Stephanie Hoffmann-Thoms,Ulrich Weininger,Barbara Eckert,Roman P Jakob,Johanna R Koch,Jochen Balbach,Franz X Schmid

doi:10.1074/jbc.m112.442525

Stephanie Hoffmann-Thoms, Ulrich Weininger + Show 5 more

Open Access

https://doi.org/10.1074/jbc.m112.442525

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Abstract

Infection of Escherichia coli by the filamentous phage fd starts with the binding of the N2 domain of the phage gene-3-protein to an F pilus. This interaction triggers partial unfolding of the gene-3-protein, cis → trans isomerization at Pro-213, and domain disassembly, thereby exposing its binding site for the ultimate receptor TolA. The trans-proline sets a molecular timer to maintain the binding-active state long enough for the phage to interact with TolA. We elucidated the changes in structure and local stability that lead to partial unfolding and thus to the activation of the gene-3-protein for phage infection. Protein folding and TolA binding experiments were combined with real-time NMR spectroscopy, amide hydrogen exchange measurements, and phage infectivity assays. In combination, the results provide a molecular picture of how a local unfolding reaction couples with prolyl isomerization not only to generate the activated state of a protein but also to maintain it for an extended time.

Highlights

Bacteriophage fd is activated for infection by partial unfolding and prolyl isomerization
Infection of Escherichia coli by the filamentous phage fd starts with the binding of the N2 domain of the phage gene-3-protein to an F pilus
The results provide a molecular picture of how a local unfolding reaction couples with prolyl isomerization to generate the activated state of a protein and to maintain it for an extended time

Summary

Background

Bacteriophage fd is activated for infection by partial unfolding and prolyl isomerization. Infection of Escherichia coli by the filamentous phage fd starts with the binding of the N2 domain of the phage gene-3-protein to an F pilus This interaction triggers partial unfolding of the gene-3-protein, cis 3 trans isomerization at Pro-213, and domain disassembly, thereby exposing its binding site for the ultimate receptor TolA. The results provide a molecular picture of how a local unfolding reaction couples with prolyl isomerization to generate the activated state of a protein and to maintain it for an extended time. The domain disassembly allows Pro-213 in the hinge (Fig. 1B) to isomerize from the strained cis to the more favorable trans conformation [9, 10]. trans-Pro-213 maintains fd-G3P in the open, infection-competent conformation for an extended time and allows the N1 domain to bind to its receptor

The following designations are used throughout this study

EXPERIMENTAL PROCEDURES

RESULTS

D28 N67 M176

DISCUSSION