2x9a
crystal structure of g3p from phage IF1 in complex with its coreceptor, the C-terminal domain of TolA
Structural highlights
FunctionG3P_BPIF1 Plays essential roles both in the penetration of the viral genome into the bacterial host via pilus retraction and in the extrusion process. During the initial step of infection, G3P mediates adsorption of the phage to its primary receptor, the tip of host I-pilus. Subsequent interaction with the host entry receptor tolA induces penetration of the viral DNA into the host cytoplasm. In the extrusion process, G3P mediates the release of the membrane-anchored virion from the cell via its C-terminal domain (By similarity). Publication Abstract from PubMedThe filamentous phage fd uses its gene 3 protein (G3P) to target Escherichia coli cells in a two-step process. First, the N2 domain of G3P attaches to an F pilus, and then the N1 domain binds to TolA-C. N1 and N2 are tightly associated, rendering the phage robust but noninfectious because the binding site for TolA-C is buried at the domain interface. Binding of N2 to the F pilus initiates partial unfolding, domain disassembly, and prolyl cis-to-trans isomerization in the hinge between N1 and N2. This activates the phage, and trans-Pro213 maintains this state long enough for N1 to reach TolA-C. Phage IF1 targets I pili, and its G3P contains also an N1 domain and an N2 domain. The pilus-binding N2 domains of the phages IF1 and fd are unrelated, and the N1 domains share a 31% sequence identity. We show that N2 of phage IF1 mediates binding to the I pilus, and that N1 targets TolA. Crystallographic and NMR analyses of the complex between N1 and TolA-C indicate that phage IF1 interacts with the same site on TolA-C as phage fd. In IF1-G3P, N1 and N2 are independently folding units, however, and the TolA binding site on N1 is permanently accessible. Activation by unfolding and prolyl isomerization, as in the case of phage fd, is not observed. In IF1-G3P, the absence of stabilizing domain interactions is compensated for by a strong increase in the stabilities of the individual domains. Apparently, these closely related filamentous phages evolved different mechanisms to reconcile robustness with high infectivity. The Filamentous Phages fd and IF1 Use Different Mechanisms to Infect Escherichia coli.,Lorenz SH, Jakob RP, Weininger U, Balbach J, Dobbek H, Schmid FX J Mol Biol. 2010 Nov 24. PMID:21110981[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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