PDBsum entry 1zzv

Membrane protein, metal transport

PDB id: 1zzv

Contents

Protein chain

80 a.a.

References listed in PDB file

Key reference

Title

Signal transduction pathway of tonb-Dependent transporters.

Authors

A.D.Ferguson, C.A.Amezcua, N.M.Halabi, Y.Chelliah, M.K.Rosen, R.Ranganathan, J.Deisenhofer.

Ref.

Proc Natl Acad Sci U S A, 2007, 104, 513-518. [DOI no: 10.1073/pnas.0609887104]

PubMed id

17197416

Abstract

Transcription of the ferric citrate import system is regulated by ferric citrate binding to the outer membrane transporter FecA. A signal indicating transporter occupancy is relayed across the outer membrane to energy-transducing and regulatory proteins embedded in the cytoplasmic membrane. Because transcriptional activation is not coupled to ferric citrate import, an allosteric mechanism underlies this complex signaling mechanism. Using evolution-based statistical analysis we have identified a sparse but structurally connected network of residues that links distant functional sites in FecA. Functional analyses of these positions confirm their involvement in the mechanism that regulates transcriptional activation in response to ferric citrate binding at the cell surface. This mechanism appears to be conserved and provides the structural basis for the allosteric signaling of TonB-dependent transporters.

Figure 1.
Fig. 1. Ferric citrate-mediated conformational changes in FecA. (A) Superposition of FecA without (yellow) and with (blue) ferric citrate (magenta). The front of the barrel has been removed for clarity. The signaling domain is attached to the plug by a flexible linker (dashed line). Binding ferric citrate causes conformational changes in the barrel and the translation of several apical loops of the plug toward the ferric citrate molecule. (B) Close-up of the extracellular pocket as seen from the solvent. Ferric citrate binding causes conformational changes in L7 and L8 and the closing of the extracellular pocket. (C) Close-up of the periplasmic pocket as seen from the periplasm. Binding ferric citrate induces the unwinding of the switch helix and changes in the relative position of the TonB-box. All figures were prepared with PyMOL (41).

Figure 3.
Fig. 3. Coevolving networks of the barrel and plug and the signaling domain link distant functional sites within FecA. (A) Ribbon diagrams of the unliganded (yellow) and liganded (blue) conformations of FecA. Residues T138, R365, R380, R438, and Q570 form the ferric citrate binding site (red sticks) and are each located within 3.5 Å of the ferric citrate molecule (magenta CPK model). The SCA-derived network of the barrel and plug has been mapped onto the structure with the van der Waals surfaces associated with these residues colored blue. The locations of those point mutations described in Table 1 are shown in red. (B–D) Serial sections through FecA as viewed from the solvent. (E and F) Ribbon diagrams of the signaling domain of FecA (silver). The SCA-derived network of the signaling domain has been mapped onto the structure with the van der Waals surfaces associated with these residues colored blue. The locations of those point mutations described in Table 1 are shown in red.