Article ; Online: HDX-MS performed on BtuB in
Proceedings of the National Academy of Sciences of the United States of America
2022 Volume 119, Issue 20, Page(s) e2119436119
Abstract: To import large metabolites across the outer membrane of gram-negative bacteria, TonB-dependent transporters (TBDTs) undergo significant conformational change. After substrate binding in BtuB, the Escherichia coli vitamin B12 TBDT, TonB binds and couples ...
Abstract | To import large metabolites across the outer membrane of gram-negative bacteria, TonB-dependent transporters (TBDTs) undergo significant conformational change. After substrate binding in BtuB, the Escherichia coli vitamin B12 TBDT, TonB binds and couples BtuB to the inner-membrane proton motive force that powers transport [N. Noinaj, M. Guillier, T. J. Barnard, S. K. Buchanan, Annu. Rev. Microbiol. 64, 43–60 (2010)]. However, the role of TonB in rearranging the plug domain of BtuB to form a putative pore remains enigmatic. Some studies focus on force-mediated unfolding [S. J. Hickman, R. E. M. Cooper, L. Bellucci, E. Paci, D. J. Brockwell, Nat. Commun. 8, 14804 (2017)], while others propose force-independent pore formation by TonB binding [T. D. Nilaweera, D. A. Nyenhuis, D. S. Cafiso, eLife 10, e68548 (2021)], leading to breakage of a salt bridge termed the “Ionic Lock.” Our hydrogen–deuterium exchange/mass spectrometry (HDX-MS) measurements in E. coli outer membranes find that the region surrounding the Ionic Lock, far from the B12 site, is fully destabilized upon substrate binding. A comparison of the exchange between the B12-bound and the B12+TonB–bound complexes indicates that B12 binding is sufficient to unfold the Ionic Lock region, with the subsequent binding of a TonB fragment having much weaker effects. TonB binding accelerates exchange in the third substrate-binding loop, but pore formation does not obviously occur in this or any region. This study provides a detailed structural and energetic description of the early stages of B12 passage that provides support both for and against current models of the transport process. |
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MeSH term(s) | Allosteric Regulation ; Bacterial Outer Membrane Proteins/chemistry ; Bacterial Outer Membrane Proteins/metabolism ; Biological Transport ; Escherichia coli/metabolism ; Escherichia coli Proteins/chemistry ; Escherichia coli Proteins/metabolism ; Hydrogen Deuterium Exchange-Mass Spectrometry ; Membrane Proteins/chemistry ; Membrane Proteins/metabolism ; Membrane Transport Proteins/chemistry ; Membrane Transport Proteins/metabolism ; Protein Binding ; Protein Domains ; Protein Folding ; Vitamin B 12/metabolism |
Chemical Substances | Bacterial Outer Membrane Proteins ; BtuB protein, E coli ; Escherichia coli Proteins ; Membrane Proteins ; Membrane Transport Proteins ; tonB protein, E coli ; Vitamin B 12 (P6YC3EG204) |
Language | English |
Publishing date | 2022-05-12 |
Publishing country | United States |
Document type | Journal Article |
ZDB-ID | 209104-5 |
ISSN | 1091-6490 ; 0027-8424 |
ISSN (online) | 1091-6490 |
ISSN | 0027-8424 |
DOI | 10.1073/pnas.2119436119 |
Database | MEDical Literature Analysis and Retrieval System OnLINE |
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