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The role of vicinal tyrosine residues in the function of Haemophilus influenzae ferric-binding protein A. Biochem J 2010; 432:57-64. [DOI: 10.1042/bj20101043] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The periplasmic FbpA (ferric-binding protein A) from Haemophilus influenzae plays a critical role in acquiring iron from host transferrin, shuttling iron from the outer-membrane receptor complex to the inner-membrane transport complex responsible for transporting iron into the cytoplasm. In the present study, we report on the properties of a series of site-directed mutants of two adjacent tyrosine residues involved in iron co-ordination, and demonstrate that, in contrast with mutation of equivalent residues in the N-lobe of human transferrin, the mutant FbpAs retain significant iron-binding affinity regardless of the nature of the replacement amino acid. The Y195A and Y196A FbpAs are not only capable of binding iron, but are proficient in mediating periplasm-to-cytoplasm iron transport in a reconstituted FbpABC pathway in a specialized Escherichia coli reporter strain. This indicates that their inability to mediate iron acquisition from transferrin is due to their inability to compete for iron with receptor-bound transferrin. Wild-type iron-loaded FbpA could be crystalized in a closed or open state depending upon the crystallization conditions. The synergistic phosphate anion was not present in the iron-loaded open form, suggesting that initial anchoring of iron was mediated by the adjacent tyrosine residues and that alternate pathways for iron and anion binding and release may be considered. Collectively, these results demonstrate that the presence of a twin-tyrosine motif common to many periplasmic iron-binding proteins is critical for initially capturing the ferric ion released by the outer-membrane receptor complex.
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Newstead S, Fowler PW, Bilton P, Carpenter EP, Sadler PJ, Campopiano DJ, Sansom MS, Iwata S. Insights into how nucleotide-binding domains power ABC transport. Structure 2009; 17:1213-22. [PMID: 19748342 PMCID: PMC2896483 DOI: 10.1016/j.str.2009.07.009] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2009] [Revised: 07/10/2009] [Accepted: 07/10/2009] [Indexed: 12/21/2022]
Abstract
The mechanism by which nucleotide-binding domains (NBDs) of ABC transporters power the transport of substrates across cell membranes is currently unclear. Here we report the crystal structure of an NBD, FbpC, from the Neisseria gonorrhoeae ferric iron uptake transporter with an unusual and substantial domain swap in the C-terminal regulatory domain. This entanglement suggests that FbpC is unable to open to the same extent as the homologous protein MalK. Using molecular dynamics we demonstrate that this is not the case: both NBDs open rapidly once ATP is removed. We conclude from this result that the closed structures of FbpC and MalK have higher free energies than their respective open states. This result has important implications for our understanding of the mechanism of power generation in ABC transporters, because the unwinding of this free energy ensures that the opening of these two NBDs is also powered.
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Affiliation(s)
- Simon Newstead
- Division of Molecular Biosciences, Membrane Protein Crystallography Group, Imperial College London, Exhibition Road, London SW7 2AZ, UK
| | - Philip W. Fowler
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
| | - Paul Bilton
- School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, UK
| | - Elisabeth P. Carpenter
- Division of Molecular Biosciences, Membrane Protein Crystallography Group, Imperial College London, Exhibition Road, London SW7 2AZ, UK
- Membrane Protein Laboratory, Diamond Light Source Ltd, Harwell Science and Innovation Campus, Chilton, Didcot OX11 ODE, UK
| | - Peter J. Sadler
- School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, UK
| | | | - Mark S.P. Sansom
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
| | - So Iwata
- Division of Molecular Biosciences, Membrane Protein Crystallography Group, Imperial College London, Exhibition Road, London SW7 2AZ, UK
- Membrane Protein Laboratory, Diamond Light Source Ltd, Harwell Science and Innovation Campus, Chilton, Didcot OX11 ODE, UK
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