3kn8

Publication Abstract from PubMed

The periplasmic ferric binding protein A (FbpA) from H. 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 that transports iron into the cytoplasm. In this study we report on the properties of a series of site-directed mutants of two adjacent tyrosines involved in iron coordination, and demonstrate that, in contrast to mutation of equivalent residues of human transferrin N-lobe, 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 E. 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 protein 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 tyrosines 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 iron released by the outer membrane receptor complex.

The role of vicinal tyrosine residues in the function of Haemophilus influenzae ferric binding protein A.,Khambati HK, Moraes TF, Singh J, Shouldice SR, Yu RH, Schryvers AB Biochem J. 2010 Aug 27. PMID:20799927^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.