Investigation of the metal-binding site 2 of Y. pestis YfeA protein: solution studies of Fe(ii), Mn(ii), and Zn(ii) complexes

YfeABCD is a metal-ion transport system found in Yersinia pestis, responsible for Fe(II) and Mn(II) uptake. YfeA is a periplasmic substrate-binding protein (SBP) that binds the metal ion in the periplasm and facilitates its transfer to the transmembrane YfeC and YfeD proteins. Interestingly, ITC and crystallographic data indicate that YfeA can also bind Zn(II) ions as a preferred substrate, even though the YfeABCD system most likely does not transport zinc. YfeA possesses two metal-binding sites. Site 2 was shown to bind Zn(II) and Mn(II), but not Fe(II) ions. In this work, we have investigated the metal-binding properties of a peptide model of YfeA Site 2. We have utilized a variety of physicochemical methods to characterize the stoichiometry, stability constants, and metal-binding residues in Fe(II), Mn(II), and Zn(II) complexes.