Although the A-1 family SBPs has been extensively characterized they have been the subject of considerable controversy with respect to their metal binding properties. When bound to metal, by CD spectra TpTroA does not undergo structural changes, however, T. pallidum ZnuA undergoes conformational changes when Zn 2+ is loaded [31] . Synechocystis 6803 ZnuA displays concomitantly large conformational changes in two of its three chelating histidines due to the release of Zn because it possesses two Zn binding sites [27] . However, the second binding site is absent in other transporters (e.g., TpTroA), and therefore its exact biological function remains unclear [33] . To obtain further insight into the function of SsTroA, we determined the X-ray crystal structure of the Zn 2+ -bound form of the SsTroA at a resolution of 2.6 Å , and further characterized the recombinant SsTroA. Binding of divalent metal cations to SsTroA, induces a substantial conformational reorganization to a more ordered state. Our structural and functional data reported here lay out the scenario of SsTroA participating in S. suis divalent metal homeostasis.