Structure and Metal binding Characterization of the C-terminal Mellochaperone Domain of Membrane Fusion Protein SilB from Cupriavidus metallidurans CH34

In Cupriavidus metallidurans CH34, a model organism for heavy metal resistance studies, the sil determinant is potentially involved in the efflux of of silver and copper ions. Proteins SilA, SilB, SilC form a resistance/nodulation/cell division (RND)-based transport system in which SilB is the periplasmic adaptor protein belonging to the membrane fusion protein family. In addition sto the four domains typical of known MFPs, SilB has a fifth additional C-terminal domain , SilB440-521. Structure and backbone of SilB440-521 have been investigated using NMR, and the residues of the metal site have been from 15N- and 13C-edited HSQC spectra.The solution structure and additional metal binding experiments that this C-terminal domain folds independantly of the rest of the protein and has a conformation and a Ag+ /Cu+ binding specificity similar to those determined for CusF from Escherichia coli. The samll protein CusF plays a role in metal trafficking in the periplasm. This suggests a potential metallochaperone role for SilB440-521 that is discussed in the context of simultaneous expression of different determinants involved in copper resistance in C.metallidurans CH34