Metal-binding proteins, periplasmic

Some microbes are able to decrease the permeability of their membranes to prevent toxic metals from entering. If the toxic metals are not able to physically enter the cell, they will not be able to affect vital metal-sensitive structures, such as proteins. One way to prevent heavy metals from entering is by decreasing the production of membrane channel proteins.18 It is also possible for the metal-binding sites in the membrane and periplasm to be saturated with nontoxic metals.37 A third possibility is the formation of an extracellular polysaccharide coat, which binds and prevents metals from reaching the surface of the cell.24,38... 

The third redox-dependent process involved in metallocenter assembly requires changes to the protein, typically involving cysteine residues. For example, disulfide bonds that are spontaneously generated or enzymatically formed in periplasmic proteins must be reduced to create metal-binding thiolates or for cytochrome c biosynthesis. The opposite reaction, oxidation of cysteines during metallocenter assembly appears to be required for SODl activation. 

Beitle R.R. and Ataai M.M. One-step purification of a model periplasmic protein from inclusion bodies by its fusion to an effective metal-binding peptide, Biotechnol. Prog., 9, 64. 

Fig. 9. Alignment tree for metal-binding motifs of the three presumed mammalian copper ATPases, the two bacterial copper ATPases (CopA and SynA), along with bacterial cadmium ATPases (CadA and SynB) and mercury-binding periplasmic proteins, MerP, from plasmids RlOO and pDU1358. See text for literature citations...

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