Metal chaperones

COXl 7 copper carrying molecule for the mitochondria IMS intermembrane space of mitochondria, lying between the inner and outer membranes of this organelle Metal chaperone molecule that binds a specific metal and helps insert this ion into the metal binding site of a metalloprotein... 

In addition to the membrane bound transporters, the delivery of certain metals to their cognate metalloprotein involves the action of highly specific metal chaperone or metaUochaperone proteins. These metal carriers are often soluble, as opposed to membrane associated, and act to directly insert the metal into the proper site of the metalloprotein. 

Overall, a metal ion is not permitted to freely move about within a cell, but instead is personally escorted to its destination through the combined action of metal transporters and metal chaperones working in concert. This process of moving metals inside cells is commonly referred to as metal trafficking . And many such highways exist in eukaryotic cells (reviewed in ). 

Figure 1 XAS spectrum for the Fe(fl)-metal chaperone protein yeast frataxin with spectral regions labeled for clarity. Dashed line separates the regions...

Some of these helper proteins such as UreE and HybB bind the nickel cations meant for incorporation into nickel-containing enzymes (Lee et al. 1993, Park et al. 1994, Lee etal., 2002b, Song etal. 2001, Remaut etal. 2001). These proteins act as metal chaperones, which discriminate between anabolic nickel that serves as a trace element and toxic nickel. Ni(II) binds to polyphosphate, like many other divalent cations (Gonzalez and Jensen 1998), but... 

A notable recently identified exception is copper (see Chapter 13) for which specific chaperone proteins deliver the metal to individual copper-dependant proteins (Harrison et al., 1999). 

Cysteine can bind to either one or two metal ions, and is frequently found as a ligand to iron (in Fe-S clusters—see later) and to Cu+ (for example in the copper chaperones, which transfer copper to specific copper-binding proteins). Histidine can bind metal ions in two... 

The hype proteins are all relatively small proteins of between 75 and 108 amino acid residues which do not contain obvious metal-binding motifs. As will be discussed below (Section 4.5), these proteins may act as chaperones for hydrogenases during the process of matnration. This has been suggested from the studies of the interaction... 

One group is the metallothioneins, which bind metals, another is the heat-shock proteins (hsps). These latter ones are called "molecular chaperones" and are involved in, for example,... 

---