Metal-binding site

The dependence of chiral recognition on the formation of the diastereomeric complex imposes constraints on the proximity of the metal binding sites, usually either an hydroxy or an amine a to a carboxyHc acid, in the analyte. Principal advantages of this technique include the abiHty to assign configuration in the absence of standards, enantioresolve non aromatic analytes, use aqueous mobile phases, acquire a stationary phase with the opposite enantioselectivity, and predict the likelihood of successful chiral resolution for a given analyte based on a weU-understood chiral recognition mechanism. 

The incorporation of S-N chains between metal centres by the use of heteroaryl substituents in complexes of the type 14.7 has been proposed as a way to generate new materials that may function as molecular wires. However, the synthesis of thiazyl chains bearing metal-binding sites has yet to be achieved. 

PROTEIN STRUCTURE OF PEPTIDE DEFORMYLASES Three-dimensional Structure Metal-binding Site... 

Although native PDFs utilise Fe rather than Zn, the PDF metal-binding site is still very representative of a traditional zinc-metalloprotease [57], containing a conserved HEXXH motif. Crystal structures of the Fe ", Ni ", ... 

In the active site of PDF proteins, three substrate-binding pockets exist along with the metal-binding site. Using standard metalloprotease nomenclature. 

Smith, M. C., Engineering metal binding sites into recombinant proteins for facile purification, Ann. N. Y. Acad. Sci., 646, 315, 1991. 

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... 

Moving from single microorganisms to microbial communities, metals create selection pressure for microbes with cell structures that are less sensitive to metals. For example, mutations may occur that alter metal-binding sites of proteins without rendering the enzyme inactive. Another method for preventing metal toxicity is to produce excess amounts of the target so that there is an insufficient amount of metal to bind to all of the cellular molecules.4 35 53... 

Free, ionic species of metals are at their highest concentrations at lower pH, so metals tend to be more bioavailable under these conditions.121128 At acidic pH, more protons are available to saturate metal-binding sites.99 For example, metals are less likely to form insoluble precipitates with phosphates when the pH of the system is lowered because much of the phosphate has been protonated. Under basic conditions, metal ions can replace protons to form other species, such as hydroxo-metal complexes. Some of the hydroxo-metal complexes are soluble, such as those formed with cadmium, nickel, and zinc, whereas those formed with chromium and iron are insoluble. 

The fact that imidazole (Him) residues are particularly popular transition metal binding sites within metalloproteins is a major driving force for investigations of this heterocycle. The divalent... 

The Zn11 ion of angiotensin-converting enzyme (ACE) has been replaced by Co11 to give an active, chromophoric enzyme and inhibitor binding has been identified spectroscopically. Visible and MCD spectroscopy were used to characterize the catalytic metal binding site in the... 

Dendrimers with Metal-Binding Sites on the Surface... 

There is a plethora of examples representing dendrimers with metal-binding sites on the periphery. Polycarboxylates were the simplest, early examples [179], although dendrimers possessing more complicated ligand complexing centers have invariably been built via a convergent approach. 

Figure 6.15 Metal binding sites on the interior face of the B helix in FloLF. From Granier et al., 1998. Reproduced by permission of John Wiley Sons, Inc.

The important regulatory metal-binding site occupied in vivo by Fe2+ is not well characterized. The metal is bound in this site by at least two histidines and one carboxylate in an axially distorted octahedral environment (Althaus et ah, 1999), confirming earlier work (Hamed and Neilands, 1993). 

The crystal structures of DtxR and IdeR provide a detailed picture of this protein family (Figure 3.7, Plate 5). The N-terminal domain (residues 1-73) containing a helix-turn-helix motif binds a recognition nucleotide sequence of about 21 base pairs, as is nicely shown in a cocrystal of DNA and DtxR (Pohl et al., 1999). The central domain (74-140) has a function in dimerization the role of the third carboxy-terminal domain (141-230) is uncertain. Although metal-binding sites have been defined in these crystal structures, the mechanism by which metal binding causes the structural changes between apo- and holo-repressor is not clear. 

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