Metal-ion binding sites

In Chapter 2 we have described the nature and strengths of metal ion binding sites in the equation for complex formation in chemistry... 

An alternative approach is that adopted by Horrocks and co-workers, where the aromatic residues in metal-binding proteins are used as sensitizers. Since the distance between the metal and the donor is effectively fixed, this provides a rigid scaffold for the experiment, and the absence of a directly conjugated pathway between the metals means that Forster (through space) energy transfer can be assumed. The r-6 distance-dependence of this means that the extent of sensitized emission from the lanthanide ion provides information on the spatial relationship between the metal-ion binding site (lanthanide ions often bind at Ca2+ sites) and nearby aromatic residues. 58-60... 

The availability of different metal ion binding sites in 9-substituted purine and pyrimidine nucleobases and their model compounds has been recently reviewed by Lippert [7]. The distribution of metal ions between various donor atoms depends on the basicity of the donor atom, steric factors, interligand interactions, and on the nature of the metal. Under appropriate reaction conditions most of the heteroatoms in purine and pyrimidine moieties are capable of binding Pt(II) or Pt(IV) [7]. In addition, platinum binding also to the carbon atoms (e.g. to C5 in 1,3-dimethyluracil) has been established [22]. However, the strong preference of platinum coordination to the N7 and N1 sites in purine bases and to the N3 site in pyrimidine bases cannot completely be explained by the negative molecular electrostatic potential associated with these sites [23], Other factors, such as kinetics of various binding modes and steric factors, appear to play an important role in the complexation reactions of platinum compounds. 

Voss, J., Hubbell, W. L., and Kaback, H. R. (1995) Distance determination in proteins using designed metal ion binding sites and site-directed spin labeling application to the lactose permease of Escherichia coli. Proc. Natl. Acad. Sci. USA 92, 12300-12303. 

Sheikh, S. P, Zvyaga, T. A., Lichtarge, O., Sakmar, T. P., and Bourne, H. R. (1996) Rhodopsin activation blocked by metal-ion-binding sites linking transmembrane helices C and F. Nature 383, 347-350. 

Figure 3.5 Structure (a), porphyrin (b) and metal ion-binding sites (c) in Bacillus subtilis fer-rochelatase. In (c) the two metal ions are a Zn2+ ion (grey) and a fully hydrated Mg2+ ion. The side chains of Glu272, Asp 268 and Glu264 are aligned along a tr-helix (green). (From Al-Karadaghi et al., 2006. Copyright 2006, with permission from Elsevier.)...

The use of the upper rim of calix 4 arcncs, blocked in the cone conformation, as convenient platforms for the introduction of metal ion binding sites is well documented [26e,291. Table 5.9 shows the catalytic performances of regioisomeric vicinal 21-Ba2 and distal 22-Ba2, and of the m-xylylene derivative 17-Ba2 in the basic ethanolysis of esters 14 and 23-25 [30]. 

Thus, we have determined the distances between the adenylyl moiety and the two divalent metal ion binding sites on glutamine synthetase by 13C and 3 P NMR, spin-labeled EPR, and fluorescence energy transfer methods. The results obtained from each method are in good agreement. The data show that the adenylyl regulatory site is close to the catalytic site (12-20 A). Additional data on the rotational correlation time of the adenyl derivatives reveal that the adenylyl site is located on the surface of the enzyme. 

Figure 9 Intramolecular charge transfer (ICT) emission evolves from a localized excited state (LE). If a metal ion-binding site is present (indicated by the half-circle), ICT emission may be stabilized or destabilized depending on whether the metal ion ( ) binds is at the electronegative or electropositive end of the Jt-aromatic system.

Kisseleva, N., Kraut, S., Jaschke, A., and Schiemann, O. (2007). Characterizing multiple metal ion binding sites within a ribozyme by cadmium-induced EPR silencing. HFSPJ. 

Specific metal ion binding sites are directly observed in the crystal structures of hammerhead ribozymes [18], P4—P6 domain of Tetrahymena group I intron [19], transfer (tRNA) [20], GAAA tetraloop receptor [21], sarcin-ricin loop [22], and MMTV pseudoknots [23], for example. High... 

---