Calcium-binding sites selectivity

Numbers of Calcium-Binding Sites in Selected Metalloproteins... 

Factor IX is activated by factor XIa by cleavage of the Arg-146 and Arg-147 link to give factor IXa, and by further cleavage between Arg-181 and Val-182 in a metal-dependent reaction to give factor IXa,/3. All forms of factor IX have two classes of calcium-binding site. A protease from the venom of Vipera russelli is a coagulant, and activates both factors X and IX. This process requires divalent cations but is relatively non-selective. 

Fig. 10.T. Selective ion binding by human lysozyme upper left, wild type upper middle, Q86D upper right, A92D lower left, Q86D/A92D. The lower middle picture shows the calcium binding site in the Q86D/A92D mutant detected by X-ray, while the picture in lower right exhibits the binding-site found by the 3D-RISM theory...

HVA calcium channels are biochemically hetero-oligomeric complexes of five proteins encoded by four gene families (Fig. 1) The ax subunits of 190-250 kDa contain the voltage-sensor, the selectivity filter, the ion-conducting pore, the binding sites for most calcium... 

An ionophore is a compound that is capable of selectively carrying ions across a membrane. The ion fits into a specific binding site in a molecule that is hydrophobic enough to cross the membrane. There are calcium-specific ionophores, proton ionophores, sodium ionophores, etc. 

Monaghan, D. T., McMills, M. C., Chamberlin, A. R., Cotman, C. W. Synthesis of [3H]2-amino-4-phosphonobutyric acid and characterization of its binding to rat brain membranes a selective ligand for the chloride/calcium-dependent class of L-glutamate binding sites, Brain Res. 1983, 278, 137-144. 

Finally, novel nucleic acid catalysts have also been selected from random sequence pools (reviewed in Ref. 19). Joyce and co-workers have manipulated the function of the Group I self-splicing ribozyme, selecting variants that can utilize calcium or cleave DNA from partially randomized pools [20,21], Lorsch and Szostak [22] selected a polynucleotide kinase ribozyme from a completely random sequence pool that flanked a previously selected ATP binding site. Many of the novel ribozymes can catalyze reactions that are relevant to protein biosynthesis, bolstering arguments that translation may have arisen in a putative RNA world. For example, Lohse and Szostak [23] have selected ribozymes that can carry out an acyl transfer reaction, while Illangasekare et al. [24] have isolated a... 

One of the characteristics of protein calcium channels is their sensitivity to ablock by transition metal cations. Lanthanum is a particularly potent blocker. It is suggested that permeant and blocking ions compete for the common binding sites in the channels. The PolyP-PHB channel complexes are also blocked by transition metal cations in a concentration-dependent manner. A nearly complete block of single-channel currents was observed in the synthetic complexes at concentations > 0.1 mM La3+ (0.1 % of Ca2+) (Das et al., 1997). Evidently, PHB-PolyP complexes are versatile ion carriers whose selectivities may be modulated by small adjustments of the local pH. The results may be relevant to the physiological function of PHB-PolyP channels in bacteria and the role of PHBs and PolyPs in the Streptomyces lividans potassium channel (Das and Reusch, 2001). 

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