Cation sequences proteins

Cathepsin G, a cationic, glycosylated protein of relative molecular mass -27 kDa, exists in four isoforms (25-29 kDa) that are identical in amino acid sequence but differ in levels of glycosylation. It is a component of azurophilic granules and present in human neutrophils at 1.5-3 jug/106 cells, but at lower levels in monocytes. cDNA has been cloned and sequenced (and the amino acid sequence predicted), and the gene has been localised to chromosome 14ql 1.2. The gene comprises five exons and four introns, a structure similar to that of the elastase gene. 

Since the sequence is also Li ) Na ) K in the ion spectrum of negative proteins and these ions bring about fairly strong complex relations in this case also, the interpretation with regard to the cation sequence in the suppression of the tricomplex flocculation is exactly the same as that described in detail above. For the anion sequence, arguing similarly as above, the ion sequence in the ion spectrum of gelatin (p. 299, Fig. 22) is to be expected. This is indeed the same as that found experimentally in the suppression of the tricomplex. 

A superfamily of cation channels conserved in mammals, flies, worms and yeast. The various TRP-proteins bear-sequence and predicted structural similarities to the founding member of this superfamily, transient receptor-potential (TRP), a light activated cation channel in the Dmsophila photoreceptor. 

Figure 2.6. LC-tandem mass spectrometry to examine complex mixtures. The mixture of many different proteins is digested to yield peptides and the peptides are resolved into fractions hy cation exchange chromatography followed by reverse phase chromatography. The fractionation steps resolve the peptides into fractions that he processed hy tandem mass spectrometry to yield sequence information suitable for database searching.

The Fur protein from E. coli was isolated in one step due to its high affinity for metal-chelate columns loaded with zinc. In DNase footprinting experiments, the Fur protein was shown to bind DNA in the promoter region of several iron-regulated genes. The consensus sequence, called the Fur box, is GATAATGATAATCATT ATC. In vitro binding is dependent on the divalent cations Co2+ Mn2+ /s Cd2+ Cu2+ at 150 iM, while Fe2+ seemed to be less active at this concentration, probably due to oxidation to Fe3+ (De Lorenzo et al., 1987). The unspecificity for divalent metals observed in vitro shows that the cells have to select the ions transported carefully and have to balance their active concentrations. In addition, it is a caveat for the experimenter to test a hypothesis on metal-ion specificity not only in vitro, but also in vivo. 

---