Selective Binding of Amino Acids

So far we now have available a very efficient binding motif for carboxylates. For use of this binding motif as a building block in modular peptide receptors it is also 

---

It is not clear why some organisms have two 14-3-3 isoforms while others have up to 12. Binding 14-3-3 inhibits the plant enzyme nitrate reductase and there appears to be no selectivity between plant 14-3-3 isoforms in fact yeast and human isoforms appear to work equally as well in vitro. The best example where selectivity has been demonstrated is human 14-3-3o. 14-3-3o Preferential homodimerizes with itself and crystallization revealed a structural basis for this isoform s dimerization properties as well as for its specific selectivity for target binding proteins. Here partner specificity is the result of amino acid differences outside of the phosphopeptide-binding cleft. 

The addition of ammonia to the variety of acids derivable from either the breakdown of glucose, glycolysis, or of the pentose shunt reaction products, ribose and NADPH, and from the citrate cycle, gives the amino acids (see Table 4.7 and Figure 4.4) Polymerisation of amino acids in cells gives proteins. In some of the amino acids sulfur and selenium can be incorporated easily. We assume NH3 was present. (Note that Se is in a coded amino acid not in Table 4.7.) Some selective metal-binding properties can be seen in Table 4.7, but amino acid carboxylates can bind all. 

Other potent peptide mimetic NS3 protease inhibitors have been reported that incorporate a serine trap on the C-terminal end of the peptide. Thus, the inhibitory activity of telaprevir (VX-950, 59), (7nM vs. NS3, 300 nM vs. the la replicon) is based on truncation of the polypeptide substrate, maximizing binding by alteration of amino acids at the scissile site, and capping both N- and C-terminal ends, the latter with a known dicarbonyl serine trap. This compound has exhibited impressive antiviral activity in animals, and showed a 4.4 log drop in viral load in genotype 1-infected patients in a Phase lb clinical trial [110]. Telaprevir is expected to enter Phase 3 clinical trials in 2007. Additional bicyclo-proline-based P2 tetrapeptides, represented by analog 60 (Kj = 22 nM), have been explored. Although the compounds are selective inhibitors of NS3, little or no cell-based replicon activity was reported, presumably due to poor cellular permeability [111-114], A diastereomer of telaprevir, has been reported to inhibit the replicon with an EC50 of 0.55 pM [115]. 

Some authors based their approach to selective binding of the more lipophilic a-amino acids in water on hydrophobic effects using water-soluble, cavity-containing cyclophanes for the inclusion of only the apolar tail under renouncement of any attractive interaction of the hosts with the zwitterionic head . Kaifer and coworkers made use of the strong affinity of Stoddart s cyclobis(paraquat-p-phenylene) tetracation 33 for electron-rich aromatic substrates to achieve exclusive binding of some aromatic a-amino acids (Trp, Tyr) in acidic aqueous solution [48]. Aoyama et al. reported on selectivities of the calix[4]pyrogallolarene 34 with respect to chain length and t-basicity of aliphatic and aromatic amino acids, respectively [49]. Cyclodextrins are likewise water-soluble and provide a lipophilic interior. Tabushi modified )S-cyclodextrin with a 1-pyrrolidinyl and a carboxyphenyl substituent to counterbalance the... 

---