Crystal structure and NMR conformation of a cyclic pseudotetrapeptide containing urethane backbone linkages

Synthetic and structural routes for the rational conversion of peptides into small molecules

The demand for modified peptides with improved stability profiles and pharmacokinetic properties is driving extensive research effort in this field. The conversion of peptides into organic molecules, as traditional drugs, is a long and puzzled way. Many and versatile approaches have been described for designing peptide mimetics: the substitution of natural residues with modified amino acids and the rigidification and modification of the backbone are the main structural and chemical routes walked in medicinal chemistry. All of these strategies have been successfully applied to obtain active new compounds in molecular biology, drug discovery and design. Here we propose a panoramic review of the most common methods for the preparation of modified peptides and the most interesting findings of the last decade.

cAMP activation of PKA defines an ancient signaling mechanism

cAMP and the cAMP binding domain (CBD) constitute a ubiquitous regulatory switch that translates an extracellular signal into a biological response. The CBD contains alpha- and beta-subdomains with cAMP binding to a phosphate binding cassette (PBC) in the beta-sandwich. The major receptors for cAMP in mammalian cells are the regulatory subunits (R-subunits) of PKA where cAMP and the catalytic subunit compete for the same CBD. The R-subunits inhibit kinase activity, whereas cAMP releases that inhibition. Here, we use NMR to map at residue resolution the cAMP-dependent interaction network of the CBD-A domain of isoform Ialpha of the R-subunit of PKA. Based on H/D, H/H, and N(z) exchange data, we propose a molecular model for the allosteric regulation of PKA by cAMP. According to our model, cAMP binding causes long-range perturbations that propagate well beyond the immediate surroundings of the PBC and involve two key relay sites located at the C terminus of beta(2) (I163) and N terminus of beta(3) (D170). The I163 site functions as one of the key triggers of global unfolding, whereas the D170 locus acts as an electrostatic switch that mediates the communication between the PBC and the B-helix. Removal of cAMP not only disrupts the cap for the B' helix within the PBC, but also breaks the circuitry of cooperative interactions stemming from the PBC, thereby uncoupling the alpha- and beta-subdomains. The proposed model defines a signaling mechanism, conserved in every genome, where allosteric binding of a small ligand disrupts a large protein-protein interface.

Synthesis and activity of novel glutathione analogues containing an urethane backbone linkage

The new GSH analogues H-Glo(-Ser-Gly-OH)-OH (5), its O-benzyl derivative 4, and H-Glo(-Asp-Gly-OH)-OH (9), characterized by the replacement of central cysteine with either serine or aspartic acid, and containing an urethanic fragment as isosteric substitution of the scissile gamma-glutamylic junction, have been synthesized and characterized. Their ability to inhibit human GST P1-1 (hGST P1-1) in comparison with H-Glu(-Ser-Gly-OH)-OH and H-Glu(-Asp-Gly-OH)-OH, which are potent competitive inhibitors of rat GST 3-3 and 4-4, has been evaluated. In order to further investigate the effect of the isosteric substitution on the binding abilities of the new GSH analogues 4, 5 and 9, the previously reported cysteinyl-containing analogue H-Glo(-Cys-Gly-OH)-OH has been also evaluated as a co-substrate for hGSTP1-1.