Structure determination of [Arg8]vasopressin methylenedithioether in dimethylsulfoxide using NMR

Ligand-based peptide design and combinatorial peptide libraries to target G protein-coupled receptors

G protein-coupled receptors (GPCRs) are considered to represent the most promising drug targets; it has been repeatedly said that a large fraction of the currently marketed drugs elicit their actions by binding to GPCRs (with cited numbers varying from 30-50%). Closer scrutiny, however, shows that only a modest fraction of (≈60) GPCRs are, in fact, exploited as drug targets, only ≈20 of which are peptide-binding receptors. The vast majority of receptors in the humane genome have not yet been explored as sites of action for drugs. Given the drugability of this receptor class, it appears that opportunities for drug discovery abound. In addition, GPCRs provide for binding sites other than the ligand binding sites (referred to as the "orthosteric site"). These additional sites include (i) binding sites for ligands (referred to as "allosteric ligands") that modulate the affinity and efficacy of orthosteric ligands, (ii) the interaction surface that recruits G proteins and arrestins, (iii) the interaction sites of additional proteins (GIPs, GPCR interacting proteins that regulate G protein signaling or give rise to G protein-independent signals). These sites can also be targeted by peptides. Combinatorial and natural peptide libraries are therefore likely to play a major role in identifying new GPCR ligands at each of these sites. In particular the diverse natural peptide libraries such as the venom peptides from marine cone-snails and plant cyclotides have been established as a rich source of drug leads. High-throughput screening and combinatorial chemistry approaches allow for progressing from these starting points to potential drug candidates. This will be illustrated by focusing on the ligand-based drug design of oxytocin (OT) and vasopressin (AVP) receptor ligands using natural peptide leads as starting points.

Conformational solution studies of (Sar7)desamino- and (MeAla7)desamino-vasopressin analogues using NMR spectroscopy

Solution structures of two analogues of vasopressin with an amino acid sequence of c[Mpa1-Tyr2-Phe3-Gln4-Asn5-Cys6]-Xaa7-Arg8-Gly9-NH2 (Xaa = Sar [I] or MeAla [II]) were established using ROE and the 3J(HNH alpha) couplings. Each of the peptides was found to exist in two stable isomers, pertaining to the cis or trans status of the Cys6-Xaa7 peptide bond, thus giving rise to four study objects. Two methods for studies of the conformational properties of the structures were compared. In the first, the algorithm consisted of three steps: (i) An Electrostatically Driven Monte-Carlo (EDMC) search for low-energy conformations. (ii) Simulations of the NOESY spectra and the vicinal couplings for these conformations. (iii) Determination of the statistical weights of the conformations with the ANALYZE package, so as to meet the best fit of the averaged NOE intensities and couplings to the experimental data. In the second method, the distance constraints and the torsion angles were used as the usual constraints in the Distance Geometry and Simulated Annealing algorithms. The flexibility of the pressin ring and the C-terminus was characterized by a large number of families of conformations. The presence of the beta-turn at position 4,5 was confirmed for all low energy structures found. The use of the EDMC method for the elaboration of the NMR data for small flexible peptides yielded an adequate description of their conformational diversity and is the method of choice for the analysis of their solution structures.