Systematic study of substance P analogs. II. Rapid screening of 512 substance P stereoisomers for binding to NK1 receptor.

Recent developments in multiple peptide synthesis have made it feasible to synthesize and screen large numbers of peptide analogs simultaneously. We report here a model study of large scale screening of stereoisomers of substance P with systematic D-amino acid replacements. Such studies are useful in exploring conformational requirements of peptide-receptor interaction and to provide empirical information for peptide drug design. 512 stereoisomers of SP were prepared by the multipin peptide synthesis method. Receptor binding affinities of these analogs were estimated by an iterative competition assay. Results obtained form a comprehensive database on the stereochemical requirement of SP binding to central NK1 receptor. Data from analogs with single D-amino acid replacement are consistent with those previously reported showing that SP binding is highly sensitive to the chirality change of the C-terminal residues (Gln6-Leu10), but less sensitive to the chirality change of the N-terminal residues (Arg1-Gln5). A qualitative analysis of the database by comparison of series of peptide pairs revealed a repeated pattern of affinity change with D-amino acid replacement, suggesting a largely additive binding activity of SP from each residue. On the other hand, possible intramolecular interactions between some N-terminal and C-terminal residues to form an optimal binding conformation were also found. A set of 189 peptides with IC50 values less than 5 microM was subjected to an empirical QSAR analysis using a linear additive model. The relative contribution coefficients obtained agreed with the observation that the predominant contribution comes from the C-terminal residues, suggesting considerable independency of each residue on binding to NK1 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)