Molecular modeling of the endogenous peptide Leu-Ser-Ala-Leu, pindolol, 5-hydroxytryptamine and their interactions...

Molecular modeling techniques were used to build a three-dimensional model of the human 5-HT1B receptor. The receptor model was used to examine receptor interactions of 5-hydroxytryptamine (serotonin), (S)pindolol and of the tetrapeptide Leu-Ser-Ala-Leu (LSAL), which recently has been shown to interact specifically with the 5-HT1B receptor. We have assumed that the NH3(+)-LSAL-COO- form of the tetrapeptide is the biologically active, and propose that a negatively charged residue conserved among various species homologues of the 5-HT1B receptor may act as a counter-ion for the positively charged N-terminus of the tetrapeptide. The strongest LSAL-receptor interactions were obtained after molecular dynamics simulations that were started with the N-terminus of LSAL positioned close to Asp352 in transmembrane helix 7. The model suggests that Asp352 in transmembrane helix 7 may act as a counter-ion for the positively charged N-terminus, and that the side chains of Tyr109 (transmembrane helix 2) and Trp125 (transmembrane helix 3) may form hydrogen bonds with the negatively charged C-terminus of LSAL.