Abstract
Hemopressin is a naturally occurring nonapeptide derived from the α-chain of hemoglobin that acts as an inverse agonist for the type-1 cannabinoid (CB1) receptor. Based on its in vivo activity, hemopressin is considered to have potential therapeutic applications in hypertension, pain, and obesity. We tested the hemopressin peptide for CB1 receptor agonist and antagonist activity in cAMP and β-arrestin recruitment assay and found it to be inactive. The lack of reproducibility of CB1 receptor antagonist/ inverse agonist activity of hemopressin has been attributed to formation of aggregates. Hemopressin was previously reported to convert into amyloid-like fibrils under aqueous conditions. However, the amino acid residues that modulate the aggregation propensity of hemopressin are not known. We have synthesized 25 different analogs of hemopressin and analyzed their aggregation properties using the principle of dynamic light scattering. We identified four conservative changes in the peptide sequence (Val2→DVal2, Asn3→Gln3, Leu7→Npg7, and C-OH→C-NH2) that lower the aggregation propensity of hemopressin. The results indicate that hemopressin aggregation is cooperative in nature and involves contribution from multiple amino acids within the peptide chain. The analogs are being evaluated for their functional activity in CB1 receptor assays. The structure-function studies of hemopressin would further help understand its aggregation property and explore its potential therapeutic applications.