[N-palmitoylated peptide 232-245 of rat type 4 melanocortin receptor possessing agonistic activity]

Melanocortin receptors of the type 4 (M4R) play a key role in the regulation of feeding behavior, neuroendocrine functions, and energy metabolism. The alterations in their functional activity induce obesity, metabolic syndrome, depression, and mental disorders, which makes the search of selective regulators of M4R to be one of the actual problems of molecular endocrinology. Promising for the development of such regulators is to design peptides corresponding to functionally important regions of M4R. The purpose of this study was to study the influence of synthesized N-palmitoylated peptide Palm-Thr-Gly-Thr-Ile-Arg-Gln-Gly-Ala-Asn-(Nle)-Lys-Gly-Ala-Ile232-245-amide (Palm-232-245) structurally corresponding to the C-terminal half of the third intracellular loop (ICL-3) of rat M4R on functional activity of adenylyl cyclase signaling system (ACSS) in the fractions of synaptosomal membranes isolated from the brains of male rats. It has been shown that, at a concentration of 10(-7) M and higher, Palm-232-245 stimulates the basal activity of adenylyl cyclase (AC) in the synaptosomal membranes and increases the basal level of GTP binding with the EC50 values of 71 and 267 nM, respectively. Under the combined action of low concentrations of the peptide (10(-7)-10(-6) M) and M4R agonists, α-melanocyte-stimulating hormone (α-MSH) and THIQ (10(-7) M), we observed an additivi stimulatory effect on AC, which disappeared when the peptide concentration was increased to 10(-4)-10(-3) M. In the synaptosomal membranes preincubated with 10(-5) M peptide, the maximum stimulatory effect of M4R agonists on AC activity was lower than that in controls, and EC50 values for this effect, on the contrary, increased. In the case of combined action of the peptide and hormones (γ-MSH, serotonin, PACAP-38) that activate AC via the other receptors, the additivity of their stimulating effects on the ACSS persisted throughout the range of peptide concentrations. The effect of the peptide was not observed in myocardial and testicular membranes no in which there is M4R homologous to the peptide. Thus, N-palmitoylated peptide Palm-232-245 specifically activates the ACSS in the rat brain by acting as intracellular M4R agonist. This may be used to create drugs regulating brain melanocortin system and physiological processes that depend on it.