Endomorphins have been proposed as the endogenous ligand agonists of the μ-opioid receptor; however, no propeptide precursor protein for endomorphins has been identified. Here, to identify the presumed precursor of endomorphins, we designed an immunoscreening assay using specific affinity-purified rabbit antisera raised against synthetic endomorphins in a whole mouse brain cDNA library. Following this approach, we identify a DNA sequence encoding a protein precursor, which we name proMexneurin, that contains three different peptide sequences: Mexneurin-1 (an endomorphin-like peptide), Mexneurin-2, and Mexneurin-3, a peptide which appears to be unrelated to endomorphins. RT-PCR analysis and in situ hybridization reveal a widespread distribution of proMexneurin mRNA throughout the mouse brain. Both Mexneurin-1 and Mexneurin-3 peptides display biological activities in the mouse CNS.

Matus-ortega ME, Leff gelman P, Calva-nieves JC, et al. FEBS Lett. 2017;