Mytilus edulis hemolymph contains pro-opiomelanocortin: LPS and morphine stimulate differential processing

Mytilus edulis hemolymph contains mammalian-like proopiomelanocortin (POMC). The 20 kDa protein was purified by high pressure gel permeation chromatography, anti-adrenocorticotropin (ACTH)-affinity column and reverse-phase HPLC. The amino acid sequence determination was by Edman degradation, enzymatic treatments and Western blot analysis. Of the six peptides found in this opioid precursor, methionine-enkephalin, gamma-melanocyte stimulating hormone (MSH), alpha-MSH and ACTH exhibited 100, 80, 85 and 74% sequence identity, respectively, with the mammalian counterparts. beta-Endorphin and gamma-LPH exhibited only 25 and 10% sequence identity. Dibasic amino acid residues were found at the C-terminus of MSH and ACTH, indicating cleavage sites. The alpha-MSH is flanked at the C-terminus by Gly-Lys-Lys, representing an amidation signal. ACTH and CLIP (80% sequence identity) are also C-terminally flanked by dibasic amino acid residues. Furthermore, morphine, in a dose-dependent manner, increased the hemolymph levels of alpha-MSH and ACTH (1-39) in a naloxone and phosphoramidon antagonizable manner, indicating a neutral endopeptidase (24.11; NEP) mediated cleavage. Lipopolysaccharide (10 microg/animal) stimulated the processing of ACTH (1-39) yielding ACTH (1-24) in a cleavage that is independent of NEP, but dependent on aspartyl proteases, demonstrating differential enzymatic cleavage of ACTH (1-39). Taken together, POMC is present in invertebrates and its processing can be altered depending on the signal.