FIGURE 1.

The mammalian PMCH gene, PMCH protein, and the peptides of the MCH family. (A) The mammalian PMCH gene is composed of three exons and two introns. Both introns and exons have variable lengths, with the sizes depicted in this diagram corresponding to human PMCH. The transcribed product of PMCH is formed by five components: a signal peptide (sp), encoded in Exon 1; a structural chain, formed by both Exons 1 and 2; two MCH gene-related peptides (MGRPs), neuropeptide G-E (NGE) and neuropeptide E-I (NEI), both encoded in Exon 2; and a mature melanin-concentrating hormone (MCH), with 3 N-terminal residues found in Exon 2, a residue formed by Exon 2 and Exon 3 combining to generate its codon, and 15 C-terminal residues found in Exon 3. Both MCH and NEI can be generated through dibasic proteolytic sites, indicated in the diagram by RR and KR, and NGE may be cleaved at a single basic site K. Neuropeptide E-I contains an amidation site in its C-terminal portion, indicated by G. (B) Structure of the peptides generated from PMCH. Both NGE and NEI are linear peptides characterized by a predominance of negatively charged residues. The precise structure of NGE is unknown, given that this peptide has never been isolated and characterized. Mature MCH, on the other hand, is a cyclic peptide, due to a cysteine bridge formed between residues 7 and 16. The ring structure formed between the two cysteine residues, indicated by black circles, is essential for the binding activity of MCH to its receptors. Residue 17 plays an important role in potentiating MCH binding (indicated by the letter P). Adapted with permission from Bittencourt and Diniz (2018).