Function
While LL-37 acts as a broad-spectrum antimicrobial and immunomodulatory peptide involved in host defense and wound repair, but can also promote inflammation and cancer cell proliferation in some contexts5215, Melanotan I is approved in some regions for prevention of phototoxicity in erythropoietic protoporphyria and is studied as a skin-darkening, photoprotective peptide3444.
Mechanism
While LL-37 works as a cationic amphipathic 37-amino-acid cathelicidin peptide generated from hCAP18 that disrupts microbial membranes and modulates innate immunity, including chemotaxis, cytokine induction, and NET formation521586, Melanotan I is a linear 13-amino-acid analog of α-MSH (afamelanotide) that selectively activates MC1R on melanocytes, increasing eumelanin synthesis and providing photoprotection3444.
Length and Sequence
LL-37 is 37 amino acids long, whereas Melanotan I is shorter as it has a length of 13 amino acids. LL-37 is made up of a sequence of Leucine, Leucine, Glycine, Aspartic acid, Phenylalanine, Phenylalanine, Arginine, Lysine, Serine, Lysine, Glutamic acid, Lysine, Isoleucine, Glycine, Lysine, Glutamic acid, Phenylalanine, Lysine, Arginine, Isoleucine, Valine, Glutamine, Arginine, Isoleucine, Lysine, Aspartic acid, Phenylalanine, Leucine, Arginine, Asparagine, Leucine, Valine, Proline, Arginine, Threonine, Glutamic acid, Serine. Melanotan I is made up of a sequence of Serine, Tyrosine, Serine, Nle, Glutamic acid, Histidine, Phenylalanine, Arginine, Tryptophan, Glycine, Lysine, Proline, Valine.