The study shows that everyday substances like anti‑inflammatory pills, some food colorings, and bile‑related molecules can stick to the immune peptide LL‑37 and make it fold into a helix shape, which changes how it works in the body. This effect happens even in normal gut conditions and involves the peptide’s Lys8‑Arg19 region.

The human antimicrobial and immunomodulatory peptide LL-37 is ubiquitously expressed and secreted by epithelial cells of mucosal surfaces including the gastrointestinal tract, the primary absorption site of orally administered drugs and food components. Besides antimicrobial properties, LL-37 also contributes to the pathophysiology of various diseases such as ulcerative colitis, Crohn's disease and cancer. Non-covalent association of antiinflammatory drugs, porphyrin pigments, bile salts and food dyes to the peptide was uncovered and evaluated by circular dichroism (CD) spectroscopy. These agents induce the disorder-to-order conformational transition of the natively unstructured LL-37 leading to its helical folding. Even in the presence of chloride ions, when LL-37 is partially folded, the inducers were able to rise the α-helix content. CD titration data indicated positive cooperativity between the ligand molecules accommodated to the peptide chain resulting in multimeric complexes with apparent dissociation constants ranged from 2 to 500 μM. Computational docking suggested the prominent role of the Lys8-Arg19 segment in the accommodation of small molecules, governed principally by salt bridges and H-bonding. Since pleiotropic biological functions of LL-37 are strongly conformation-dependent, it could be anticipated that folding inducer compounds may modulate its in vivo actions and also of related cationic peptides.