Dermaseptin S9 (Drs S9), GLRSKIWLWVLLMIWQESNKFKKM, isolated from frog skin, does not resemble any of the cationic and amphipathic antimicrobial peptides identified to date, having a highly hydrophobic core sequence flanked at either side by cationic termini. Previous studies [Lequin O, Ladram A, Chabbert A, Bruston F, Convert O, Vanhoye D, Chassaing G, Nicolas P & Amiche M (2006) Biochemistry45, 468–480] demonstrated that this peptide adopted a non‐amphipathic α‐helical conformation in trifluoroethanol/water mixtures, but was highly aggregated in aqueous solutions and in the presence of sodium dodecyl sulfate micelles. Circular dichroism, FTIR and attenuated total reflectance FTIR spectroscopies, combined with a surface plasmon resonance study, show that Drs S9 forms stable and ordered β‐sheet aggregates in aqueous buffers or when bound to anionic or zwitterionic phospholipid vesicles. These structures slowly assembled into amyloid‐like fibrils in aqueous environments via spherical intermediates, as revealed by electron microscopy and Congo red staining. Drs S9 induced the directional migration of neutrophils, T lymphocytes and monocytes. Interestingly, the antimicrobial and chemotactic activities of Drs S9 are modulated by its amyloid‐like properties. Whereas spherical oligomers of Drs S9 exhibit antimicrobial activity, the soluble, weakly self‐associated forms of Drs S9 act on human leukocytes to promote chemotaxis and/or immunological response activation in the same range of concentration as amyloidogenic peptides Aβ(1–42), the most fibrillogenic isoform of amyloid beta peptides, and the prion peptide PrP(106–126).

CC chemokine receptor type 2 (CCR2) is a key molecule in inflammatory diseases and is an obvious drug target for the treatment of inflammation. A number of nonpeptidic, competitive CCR2 antagonists have been developed, but none has yet been approved for clinical use. Our aim was to identify a short peptide that showed allosteric antagonism against human and mouse CCR2. On the basis of sequence analysis and 3‐dimensional modeling, we identified an original 7‐ d ‐amino acid peptidic CCR2 inhibitor that we have called extracellular loop 1 inverso (ECL1i), d(LGTFLKC). In vitro , ECL1i selectively and potently inhibits CC chemokine ligand type 2 (CCL2)‐triggered chemotaxis (IC ₅₀ , 2 μM) but no other conventional CCL2‐associated events. We used the classic competitive CCR2 antagonist, BMS22 {2‐[(isopropylaminocarbonyl)amino]‐ N ‐[2‐[[cis‐2‐[[4‐(methylthio)benzoyl] amino]cyclohexyl]amino]‐2‐oxoethyl]‐5‐(trifluoromethyl)benzamide}, as positive control and inhibited CCL2‐dependent chemotaxis with an IC ₅₀ of 18 nM. As negative control, we used a peptide with the same composition as ECL1i, but in a different sequence, d(FKLTLCG). In vivo , ECL1i (4 mg/kg) interfered with CCR2‐positive cell recruitment and attenuated disease progression in experimental autoimmune encephalomyelitis, a mouse model of multiple sclerosis. This study establishes ECL1i as the first allosteric inhibitor of CCR2 with functional selectivity. ECL1i is a promising new agent in therapeutic development, and it may, by its selective effect, increase our understanding of CCR2 signaling pathways and functions.—Auvynet, C., Baudesson de Chanville, C., Hermand, P., Dorgham, K., Piesse, C., Pouchy, C., Carlier, L., Poupel, L., Barthélémy, S., Felouzis, V., Lacombe, C., Sagan, S., Chemtob, S., Quiniou, C., Salomon, B., Deterre, P., Sennlaub, F., Combadière, C. ECL1i, d(LGTFLKC), a novel, small peptide that specifically inhibits CCL2‐dependent migration. FASEB J. 30, 2370–2381 (2016). www.fasebj.org