Peptide leucine arginine, a potent immunomodulatory peptide isolated and structurally characterized from the skin of the Northern Leopard frog, Rana pipiens

On the basis of histamine release from rat peritoneal mast cells, an octadecapeptide was isolated from the skin extract of the Northern Leopard frog (Rana pipiens), This peptide was purified to homogeneity using reversed-phase high performance liquid chromatography and found to have the following primary structure by Edman degradation and pyridylethylation: LVRGCWTKSYPPKPCFVR, in which Cys(5) and Cys(15) are disulfide bridged. The peptide was named peptide leucine-arginine (pLR), reflecting the N- and C-terminal residues. Molecular modeling predicted that pLR possessed a rigid tertiary loop structure with flexible end regions, pLR was synthesized and elicited rapid, noncytolytic histamine release that had a a-fold greater potency when compared with one of the most active histamine-liberating peptides, namely melittin, pLR was able to permeabilize negatively charged unilamellar lipid vesicles but not neutral vesicles, a finding that was consistent with its nonhemolytic action, pLR inhibited the early development of granulocyte macrophage colonies from bone marrow stem cells but did not induce apoptosis of the end stage granulocytes, i,e. mature neutrophils, pLR therefore displays biological activity with both granulopoietic progenitor cells and mast cells and thus represents a novel bioactive peptide from frog skin.

Inhibition and fibril formation and toxicity of a fragment of alpha-synuclein by an N-methylated peptide analogue

Alpha-synuclein has been linked to amyloidogenesis in Parkinson's disease and other neurodegenerative disorders. We have previously shown that a peptide comprising residues 68-78 of alpha-synuclein is the minimum fragment that, like alpha-synuclein itself, forms amyloid fibrils and exhibits toxicity towards cells in culture. Hughes et al. [J. Biol. Chem. 275 (2000) 25109] showed that an N-methylated derivative of Abeta(25-35) inhibited the formation of fibrils by Abeta(25-35) and reduced its toxicity. We have now extended this concept to an amyloidogenic alpha-synuclein-based peptide. Alpha-synuclein(68-78), N-methylated at G1y73, was compared to non-methylated peptide. Whereas alpha-synuclein(68-78) formed fibrils and was toxic to cells, the N-methylated analogue had neither of these properties. Moreover, an equimolar mixture of the non-methylated and methylated peptides formed very few fibrils and toxicity was markedly reduced.