title: Binding sites for human interferon-gamma in protocerebrum and hemolymph of tobacco hornworm (Manduca sexta) larvae differ in sensitivity to polycationic peptides.
abstract: We have recently characterized specific binding sites for human interferon-gamma on particulates prepared from the protocerebrum and hemolymph of tobacco hornworm larvae, Manduca sexta ¿(Parker, M.S., Ourth, D.D., 1999. Comp. Biochem. Physiol. B 122, 155-163). The sensitivity to sulfated polysaccharides indicated an involvement of oligobasic epitopes of hIFN-gamma in the binding. In the present study, we found that polycationic peptides inhibited the binding of [125I]hIFN-gamma to particulates from either the hemolymph or the protocerebrum of Manduca sexta larvae. With amino acid homopolymers, the rank order of potency was poly-L-lysine > poly-L-arginine >> poly-L-ornithine, while the acidic side chain polymer poly-L-aspartate was not inhibitory. However, the potency of all polycationic peptides was at least three-fold greater at the hemolymph particulates. Also, acidic polysaccharides such as heparin were much more efficacious in the inhibition of hIFN-gamma binding to hemolymph relative to protocerebral particulates. The peptide polycations inhibited the binding of [125I](Leu31,Pro34)human peptide YY, a ligand selective for the Y1 subtype of the neuropeptide Y receptor, to rabbit kidney or to parietal cortex particulates with the expected rank order of poly-L-arginine > poly-L-lysine >> poly-L-ornithine, and with little cross-tissue difference in affinity. The selectivity observed with M. sexta particulates indicates a preferential involvement of oligobasic lysine-rich C-terminal sequences of IFN-gamma, while large insect tissue-related affinity differences point to involvement of diverse oligoacidic sequences in binding to protocerebrum and hemolymph sites. This study provides evidence for the presence of molecules in lepidopteran larvae that are similar in structure to vertebrate co-receptors of IFN-gamma, and adds to the characterization of these binding sites.
authors.affiliation: Department of Microbiology and Molecular Cell Sciences, University of Memphis, TN 38152, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Parker
authors.forename: D D
authors.initials: DD
authors.lastname: Ourth
mesh_terms: D000596:Amino Acids / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive; D001923:Brain Chemistry; D006458:Hemolymph / Q000737:chemistry*; D006801:Humans; D007371:Interferon-gamma / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007700:Kinetics; D007814:Larva / Q000737:chemistry / Q000378:metabolism; D018402:Manduca / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011817:Rabbits; D011869:Radioligand Assay; D017476:Receptors, Neuropeptide Y / Q000378:metabolism; D014020:Tissue Extracts
chemical_list: D000596:Amino Acids; D017476:Receptors, Neuropeptide Y; D014020:Tissue Extracts; D007371:Interferon-gamma