CONFORMATION OF A T-CELL STIMULATING PEPTIDE OF INTERLEUKIN-1-BETA PROTEIN - CIRCULAR-DICHROISM STUDIES

A T-cell stimulating peptide Val-Gln-Gly-Glu-Glu-Ser-Asn-Asp-Lys-OH, t he 163-171 fragment epitope of interleukin-1 beta (IL-1 beta), has bee n synthesized in solution phase and purified by reverse-phase high-per formance liquid chromatography (RP-HPLC). The backbone conformation of the synthetic fragment, investigated in aqueous solution by circular dichroism (CD) spectroscopy, is qualitatively a mixture of beta-turns and random coil. Quantification of the CD spectra revealed the presenc e of a 9% beta-turn traction in water at pH 7.0, suggesting the occurr ence of the conformation for the epitope fragment in aqueous solution necessary for T-cell stimulation and antigenicity. Concomitant changes in CD spectra were observed with increases in the trifluoroethanol (T FE) concentration in water, and the beta-turn fraction in peptide incr eased to 28% at a concentration of 90% TFE. This helicogenic solvent, as well as other solvents such as methanol, acetonitrile and dioxane ( all favouring an ordered structure in peptides), failed to induce any alpha-helical conformation in the IL-1 beta (163-171) fragment, and CD spectra were attributed to only beta-turn ordered structure. This bet a-turn structure has also been found to be a theoretically preferred c onformation using Chou-Fasman proclivity data and is in accordance wit h the presence of an all-beta-globular conformation for its parent mol ecule IL-1 beta. Thus, the beta-turn conformation is probably involved in retention of T-cell stimulation activity in this synthetic epitope .