The effect of N-terminal extension on the structure and function of human interleukin-1 beta

Interleukin-1 beta (IL-1 beta) and N-terminally extended Met-Glu-Ala-Glu-IL-1 beta (MEAE-IL-1 beta) were cloned and expressed in E. coli. Extension of the chain results in a limited conformational change reflected by the CD spectrum in the far ultraviolet, while the aromatic side chains responsible for the CD in the near ultraviolet are not affected. No difference in immunoreactivity between IL-1 beta and MEAE-IL-1 beta is observed in the IL-1 beta ELISA. Like IL-1 beta, MEAE-IL-1 beta exhibits biological activity tested in the costimulatory mouse thymocyte (LAF) assay. The specific biological activity of IL-1 beta is 3 x 10(8) U/mg and that of MEAE-IL-1 beta 3 x 10(6) U/mg. Like IL-1 beta, MEAE-IL-1 beta displaces [125I]IL-1 beta from mouse thymocytes and the binding affinities of the two forms differ by a factor of 10(2). Finally the inhibitory effect of the two IL-1 beta forms on in vitro insulin secretion from isolated rat islets of Langerhans was measured. Again MEAE-IL-1 beta is 10(2) times less potent than IL-1 beta. The structure-activity relationship for IL-1 beta and MEAE-IL-1 beta is discussed.