Solution structure and dynamics of a serpin reactive site loop using interleukin 1beta as a presentation scaffold

Human interleukin-1beta (IL1beta) was used as a presentation scaffold for the characterization of the reactive site loop (RSL) of the serpin alpha1-antitrypsin (A1AT), the physiological inhibitor of leukocyte elastase. A chimeric protein was generated by replacement of residues 50-53 of IL1beta, corresponding to an exposed reverse turn in IL1beta, with the 10-residue P5-P5' sequence EAIPMSIPPE from A1AT. The chimera (antitrypsin-interleukin, AT-IL) inhibits elastase specifically and also binds the IL1beta receptor. Multinuclear NMR characterization of AT-IL established that, with the exception of the inserted sequence, the structure of the IL1beta scaffold is preserved in the chimera. The structure of the inserted RSL was analyzed relative to that of the isolated 10-residue RSL peptide, which was shown to be essentially disordered in solution. The chimeric RSL was also found to be solvent exposed and conformationally mobile in comparison with the IL1beta scaffold, and there was no evidence of persisting interactions with the scaffold outside of the N- and C-terminal linkages. However, AT-IL exhibits sigificant differences in chemical shift and NOE patterns relative to the isolated RSL that are consistent with local features of non-random structure. The proximity of these features to the P1-P1' residues suggests that they may be responsible for the inhibitory activity of the chimera.