Nativelike secondary structure in interleukin-1 beta inclusion bodies by attenuated total reflectance FTIR

Attenuated total reflectance FTIR has been used to study the structure of human interleukin-1 beta in inclusion bodies (IBs) and other aggregated forms. The secondary structure composition of native wild-type IL-1 beta determined by FTIR is in excellent agreement with that previously determined by crystallography and NMR: 52% beta-sheet, 25% loop/irregular structure, and 23% turn. Remarkably, IL-1 beta inclusion bodies exhibit secondary structural composition very similar to that of the native protein. The results indicate that the IBs form from a folding intermediate that has nativelike secondary structure. The secondary structure content of aggregated IL-1 beta, formed either in refolding or by thermal denaturation, was identical within experimental error to that of the IB, indicating that these aggregates were formed from intermediates with structures similar to that of the inclusion body.