Fine architecture of bacterial inclusion bodies

The molecular organisation of protein aggregates, formed under physiologica l conditions, has been explored by in vitro trypsin treatment and electron microscopy analysis of bacterially produced inclusion bodies (IBs), The kin etic modelling of protein digestion has revealed variable proteolysis rates during protease exposure that are not compatible with a surface-restricted erosion of body particles but with a hyper-surfaced disintegration by sele ctive enzymatic attack. In addition, differently resistant species of the I B proteins coexist within the particles, with half-lives that differ among them up to 50-fold. During in vivo protein incorporation throughout IB grow th, a progressive increase of proteolytic resistance in all these species i s observed, indicative of folding transitions and dynamic reorganisations o f the body structure. Both the heterogeneity of the folding state and the t ime-dependent folding transitions undergone by the aggregated polypeptides indicate that IBs are not mere deposits of collapsed, inert molecules but p lastic reservoirs of misfolded proteins that would allow, at least up to a certain extent, their in vivo recovery and transference to the soluble cell fraction. (C) 2000 Federation of European Biochemical Societies.