Protein aggregation as bacterial inclusion bodies is reversible

Inclusion bodies are refractile, intracellular protein aggregates usually o bserved in bacteria upon targeted gene overexpression, Since their occurren ce has a major economical impact in protein production bio-processes, in vi tro refolding strategies are under continuous exploration. In this work, we prove spontaneous in vivo release of both beta -galactosidase and P22 tail spike polypeptides from inclusion bodies resulting in their almost complete disintegration and in the concomitant appearance of soluble, properly fold ed native proteins with full biological activity. Since, in particular, the tailspike protein exhibits an unusually slow and complex folding pathway i nvolving deep interdigitation of beta -sheet structures, its in vivo refold ing indicates that bacterial inclusion body proteins are not collapsed into an irreversible unfolded state. Then, inclusion bodies can be observed as transient deposits of folding-prone polypeptides, resulting from an unbalan ced equilibrium between in vivo protein precipitation and refolding that ca n be actively displaced by arresting protein synthesis. The observation tha t the formation of big inclusion bodies is reversible in vivo can be also r elevant in the context of amyloid diseases, in which deposition of importan t amounts of aggregated protein initiates the pathogenic process. (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.