Journal of Biotechnology 118 (2005) 406–412 Bacterial inclusion bodies are cytotoxic in vivo in absence of functional chaperones DnaK or GroEL Nuria Gonz´ alez-Montalb´ an, M. Mar Carri ´ o, Sergi Cuatrecasas, Anna Ar´ ıs, Antonio Villaverde ∗ Institut de Biotecnologia i de Biomedicina, Departament de Gen` etica i de Microbiologia, Universitat Aut` onoma de Barcelona, Bellaterra, 08193 Barcelona, Spain Received 13 January 2005; received in revised form 6 May 2005; accepted 12 May 2005 Abstract Cytotoxicity of cytoplasmic bacterial inclusion bodies has been explored in vivo in cells producing a model, misfolding-prone -galactosidase fusion protein. The formation of such aggregates does not result in detectable toxicity on Escherichia coli producing cells. However, a deficiency in the main chaperones DnaK or GroEL but not in other components of the heat shock system such as the chaperone ClpA or the protease Lon, promotes a dramatic inhibition of cell growth. The role of DnaK and GroEL in minimizing toxicity of in vivo protein aggregation is discussed in the context of the conformational stress and the protein quality control system. © 2005 Elsevier B.V. All rights reserved. Keywords: Aggregation; Chaperones; DnaK; E. coli; GroEL; Protein folding 1. Introduction Abnormal protein aggregation and its interference with cell physiology are matters of rising interest because of the increasing incidence of amyloid-linked pathologies. By experimentally approaching this issue, exogenously added aggregates have proved to be deleterious to cultured mammalian cells (Bucciantini et al., 2002), specially when occurring as fibril precur- ∗ Corresponding author. Tel.: +34 935812148; fax: +34 935812011. E-mail address: Antoni.Villaverde@uab.es (A. Villaverde). sor, amorphous aggregates. The organized clustering of misfolded protein as less toxic, true fibrils has been then regarded as a cell protective mechanism. Orga- nized protein packaging could prevent soluble cell pro- teins from harmful interaction with unusually exposed hydrophobic patches. Conformational inactivation of cell proteins by these contacts, or permeabilization of cell membranes by channel-like aggregates could be independent although not necessarily exclusive dele- terious mechanisms of protein aggregation (Olofsson et al., 2002; Stefani and Dobson, 2003). However, the detailed biology of aggregate-promoted toxicity remains still unsolved. 0168-1656/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jbiotec.2005.05.024