Structural Properties of Bacterial Inclusion Bodies

The overexpression of a recombinant protein in bacteria often leads to its deposition in cytoplasmic or periplasmic aggregates, called inclusion bodies (IBs). The polypeptide newly synthetized by the ribosome reaches its native conformation through folding intermediates that can be more prone to aggregation compared to the native form. IBs might contain proteolytic fragments of the recombinant protein, ribosomal components, and traces of phospholipids and nucleic acids, as well as a small fraction of polypeptides unrelated to the target protein. The relationship between the retention of residual native-like structure and IB formation was also investigated by Fourier transform infrared (FTIR) in the case of two recombinant E. coli strains expressing different levels of human interferon-alpha-2b. This chapter gives a brief overview of the main experimental methods applied to IB structural characterization: fluorescence spectroscopy and microscopy, flow cytometry, circular dichroism, FTIR spectroscopy, electron microscopies, atomic force microscopy, and x-ray fiber diffraction.