Question

The genetically engineered proteins that accumulate in bacterial inclusion bodies form amyloid structures. Such proteins are often difficult to recover in functional form from the bacteria. Explain.

Answer 1

The inclusion bodies are tiny particles found freely suspended and floating within the cytoplasmic matrix.Formation of inclusion bodies in bacterial hosts poses a major challenge for large scale recovery of bioactive proteins. The process of obtaining bioactive protein from inclusion bodies is labor intensive and the yields of recombinant protein are often low.Formation of inclusion bodies occurs as a result of intracellular accumulation of partially folded expressed proteins which aggregate through non-covalent hydrophobic or ionic interactions or a combination of both.Aggregates of recombinant proteins occur as small supramolec-
ular entities in the soluble cell fraction or as larger protein clusters that precipitate as insoluble materials. Therefore,the recombinant protein species range along a spectrum of conformational versions that embrace soluble protein species,soluble aggregates and insoluble aggregates .Soluble aggregates or
proto-aggregates have been usually considered as precursors of large protein deposits. Aggregates tend to eventually accumulate in recombinant cells
as refractile (under optical microscope visualisation), electro-dense (under transmission electron microscope visualisation)submicron particles known as inclusion bodies .

Inclusion bodies are formed during high-level recombinant protein production, and formation of inclusion bodies is a major concern in biotechnology. Despite of the distinctive morphological difference, bacterial inclusion bodies have been found to have some amyloid-like properties, suggesting that they might contain structures similar to amyloid-like fibrils.

Bacterial inclusion bodies are submicron protein clusters usually found in recombinant bacteria that have been traditionally considered as undesirable products from protein production processes. However, being fully biocompatible, they have been recently characterized as nanoparticulate inert materials useful as scaffolds for tissue engineering, with potentially wider applicability in biomedicine and material sciences. Current protocols for inclusion body isolation from Escherichia coli usually offer between 95 to 99% of protein recovery, what in practical terms, might imply extensive bacterial cell contamination, not compatible with the use of inclusion bodies in biological interfaces.