Bacterial Inclusion Body

Bacterial Inclusion Body (IB)

·        Inclusion body (IBs) are partially folded protein aggregate. When level of expression of protein goes beyond 2% of the total cellular proteins it leads to formation of inclusion body. It contains mostly single type   polypeptides and very little amount of host protein components, DNA and RNA fragments.

·       IBs are found in cytoplasm, if secretion signal used it can produces in periplasm also.

·       IBs are formed due to overexpression of heterologous protein, which are unable to solubilize in  cytoplasm and form aggregates.      

·       Bacterial cytoplasm having reduced environment hence di-sulfide bonds of proteins are not formed and proteins remain unfolded/partial folded.   

·       Protein in IBs have native like secondary structure. Proteins in IBs are aggregated by ionic and hydrophobic interaction.

·        IBs reflect light so it can be visualized by phase contrast microscopy.

·         Diameter of IBs varies from 0.5 to 1.3 µm.

In E.Coli IBs are deposited at poles only, this polar localization result in partition of inclusion bodies in an asymmetric way between the daughter cells.

            Advantages of IBs

·         High level of expression  >30% of cellular protein

·         Easy of isolation

·         Resistance to proteolytic attack

·         Homogeneity in protein

·         Less contamination

·         Reduce purification step

·         Lower or less degradation

            Disadvantages of IBs

·         Protein recovery from aggregate is challenging step

·         Protein having multiple di-sulfide bond requires more elaborate refolding process.