Inclusion bodies are insoluble aggregates that are formed by bacteria to store excess recombinant protein produced during expression. These are hard to separate during bioprocessing and can mean that up to 95 per cent of the protein expressed by the bacterial culture is unusable.
Now, a team of scientists led by chemist David Weliky of Michigan State University have identified a way of delving into the secondary structure of these inclusion bodies using nuclear magnetic resonance (NMR) spectroscopy.
That is important because production teams often try to break down inclusions in order to get at the trapped protein. This requires knowledge of the three-dimensional structure of the stored protein, so that once extracted it can be ‘refolded’ into the correct conformation to restore its desired activity.
Typically, the protein is separated from host cell contaminants such as endotoxin by lysing the bacterial biomass, and separating the inclusion body using centrifugation or other approaches such as tangential flow filtration or microfiltration.
By using NMR in combination with labelling of protein with radioactive isotopes, the researchers were able to establish that – at least in Escherichia coli cells making a recombinant influenza virus known as FHA2 - much of the protein within the inclusion bodies is correctly folded.
That means that it may be possible to extract the protein from the inclusion bodies without separating and refolding, according to Weliky. The work is published in the Journal of the American Chemical Society.
With the world protein therapeutics market tipped to rise from $63bn in 2007 to $87bn by 2010, according to Kalorama Information, there is a pressing need to boost manufacturing capacity and streamline the production of protein.
“This approach will be applicable to structural analysis of many inclusion body proteins and should provide useful information for optimising solubilisation and purification protocols of these proteins,” said the researchers.
J. Am. Chem. Soc., 2008, 130 (38), pp 12568–12569 http://pubs.acs.org/doi/abs/10.1021/ja8039426