Contribution

The P20 helper protein is a 20 kDa protein that was first identified in 1987 by Mclean and Whiteley and following this discovery, it was hypothesized that this protein allows for the crystalization of Cyt1Aa, Cry4Ba, Cry11Aa, and Cry4Aa. Manasherob et al. (2001), later reported that plasmid constructs expressing only Cyt1Aa showed reduced colony-forming ability and Cyt1Aa protein expression (Manasherob et al., 2001). While Cyt1Aa and P20 expressing plasmid constructs showed higher Cyt1Aa protein expression and cell viability in recombinant E.coli cells (Manasherob et al., 2001). This confirms that P20 stabilizes Cyt1Aa and inhibits cell death. Although the exact mechanism by which P20 does this was not known in 1987, Manasherob et al. (2001) proposed that pre-mature activation of Cyt1Aa and lethality was a result of incomplete degradation of this Cyt protein. P20 binds to and prevents the degradation of Cyt1Aa, which ultimately results in the viability of the cell (E.coli and Bacillus thuringiensis cells) (Manasherob et al., 2001). This is an important step in the expression of Cyt1Aa because this Cyt protein does not form inclusion bodies that further protect the cell from Cyt1Aa’s cytotoxic effects (Manasherob et al., 2001). For these reasons, the coexpression of P20 must be considered when expression of Cyt1Aa is desired as this protein stabilizes the crystal formation and protects cells from the lethal effects of this protein.