Exposing cryptic antibacterial activity in Cyt1Ca from Bacillus thuringiensis israelensis by genetic manipulations

In an attempt to endow Cyt1Ca with Cyt1Aa-like antibacterial activity, both derived from Bacillus thuringiensis subsp. israelensis, two amino acids were replaced, E117V and N125A, so as to raise the hydrophobicity of the corresponding region, considered to be the membrane-active motif. The clones obtained included multiple repeats of VIEVLKSLLGIALA, corresponding to head-to-tail polymerization of the primer, translated in frame with Cyt1Ca. These versions of Cyt1Ca caused instant arrest in biomass growth and decreased viability upon expression in Escherichia coli. Multiple insertions of the non-mutated motif VIEELKSLLGINLA into the polypeptide were also lethal. To expose toxicity of the latter motif in the original Cyt1Ca, cyt1Ca was appropriately truncated.