Characterization of Bacillus thuringiensis Cry1 class proteins in relation to their insecticidal action

Thirty nine Bt Cry1 subgroup protein sequences were retrieved from NCBI and analyzed for physicochemical properties, active site and relationship in relation to their variations in toxicity. Cry1 proteins were found to be hydrophilic and stable. SOSUI server predicted presence of two transmembrane regions in Ag and a single transmembrane region from Aa to Ae. EMBOSS PepWheel tool analysis of the transmembrane regions showed that there were 23 highly conserved residues towards the N terminal which are hydrophobic and more than half of the residues were neutrally charged. No signal peptide was detected which classifies the Cry1 group proteins as non-secretory proteins. Cry1 proteins have very high composition of neutral amino acids and might transform into negative charge after solubilization in alkaline environment (insect midgut). The negatively charged protein might misfold causing difficultly to digest and thereby be toxic to lepidopteran. Active sites of Cry1 proteins with more than 50% neutral amino acids showed wide insecticidal spectrum and further positive correlation (r = 0.7731) was observed between neutral amino acids and insect species affected (Y = -138.21 + 2.907X). Similarity of sequences was found between Cry1 proteins based on their high or low spectrum of insecticidal activity.