The Green Gut: Chlorophyll Degradation in the Gut of Spodoptera littoralis
P252, a 252-kDa Bombyx mori protein located on the larval midgut membrane, has been shown to bind strongly with Bacillus thuringiensis Cry1A toxins (Hossain et al. Appl Environ Microbiol 70:4604–4612, 2004). P252 was also shown to bind chlorophyllide (Chlide) to form red fluorescence–emitting complex Bm252RFP with significant antimicrobial activity (Pandian et al. Appl Environ Microbiol 74:1324–1331, 2008). In this article, we show that Cry1A toxin bound with Bm252RFP and Bm252RFP–Cry1A macrocomplex, with both antimicrobial and insecticidal activities, was formed. The insecticidal activity of Bm252RFP–Cry1Ab was reduced from an LD50 of 1.62 to 5.05 μg, but Bm252RFP–Cry1Aa and Bm252RFP–Cry1Ac did not show such reduction. On the other hand, the antimicrobial activity of Bm252RFP–Cry1Ab was shown to retain almost the same activity as Bm252RFP, while the other two complexes lost around 30% activity. The intensity of photo absorbance and fluorescence emission of Bm252RFP–Cry1Ab were significantly reduced compared to those of the other two complexes. Circular dichroism showed that the contents of Cry1Ab α-helix was significantly decreased in Bm252RFP–Cry1Ab but not in the other two toxins. These data suggested that the reduction of contents of α-helix in Cry1Ab affected the insecticidal activity of the macrocomplex but did not alter the antimicrobial moiety in the macrocomplex of Bm252RFP–Cry1Ab.