SECONDARY STRUCTURE OF THE ENTOMOCIDAL TOXIN FROM BACILLUS-THURINGIENSIS SUBSP KURSTAKI HD-73

The secondary structure of the toxin from Bacillus thuringiensis subsp. kurstaki (Btk) HD-73 was estimated by Raman, infrared, and circular dichroism spectroscopy, and by predictive methods. Circular dichroism and infrared spectroscopy gave an estimate of 33-40% α-helix, whereas Raman and predictive methods gave approximately 20%. Raman and circular dichroism spectra, as well as predictive methods, indicated that the toxin contains 32-40% β-sheet structure, whereas infrared spectroscopy gave a slightly lower estimate. Thus, all of these approaches are in agreement that the native conformation of Btk HD-73 toxin is highly folded and contains considerable amounts of both α-helical and β-sheet structures. No significant differences were detected in the secondary structure of the toxin either in solution or as a hydrated pellet. © 1990 Plenum Publishing Corporation.