In 3.8 M urea solution, BoNT/A LC loses most of its α-helices which convert into random coil, while the β-sheets remain intact and the tertiary structure is preserved.
In 5M urea solution, BoNT/A LC molecule regains α-helicity, yet, loses some β-sheets, and the tertiary structure changes significantly.
In 7M urea solution, BoNT/A LC unfolds completely and loses almost all its tertiary structure elements, while retaining only residual secondary structure content (α-helices).
In Confocal scan image of DR BoNT/A internalization in M17-TR2 neuroblastoma cells pre-incubated with 200 nM DR BoNT/A for 48 h.(a) Panel A. Hoechst 33342 Nucleus dye (cyan color), Panel B. Alexa fluor 594 membrane dye (red color), Panel C Alexa fluor 488 labeled DR BoNT/A (green color), Panel D. Co-localization image of all three dyes. Hoechst 33342, Alexa fluor 594, and Alexa fluor 488 was excited at excitation wavelength of 392, 594, and 488 nm respectively.