Fig. 8.

Left bottom panel: TH8–9 hydrophobic hairpin with highlighted histidine residues. Top panel: A single replacement of H322 results in repositioning of the TH5 helix from TM state (WT, black) to IF state (H322Q mutant, red), associated with loss of channel activity [Rodnin et al., 2011; Vargas-Uribe, Rodnin, Kienker, et al., 2013]. This repositioning can be followed by changes in spectral position of W281 (lower insert) and it’s quenching with brominated lipids (upper insert). Right bottom panel: Summary of the relative cellular toxicity in various mutants of diphtheria toxin and relative OCS activity of the T-domain with the same mutations in planar bilayers [Ladokhin, Vargas-Uribe, Rodnin, Ghatak, & Sharma, 2017]. The Activity Ratio (AR) between the two activities significantly deviates from one for the mutants with C-terminal histidine substitutions, indicating that channel activity is not required for the cytotoxicity associated with the translocation of the catalytic domain. Reprinted by permission from Kyrychenko, A., Posokhov, Y.O., Vargas-Uribe, M., Ghatak, C., Rodnin, M.V., Ladokhin, A.S., Fluorescence applications for structural and thermodynamic studies of membrane protein insertion, in: C.D. Geddes (Ed.), Reviews in fluorescence 2016, Springer 2017, pp. 243–274; COPYRIGHT 2017 from Springer.