Fig. 4: Furin activation loop.

a Activation of PLTs by furin. Proteins were incubated with (+) or without (−) furin for 1 h at 25 °C, and loaded onto an SDS-PAGE gel in a reducing buffer. Corresponding elements are labelled as described in (b). Variations in the fragment sizes follow the difference in the size of each PLT ranging from 66.6 to 73.0 kDa before cleavage (Supplementary Table 1 and Fig. 2). b Schematic of the PE structure showing the di-chain component resulting from furin cleavage. c Structure of PE (PDB 1IKQ; grey) with the conserved furin recognition site shown as sticks and scissile bond as a sphere. The loop (labelled ‘loop I’) with strong sequence variation within proximity of the furin cleavage site is indicated. Structures of d Collimonas (Cfx; blue), e Chromobacterium (Hmx; green), f Janthinobacterium (Jlx; red), and g Shewanella (Spx; yellow) exotoxins, labelled as per (c) with disordered Cfx region in (d) marked by a dashed line.