Fig. 2: Ca²⁺-dependent self-cleavage and activation.

a–c Electron densities for Ca²⁺-dependent self-cleavage and activation in crystals. The electron densities were drawn as gray isomeshes contoured at 1.3σ. The distances between the catalytic dyad (His86 and Cys139) and the cleavage site of Lys225 carbonyl carbon are 3.2 Å and are shown as red dashes. a Without Ca²⁺. b With 10 mM Ca²⁺. c With 10 mM Ca²⁺ by using microcrystals. d Schematics of major fragments produced in self-cleavage of AtMC4 and its cleavage of GST-fusion of substrate Propep1 (GST-Propep1). e Ca²⁺-dependent self-cleavage and activation of AtMC4. f Ca²⁺-dependent processing of GST-Propep1 by AtMC4. Here a R6A/R7A double mutant in Propep1 is used to highlight the Ca²⁺-dependent cleavage at the site of Arg69. Cleavage of the wild-type GST-Propep1 is shown in Supplementary Fig. 8e where higher concentration of Ca²⁺ cleaves Propep1 at an additional site of R6/R7.