Calmodulin-like protein AtCML3 mediates dimerization of peroxisomal processing protease AtDEG15 and contributes to normal peroxisome metabolism

Matrix enzymes are imported into peroxisomes and glyoxysomes, a subclass of peroxisomes involved in lipid mobilization. Two peroxisomal targeting signals (PTS), the C-terminal PTS1 and the N-terminal PTS2, mediate the translocation of proteins into the organelle. PTS2 processing upon import is conserved in higher eukaryotes, and in watermelon the glyoxysomal processing protease (GPP) was shown to catalyse PTS2 processing. GPP and its ortholog, the peroxisomal DEG protease from Arabidopsis thaliana (AtDEG15), belong to the Deg/HtrA family of ATP-independent serine proteases with Escherichia coli DegP as their prototype. GPP existes in monomeric and dimeric forms. Their equilibrium is shifted towards the monomer upon Ca(2+)-removal and towards the dimer upon Ca(2+)-addition, which is accompanied by a change in substrate specificity from a general protease (monomer) to the specific cleavage of the PTS2 (dimer). We describe the Ca(2+)/calmodulin (CaM) mediated dimerization of AtDEG15. Dimerization is mediated by the CaM-like protein AtCML3 as shown by yeast two and three hybrid analyses. The binding of AtCML3 occurs within the first 25 N-terminal amino acids of AtDEG15, a domain containing a predicted CaM-binding motif. Biochemical...Continue Reading