• aspartic proteinases;
  • C2 domain;
  • cardosin A;
  • phospholipase D;
  • RGD/KGE sequences

Cardosin A is an RGD-containing aspartic proteinase from the stigmatic papillae of Cynara cardunculus L. A putative cardosin A-binding protein has previously been isolated from pollen suggesting its potential involvement in pollen–pistil interaction [Faro C, Ramalho-Santos M, Vieira M, Mendes A, Simões I, Andrade R, Verissimo P, Lin X, Tang J & Pires E (1999) J Biol Chem274, 28724–28729]. Here we report the identification of phospholipase Dα as a cardosin A-binding protein. The interaction was confirmed by coimmunoprecipitation studies and pull-down assays. To investigate the structural and molecular determinants involved in the interaction, pull-down assays with cardosin A and various glutathione S-transferase-fused phospholipase Dα constructs were performed. Results revealed that the C2 domain of phospholipase Dα contains the cardosin A-binding activity. Further assays with mutated recombinant forms of cardosin A showed that the RGD motif as well as the unprecedented KGE motif, which is structurally and charge-wise very similar to RGD, are indispensable for the interaction. Taken together our results indicate that the C2 domain of plant phospholipase Dα can act as a cardosin A-binding domain and suggest that plant C2 domains may have an additional role as RGD/KGE-recognition domains.