Análisis de fosforilación de la región SSIV-CR de almidón sintasa IV- en Arabidopsis thaliana

Abstract

Starch synthase (SSIV) plays a specific role in starch synthesis. Previous evidence in our laboratory has shown that SSIV forms dimers, which depends on a region located between the extended coiled-coil region and the glucosyltransferase domain of SSIV. This region is highly conserved between all SSIV enzymes sequenced to date. In this work, we have analyzed the potential phosphorylation of two amino acid residues of the protein (tyrosine 515 and serine 459) and its possible role in the dimerization and activity of SSIV. We have obtained mutated versions of the AtSSIV polypeptide where the amino acid Tyr 515 has been changed to Phe or Glu residue and Ser 459 has been changed to Ala or Asp. We show that the phosphorylation of the Tyr 515 would prevent the formation of a dimer and hence the interaction with FBN1b and suggest that the change of the Tyr 515 residue by a Phe does not affect to the formation of a dimer but reduces the enzymatic activity of the protein considerably. A similar decrease was observed when the amino acid was changed to a Glu residue, suggesting that Tyr 515 residue is necessary for the AtSSIV activity.