Cellular import of synthetic peptide using a cell-permeable sequence in plant protoplasts

In this paper, we describe a rapid method to incorporate biologically active synthetic peptide in plant protoplasts. The peptides used contain a hydrophobic membrane permeable sequence as a carrier for the import through the plasma membrane. The membrane permeable sequence corresponds to the h-region, the more hydrophobic domain found in the signal peptide of secreted proteins. To evaluate the feasibility of the method, we synthesized a cell-permeable peptide with an h-region of a plant signal peptide plus residues 410–419 of the human c-myc oncogene product. Detection was performed via fluorescence analysis using specific monoclonal anti-c-myc primary antibody and FITC-conjugated secondary antibody. No saturation of import was observed, suggesting that the mechanisms involved do not require energy. The half-life time of the internalized peptide was estimated and results indicate that peptide concentration into protoplasts was constant for 8 h following incorporation. This method is complementary to microinjection or to the use of membrane permeabilizing reagents to study in vivo protein–protein or DNA–protein interactions. Finally, this method was used to analyse a putative interaction between the conserved cytoplasmic tail of a transmembrane receptor (HaELP, Helianthus annuus EGF receptor like protein) and the cytoskeleton. No interaction was found between these components.