4 9-KDA PROTEINS EXCRETED BY SOMATIC EMBRYOS OF GRAPEVINE ARE ISOFORMS OF LIPID-TRANSFER PROTEINS

Four 9-kDa small extracellular proteins produced by embryogenic cultur es in the absence of auxin have been purified from the extracellular m edium of grapevine somatic embryo cultures through cation-exchange chr omatography and hydrophobic-interaction chromatography. The partial am ino-acid sequences reflect high similarities between the four proteins as well as with the sequences established for carrot, spinach, millet and maize nonspecific lipid-transfer proteins. All these sequences sh ow conservation of three cysteines at positions 4, 14 and 30-32, as we ll as glycine, valine, tyrosine and lysine residues at positions 5, 7, 17 and 37, respectively. In-vitro lipid-transfer assays reveal that t he four proteins catalyze the transfer of phosphatidylcholine from lip osomes towards motochondria with an efficiency similar or higher than that of a purified maize lipid-transfer protein.