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Amino-Terminus of Oleosin Protein Defines the Size of Oil Bodies - Topological Model of Oleosin-Oil Body Complex

Wahlroos T, Soukka J, Denesyuk A and Susi P

Lipids formed in seeds of oilseed plant are stored in specific cytosolic structures called oil bodies, which are covered with oleosin proteins. Disruption of oleosin layer by heat treatment makes lipids susceptible to oxidation. By analyzing the amino acid sequence of Arabidopsis oleosin, unique domains were identified within the aminoterminus of the protein. Removal of these domains affected both the size of oil bodies and their susceptibility to lipid-specific stain, Nile Blue A. Amino-terminally truncated oleosin mutant, which was in fusion to green fluorescent protein (GFP), confined to rough endoplasmic reticulum (rER) suggesting that the amino-terminus of oleosin is required for the efficient lateral transportation of oleosin proteins from rER to oil bodies. The size of oil bodies covered by amino-terminal mutants was at least 5 times larger than native oil bodies. Based on the observations, a topological model was generated, which could explain how oleosin maintains and protects the integrity of oil bodies during seed storage.