Immunological and biochemical characterization of the major seed oil-body membrane proteins

Abstract

The major seed oil-body membrane proteins have been purified from a range of plant species by preparative SDS/PAGE, The purified proteins were used to elicit antibodies in rabbits and mice. Antisera were obtained from the following major oil-body membrane proteins; a) From mice (M), anti-Brassica napus 19kDa serum ( Mnapl9 ), anti-Brassica napus native oil-body proteins serum ( Mnap native ),anti-mustard 20kDa serum ( Mmus20 ), anti-radish 20kDaserum (Mrad20), anti-Crambe 20kDa serum ( Mcra20 ), anti-sunflower 20kDa serum( Msun20 ), anti-sunflower 19kDa serum ( Msunl9kDa ), anti-safflower 20kDaserum (Msaf20) and anti-soybean 24kDa serum ( Msoy24 ), b) From rabbit (R),anti-Brassica napus 19kDa ( Rnap 19 ), anti-mustard 20kDa serum ( Rmus20 ),anti-sunflower 20kDa serum ( Rsun20 ) and anti-soybean 24kDa ( Rsoy24 ), The cross-reactivity of each of these antibodies with oil-body proteins from species other than those to which they were raised was investigated by immunoblotting and ELISA. Considerable cross-reactivity was found, mostly within the Cruciferae, Compositae, and Legurainosae families, Cross-reactivity was also found between plant families and even between genera. There was also extensive cross-reaction between certain monocotyledonous species of Graminae( Zea mays and Triticum durum ) with dicotyledonous species of the Cruciferae, Compositae and Leguminosae, The oil-body specific nature of the antibodies and their cross-reactivities were confirmed by immunogold labelling studies. The total amino acid compositions of two of the purified oil-body membrane proteins, i.e., the Brassica napus 19kDa and radish 20kDa proteins, were determined. Many similarities were observed in the amino acid compositions of these two proteins with those of the only other published plant species, i.e. the maize 15.5kDa and soybean 24kDa oil-body proteins. Similarities were also observed with the amino acid composition of the animal apolipoprotein Bl00 and bovin milk fat globule membrane proteins. These similarities included a moderately hydrophobic character and high levels of Glu and Leu, The immunological cross-reactivities and compositional similarities of these plant oil-body proteins imply that they may belong to a family of membrane proteins which share both structural and functional attributes. These plant proteins may also be related to animal lipoproteins which share the common function of enclosing oil-bodies, whether in blood serum, milk, adipose cells, egg-yolk or oilseeds.