Membranes oil bodies

Oleosins are a class of seed proteins associated with oil-body membranes in developing and mature embryos. As a simple purification procedure, foreign peptides have been routinely fused with oleosin for the production of foreign proteins in plant seeds. Oleosin fusion facilitates protein purification via cleavage of the fusion protein by an endonuclease, followed by a flotation centrifugation procedure in which the oleosin fusion protein floats to the surface with the oil bodies, thus removing recombinant protein along with the oil-body fraction. 

Herman, E.M. Inmunogold-localization and synthesis of an oil-body membrane protein in developing soybean seeds. Planta 1987,172, 336-345. 

Loer, D.S. and Herman, E.M. (1993) Cotranslational integration of soybean Glycine max) oil body membrane protein oleosin into microsomal membranes. Plant Physiol. 101, 993-998. 

Kalinski, A., Loer, D.S., Weisemann, J.M., Matthews, B.F. and Herman, E.M. (1991) Isoforms of soybean seed oil body membrane protein. Plant Mol. Biol. 17, 1095-1098. Kater, M.M., Koningstein, G.M., Nijkamp, J.J. and Stuitje, A.R. (1991) cDNA cloning and expression of Brassica napus enoyl-acyl carrier protein reductase in Escherichia coli. Plant Mol. Biol. 17, 895-909. 

Murphy, D.J., Cummins, I. and Kang, A.S. (1989) Synthesis of the major oil-body membrane protein in developing rapeseed (Brassica napus) embryos. Integration with storage-lipid and storage-protein synthesis and implications for the mechanism of oil-body formation. Biochem. J. 258, 285-293. 

Connected with the controversial views on the origin of the oil bodies is the question as to whether they are bounded by membranes. Evidence for and against the existence of some kind of peripheral membrane is presented in Section 3.3.8. We should note, in addition, favourable evidence for an oil body membrane raised by the freeze-fracture studies on barley aleurone cells [20 b] and by biochemical analyses of peanut and walnut oil bodies which reveal phospholipid and protein characteristic of membranes. Finally, we should be aware that in addition to the possible existence of membrane protein, enzyme protein may also occur in oil bodies. Enzymes for fatty acid biosynthesis have been reported in oil bodies of developing castor bean [35] and for triglyceride hydrolysis (acid lipases) in the mature endosperm of this species the latter enzymes may not occur in oil bodies of other species (Chap. 6). 

Fig.2 Immunogold labelled sections of cells from maturing cotyledons of (A) rapeseed (B) mustard (C) radish. Sections were treated with IgG raised against the rapeseed 19kDa "olein . Note specific labelling of the oil-body membranes of all three oilseed species. No gold labelling was observed in control sections treated with pre-immune serum.

Soybean tissue is composed of many cells containing oil, protein and metabolites, which supply energy, nitrogen storage reserves, and other important compounds, respectively, to support the germination of new plants. The triglycerides are stored in discrete bodies called oil bodies or spherozomes. The preponderance of the protein is storage protein, which is concentrated in other discrete bodies known as protein bodies. Most of the phospholipids are associated with membranes around the protein bod-... 

TAG produced through acyltransferase action accumulates as droplets between the leaflets of the ER. Oil bodies surrounded by a half-unit membrane and ranging in size from 0.2 to 2 micrometers eventually bud off the surface of the ER. 

The lipolytic process in germinating oil seeds is still unclear. How seed oils, present in oil bodies, are converted to products which can then be handled by the fatty acid oxidation system of glyoxysomes, is not clear. It appears that membrane-bound lipases are involved in the process. A further area for clarification is the intracellular transport of insoluble triacylglycerols from oil bodies to the site of complete (or partial) hydrolysis and thence to the glyoxysomal enzymes of gluconeogenesis. Recent electron microscope studies with several oil seeds have provided evidence for a close association of ribosome-containing membranes with spherosomes these may be lipolytic membranes involved in triacylglycerol breakdown (Wanner and Theimer, 1978). 

The oil bodies of castor seeds lack a peripheral membrane, but within the organelles are vacuolelike inclusions, 0.1-0.3 ju.m in diameter, that stain... 

The oil bodies of C. abyssinica synthesized fatty acids from [ Cjmalonyl-CoA and triacylglycerols from [ C]palmitoyl-CoA or [ C]glycerol-3-P (Gurr et al., 1974). Evidence that this was not due to contamination was, first, that the fat fraction synthesized a pattern of fatty acids (predominantly erucic acid) totally different from that of other subcellular fractions and, second, that of all the fractions tested only the fat fraction had an appreciable specific activity for triacylglycerol biosynthesis. In ultrastructural studies, no inclusions could be seen in Crambe oil bodies, and it was concluded that the enzymes were contained in a bounding membrane or in granular material that was always associated with the oil body fraction (Fig. 12). 

Thus oil bodies are not simply inert storage organelles for reserve lipid but contain the enzymatic apparatus for the biosynthesis of their own oil. Whether this synthesis occurs in granular inclusions within the oil bodies, in a boundary membrane, or in associated granular material remains to be substantiated by further research. Recent studies on wax synthesis in developing jojoba seed (Simmodsin chimensis) have also shown that the fat fraction contains all the enzymes for the synthesis of wax from malonyl-CoA (Stumpf, this volume. Chapter 7, Section I,C,3). 

The hydrophobic stretch of 72 residues in the oleosin is the longest one foimd in all prokaryotic and eukaryotic proteins. The mechanism by which it has evolved is intriguing. A postulation can be made partly based on the length of 72 residues being roughly 4 times that of a transmembrane polypeptide and on the occurrence of several relatively hydrophilic residues at the center of the stretch. Initially, a short hydrophilic polypeptide joining two transmembrane hydrophobic polypeptides, of possibly an ER membrane protein, became hydrophobic through DNA sequence mutation. A continuous hydrophobic stretch resulted, which consisted of about half of the final 72 residues. This primitive hydrophobic stretch could stabilize an oil body,... 

Figure 1. Electron micrographs of oil bodies of Illinois High Oils (IHO) and Illinois Low Oils (ILO). Inside the embryonic scutellar cells upper and middle panels), oil bodies of IHO lefi) were substantially larger and generally spherical, whereas those of ILO right) were smaller and more heterogeneous in size with irregularly contoured surfaces. Note that the mitochondria with well-recognized double membranes were of a similar size in both IHO and ILO. In isolated preparations lower panels), the oil bodies of IHO left) and ILO right) resembled those...

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