Genomics, Structure and Function of Oleosins from 140 Organisms

Triacylglycerols (TAGs) are the major molecules of energy storage in eukaryotes. TAGs accumulate in oil bodies/oil droplets in plants and animals. Oleosins (OLEs) are a group of mostly low-molecular-mass hydrophobic proteins localized on the surfaces of plant oil droplets.  OLEs/oils ratio determines the size and shape of intracellular oil bodies, but the precise function of OLEs is uncertain. The objectives of this study were to identify OLEs from diverse species, to perform genome-wide analysis of OLEs, to classify OLEs, to identify conserved sequence motifs and amino acid residues in OLEs , OLE subfamilies and OLEs within individual species. Data mining identified 1640 OLE accessions from more than 140 organisms in the NCBI databases. More than 1400 OLE accessions from 105 plant species were selected for subsequent analysis. There were lots of redundancies of OLE accessions in the databases. For example, Arabidopsis thaliana had 17 OLEs but had 149 accessions in the NCBI databases. All but a few exceptions contained the perfect “proline knot” motif (PX5SPX3P). These OLEs were hydrophobic proteins with > 40% hydrophobic amino acid residues. They had similar properties and amino acid composition. Genome-wide phylogenetic analysis and multiple sequence alignment demonstrated that these proteins were separated into 5 OLE subfamilies. There were distinct patterns of sequence conservation among the OLE subfamilies and within individual species. These analyses should facilitate studying the structure-function relationship and identify critical amino acid residues in OLE for metabolic engineering of TAGs.