Investigating the effects of membrane curvature inducing proteins on lipid droplets in Saccharomyces cerevisiae.

BACKGROUND: Reticulons (Rtn1p, Rtn2p) and Yop1p are proteins shaping the endoplasmic reticulum (ER) membrane curvature their function being to a large degree responsible for molding the membrane curvature in the tubular ER area. Lipid biosynthesis mainly takes place in the tubular parts of the ER and lipid droplets are formed in the tubular ER membrane. Nucleation constitutes the rate-limiting step in lipid droplet formation and is modulated by membrane curvature; specifically increasing membrane curvature lowers the activation energy required for lipid lens nucleation. The aim of this work was to investigate the effects, modifying the ER membrane curvature would have on lipid droplets in Saccharomyces cerevisiae. METHODS AND RESULTS: We created and screened strains overexpressing different combinations of the membrane curvature inducing genes RTN1, RTN2 and YOP1 and additionally the gene inducing ER membrane expansion, DGK1, in four different genetic strain backgrounds. We examined the strains by microscopy and quantified lipid composition by gas chromatography-mass spectrometry. We found that overexpressing membrane curvature inducing proteins decreases the size of the lipid droplets. A reduction in lipid droplet size was accompanied by an apparent increase in their number. We observed that the change in cell size seemed to be partially connected to the strain background. We also noticed altered lipid composition which was linked to the strain backgrounds. CONCLUSIONS: Overexpression of curvature inducing proteins affected lipid droplet size and number, presumably by affecting nucleation. However, the morphological changes of lipid droplets were not accompanied by increased lipid production. Our findings provide a basis for future research on how ER structure modifications influence the lipid droplet dynamics in S. cerevisiae.