CONICET | Buscador de Institutos y Recursos Humanos

Sterol Carrier Protein-2 (SCP-2) is a nonspecific lipid transfer protein that has been implicated in the uptake, transfer, and metabolism of cholesterol, branched-chain fatty acids, acyl-CoA conjugates, and other lipids. SCP-2 module is present as a domain of multidomain proteins or as single domain polypeptides in all forms of life. SCP-2 structure and function has been studied mostly in mammals and next in insects. In these organisms, it has been generally found that the main function of this protein is related to the peroxysomal degradation of lipids. We have shown that the SCP-2 from the dimorphic yeast Yarrowia lipolytica, a model microorganism for studying hydrophobic substrates utilization, is a 128-amino-acid basic protein inducible by fatty acids(1). YLSCP-2 is located in the yeast peroxisomes and is able to bind and transfer a variety of lipids to membranes by a collision-mediated mechanism(2). Our results on YLSCP-2 X-ray diffraction showed the lipid binding site in the protein as a large system of interconnected tunnels and surface pockets partially occupied by palmitate(3). Despite having such detailed structural information, very little is known about SCP-2 function in plants, fungi and prokaryotes. Intriguingly, Saccharomyces cerevisiae and Schizosaccharomyces pombe are the only organisms known to lack SCP-2 or any related domain; they have also difficulties to adapt growing on lipids. For those reasons we overexpress YLSCP-2 in S. cerevisiae and Y. lipolytica in order to elucidate its function in vivo. Yeast cellular morphology and lipid bodies content were evaluated by observation of stained cells with the fluorescence dye Bodipy and by transmission electron microscopy. Total cellular fatty acids were determined by trans-esterification to methyl esters and gas chromatography. Although no differences were seen in growth for control and modified yeasts on glucose or oleic acid, we found that YLSCP-2 overexpressing cells grown on glucose are more sensitive to H2O2; conversely, YLSCP-2 cells grown on oleic acid restore H2O2 resistance. Particularly, under lipogenic conditions (glucose excess and nitrogen limitation) Y. lipolytica cells that constitutively overexpress YLSCP-2 decrease the level of lipid accumulation to lipid bodies, comparing to the parental strain where the protein is induced only under lipid feeding; besides we observe filamentation. Expectedly, under those conditions, a Y. lipolytica null mutant lacking YLSCP-2 improve resistance to H2O2 and better accumulate lipids, even more yet than in the parental strain. So, we hypothesize that during yeast cell lipogenesis SCP-2 may be involved in trafficking lipids and their reactive oxygen species derivatives generated by H2O2, like peroxidized lipids, delivering them through the cell.(1) Ferreyra et al. 2006. Arch. Biochem. Biophys. 453(2): 197-206.(2) Falomir et al.2009. Biophys. J. 97(1): 248-56.(3) Perez De Berti et al. 2013. J. Struct. & Func. Genomics. 14(4):145-53.