4.3. Engineering the yeast membrane for membrane protein production
The yeast membrane differs in composition from that of mammalian membranes. This is likely to be highly relevant to subsequent structural and functional studies of recombinant membrane proteins produced in yeast because lipids have a particularly important role in the normal function of membrane proteins; they contribute to membrane fluidity and may directly interact with membrane proteins.
In an attempt to “humanize” the yeast membrane, yeast strains have been developed that synthesize cholesterol rather than the native yeast sterol, ergosterol. This was achieved by replacing the ERG5 and ERG6 genes of the ergosterol biosynthetic pathway with the mammalian genes DHRC24 and DHRC7 [59], [60] and [61], respectively. The gene products of DHRC7 and DHRC24 were identified as key enzymes that saturate sterol intermediates at positions C7 and C24 in cholesterol (but not ergosterol) synthesis ( Fig. 4). Erg5p introduces a double bond at position C22 and Erg6p adds a methyl group at position C24 in the ergosterol biosynthetic pathway and therefore competes with the gene product of DHRC24 for its substrate.