The topology of the ER-resident phospholipid methyltransferase Opi3 of Saccharomyces cerevisiae is consistent with in trans catalysis (original) (raw)

Journal of Biological Chemistry

Abstract

Phospholipid N-methyltransferases (PLMTs) synthesize phosphatidylcholine (PC) by methylating phosphatidylethanolamine using S-adenosylmethionine (SAM) as a methyl donor. Eukaryotic PLMTs are integral membrane enzymes located in the endoplasmic reticulum (ER). Recently Opi3, a PLMT of the yeast Saccharomyces cerevisiae was proposed to perform in trans catalysis, i.e. while localized in the ER Opi3 would methylate lipid substrates located in the plasma membrane at membrane contact sites. Here, we tested whether the Opi3 active site is located at the cytosolic side of the ER membrane, which is a prerequisite for in trans catalysis. The membrane topology of Opi3 (and its human counterpart, phosphatidylethanolamine N-methyltransferase [PEMT], expressed in yeast) was addressed by topology prediction algorithms and by the substituted cysteine accessibility method (SCAM). The results of these analyses indicated that Opi3 (as well as PEMT) has an N-out C-in topology and contains four transme...

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