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|Feature type||ORF, Verified|
Description of YGR157W: Phosphatidylethanolamine methyltransferase (PEMT), catalyzes the first step in the conversion of phosphatidylethanolamine to phosphatidylcholine during the methylation pathway of phosphatidylcholine biosynthesis
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== Cho2 - domain structure and involvement in autophagy via Atg8p / LC3 ==
Wlodarski et al (2011) (www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0023168) have identified a CoCoa_N domain at the carboxy-terminus of Cho2p. This is interesting, but not precisely for the reasons stated by Wlodarski et al., as explained below. Point (1) refers to the domain structure of Cho2p and points (2) and (3) provide an alternative likely function (and hence alternative binding partner) for a conserved motif in the carboxy-terminus of Cho2p to that suggested by Wlodarski et al.
(1) The enzymatic domain of Cho2p is repeated, as residues 35-321 are homologous to 344-577. This means that the whole amino-terminus 1-577 most likely contains an even number of transmembrane domains, despite automated prediction programmes suggesting an overall odd number. This is important because it sugests that the carboxy-terminus is in the cytoplasm (not in the lumen as might be assumed from Wlodarski et al.)
(2) the C-terminus of Cho2p contains WIGL. This motif is not only found in CoCoa_N, but also is found in the SKICH domains of phosphatidylinositol (4,5) bisphosphate 5-phosphatase (PIPP) and other proteins (Ooms et al. (2006) MBoC 17, 607-22).
Critically the motif is of the form WxxL, which is the minimal requirement for motifs binding to Atg8/LC3 (Noda et al. (2010) FEBS Letters 584:1379–85). WxxL motifs tend to have two other features also found in Cho2p: (A) they form beta-sheets, which is the structure for this portion of Cho2p predicted by PSI-PRED 3.0 (B) they are flanked by acidic residues (here in Cho2p: DDwiglYKVID). Together these factors create the strong suggestion that WIGL near the carboxy-terminus of Cho2p binds to Atg8p/LC3. Hence, it is predicted that Cho2p is directly involved in autophagy, possibly by methylating phosphatidylethanolamine, which is specifically required to activate Atg8p/LC3.
(3) Wlodarski et al. suggest that DWIGLYKV in Cho2p interacts with transcriptional activators related to p300, and so Cho2p is active in chromatic remodelling. However, there is little evidence to support this. Yang et al. (2006, Mol Endocrinol. 20: 3251-62) showed that the motif in CoCoa_N that binds to p300 is FLNVARTY, not DWIGLYKV which is >20 aa away. Also, Cho2p has no conserved sequence motif similar to FLNVARTY.
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- Kodaki T and Yamashita S (1987) Yeast phosphatidylethanolamine methylation pathway. Cloning and characterization of two distinct methyltransferase genes. J Biol Chem 262(32):15428-35 SGD PMID 2445736
- Paltauf F, et al. (1992) Regulation and compartmentalization of lipid synthesis in yeast. Pp. 415-500 in The Molecular and Cellular Biology of the Yeast Saccharomyces: Gene Expression, edited by Jones EW, Pringle JR and Broach JR. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press SGD PMID
- Summers EF, et al. (1988) Saccharomyces cerevisiae cho2 mutants are deficient in phospholipid methylation and cross-pathway regulation of inositol synthesis. Genetics 120(4):909-22 SGD PMID 3066687
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