Isolation and functional expression in Escherichia coli of a gene encoding phosphatidylethanolamine methyltransferase (EC 2.1.1.17) from Rhodobacter sphaeroides.
Phosphatidylcholine is a major component of membranes in most eukaryotes, but it is found only in a small number of bacteria, where it is synthesized by N-methylation of phosphatidylethanolamine. In yeast and other fungi the methylation of phosphatidylethanolamine to phosphatidylcholine proceeds in two steps: the methylation of phosphatidylethanolamine by phosphatidylethanolamine methyltransferase followed by the methylation of monomethylphosphatidylethanolamine by phospholipid methyltransferase. Here we describe the isolation of two allelic phosphatidylcholine-deficient mutants of Rhodobacter sphaeroides which are unable to methylate phosphatidylethanolamine, monomethylphosphatidylethanolamine, or dimethylphosphatidylethanolamine. A DNA fragment containing a gene designated pmtA, which encodes a 22.9-kDa protein, was found to complement both mutants. Expression of this gene in Escherichia coli, which normally lacks phosphatidylcholine or methylated derivatives of phosphatidylethanolamine, resulted in the formation of phosphatidylcholine. A protein extract derived from the E. coli strain expressing the pmtA gene was able to convert phosphatidylethanolamine, mono- and dimethylphosphatidylethanolamine into phosphatidylcholine. Based on these data we conclude that the product of the pmtA gene catalyzes a sequence of three chemically distinct, methylation reactions beginning with phosphatidylethanolamine and leading to the formation of phosphatidylcholine in R. sphaeroides.
Arondel
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V
Michigan State University, Department of Energy Plant Research Laboratory, East Lansing 48824-1312.
Benning
C
C
Somerville
C R
CR
D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D004269:DNA, Bacterial; D004926:Escherichia coli; D008780:Methyltransferases / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D050941:Phosphatidyl-N-Methylethanolamine N-Methyltransferase; D010713:Phosphatidylcholines / Q000096:biosynthesis; D050918:Phosphatidylethanolamine N-Methyltransferase; D012242:Rhodobacter sphaeroides / Q000201:enzymology* / Q000235:genetics
D004269:DNA, Bacterial; D010713:Phosphatidylcholines; D008780:Methyltransferases; D050918:Phosphatidylethanolamine N-Methyltransferase; D050941:Phosphatidyl-N-Methylethanolamine N-Methyltransferase