Bacterial phosphatidylethanolamine biosynthesis through phosphatidylserine

A reusable two-reaction module for de novo phosphatidylethanolamine biosynthesis from CDP-diacylglycerol in bacteria. Phosphatidylserine synthase (PssA) transfers the phosphatidyl group of CDP-diacylglycerol to L-serine to form phosphatidylserine, and pyruvoyl-dependent phosphatidylserine decarboxylase (Psd) converts phosphatidylserine to phosphatidylethanolamine and CO2 at the cytoplasmic membrane. The first step is carried out by two unrelated enzyme architectures: a type-I, peripheral-membrane PssA of the phospholipase D superfamily, typical of gamma- and some beta-proteobacteria such as Escherichia coli, and a type-II, integral-membrane CDP-alcohol phosphatidyltransferase PssA, typical of Gram-positive bacteria such as Bacillus subtilis. Some genomes, such as Pseudomonas putida KT2440, encode both. The decarboxylation step is performed by a single conserved Psd family whose proenzyme self-cleaves to generate the pyruvoyl prosthetic group.

The module begins with CDP-diacylglycerol and L-serine and ends with phosphatidylethanolamine. CDP-diacylglycerol synthesis, phosphatidylglycerol and cardiolipin branches (bacterial_phosphatidylglycerol_cardiolipin_biosynthesis), lipid acyl-chain remodeling, and alternative phosphatidylethanolamine routes such as the Kennedy pathway are outside the boundary. The eukaryotic CHO1/PSD1/PSD2 implementation of the same two reactions is modeled in cdp_dag_phospholipid_synthesis, because its PS synthase steps are ER-localized and its decarboxylases mitochondrial or endomembrane; this module is therefore kept bacterial rather than generalized to all organisms. Psd autocatalytic maturation is required for activity but is a property of the terminal enzyme rather than a separate pathway reaction. Bacterial phosphatidylserine synthases occur in mechanistically distinct type-I and type-II architectures; these type names follow the PssA nomenclature of PMID:39693441. UniProt's CDP-alcohol phosphatidyltransferase class-I/class-II family labels describe a different classification axis and appear inverted relative to the PssA type names. PANTHER family groundings: type-I PssA sits in PTHR12586:SF1, the only subfamily of PTHR12586, whose official name refers to mitochondrial PGS1 because the subfamily also contains eukaryotic PGP synthases; the PAINT node PTN001758495 restricts the annoton to the phosphatidylserine-synthase clade. Type-II PssA sits in PTHR14269:SF61 (P. putida PP_4677, also yeast CHO1) and PTHR14269:SF59 (B. subtilis PssA). Bacterial Psd sits mainly in PTHR10067:SF6 (with eukaryotic PSD1) and partly in SF17. The PTHR12586, PTHR14269 and PTHR10067 family reviews adjudicate these scopes.