A novel lysophosphatidylethanolamine dehydrogenase from myxococcus xanthus
Avadhani, Madhavi Sitarama
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Myxococcus xanthus serves as a prokaryotic paradigm to study multicellularity in bacteria. Nutrient limitation initiates a developmental program in which the cells exhibit spatially and temporally regulated, morphologically distinct behaviors. The developmental program is coordinated by a series of intercellular signals. The most significant among them is the contact-dependent signal termed the C-signal which is absolutely essential for completion of development. The protein responsible for C-signaling, CsgA, belongs to the short-chain alcohol dehydrogenase (SCAD) family of enzymes. CsgA is proteolytically processed into a 17 kDa form. Much debate has focused on whether intercellular signaling occurs because of the enzymatic activity of the full length form or if the 17 kDa form is itself the signal. The genetic basis for the enzymatic role of CsgA comes from isolation of overexpression suppressor mutants. Overexpression of SocA, a SCAD with 28% identity to CsgA almost exclusively in the enzyme active site, not only suppresses the C-signaling defect, but also restores C-signaling to csgA mutants upon extracellular complementation. In addition, conserved residues of CsgA are shown to be essential for C-signaling. The potential role of SocA in generating the C-signal was exploited to determine the biochemical basis for C-signaling. We developed a dehydrogenase assay based screen coupled with mass spectrometry to identify SocA substrates. Our results indicate that SocA performs a novel biochemical reaction in oxidizing lysophoaphatidylethanolamine. Oxidized lysophosphatidylethanolamine does not function as an intercellular signal in M. xanthus.