Biosynthesis of Enterobacterial Common Antigen in Esc~erichia coli
نویسنده
چکیده
Twelve independent TnlO insertion mutants of Escherichia coli K12 were isolated that were defective in the synthesis of enterobacterial common antigen (ECA). The mutants were identified by screening a random pool of TnlO insertion mutants for their ECA phenotype using a colony-immunoblot assay. All 12 of the TnlO insertion mutants were found to be located in the chromosomal region of the rff-rfe genes. Four of the TnlO insertions were in rfe genes while the remaining eight TnlO insertions were in rff genes. All of the rfe::TnlO insertion mutants were defective in the synthesis of GlcNAc-pyrophosphorylundecaprenol (CWPP-GIcNAc, lipid I), the first lipid-linked intermediate involved in ECA synthesis. Biochemical characterization of the rff::TnlO insertion mutants revealed that they were defective in various steps of ECA synthesis subsequent to the synthesis of lipid I. These defects included: (i) the inability to synthesize UDPManNAcA due to TnZO insertions in the structural genes for UDP-GlcNAc-2-epimerase (rffE) and UDPManNAcA (N-acetyl-D-mannosaminuronic acid) dehydrogenase (rffD), (ii) defects in the synthesis of CE5GlcNAc-ManNAcA (lipid II) due to insertion of transposon TnlO in the structural gene for the UDPManNAcA transferase (rffiW), (iii) the inability to synthesize TDP-Fuc4NAc (4-acetamido-4,6-dideoxy-Dgalactose) due to TnlO insertions in the structural gene for the transaminase that catalyzes the conversion of TDP-4-keto-6-deoxy-D-glucose to TDP-4-amino-4,6dideoxy-D-galactose (rffA), and (iv) defects in steps subsequent to the synthesis of CeB-GlcNAc-ManNAcAFuc4NAc (lipid III). In addition, a re-examination of a mutant possessing the rff-726 lesion revealed that it was defective in the synthesis of lipid III due to a defect in the structural gene for the Fuc4NAc transferase WV.
منابع مشابه
Staphylococcus aureus cap5O and cap5P genes functionally complement mutations affecting enterobacterial common-antigen biosynthesis in Escherichia coli.
The Staphylococcus aureus cap5P and cap5O genes of the type 5 capsule biosynthetic locus restore enterobacterial common-antigen expression to Escherichia coli mutants defective in rffE and rffD gene expression, respectively. Cap5P and Cap5O likely function as UDP-GlcNAc 2-epimerase and UDP-ManNAc dehydrogenase enzymes, respectively, in the synthesis of the capsule precursor UDP-ManNAcA.
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