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Two E.coli ArnC Homologues in Francisella novicida and their Functions in Lipid A Modification
Author(s) -
Song Feng,
Guan Ziqiang,
Raetz Christian R. H.
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.6.lb7-d
Subject(s) - chemistry , biochemistry , membrane , mutant , phosphate , gene
Two F. novicida homologues of E. coli ArnC synthesize substrates required for lipid A glycosylation at 1‐ and 6′‐positions. ArnC1 selectively condenses undecaprenyl phosphate and UDP‐glucose to form undecaprenyl phosphate‐glucose; ArnC2 catalyzes the condensation of undecaprenyl phosphate and UDP‐N‐acetylgalactosamine, instead of UDP‐galactosamine, to form undecaprenyl phosphate‐N‐acetylgalactosamine. The ArnC1 knockout of F. novicida produces only one free lipid A species, which is modified with a galactosamine residue at the 1‐position. The ArnC2 knockout makes two free lipid A species, the major form of which is not glycosylated at either the 1‐ or the 6′‐positions, and the minor form of which contains glucose at the 6′‐position. Membranes of the ArnC1 mutant cannot catalyze formation of undecaprenyl phosphate glucose, while membranes of the ArnC2 knockout catalyze this reaction with similar efficiency as wild‐type. Membranes of the ArnC2 knockout cannot generate undecaprenyl phosphate‐N‐acetylgalactosamine, while membranes of the ArnC1 knockout and the wild‐type do so at similar rates. We conclude that ArnC1 generates the immediate donor substrate for the modification of F. novicida lipid A with glucose, while ArnC2 makes a precursor of the actual donor substrate for modification of F. novicida lipid A with galactosamine. Supported by NIH grant R37‐GM51796 to CRHR.