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J. Bacteriol., 01 1998, 330-337, Vol 180, No. 2
GD Dotson, IA Kaltashov, RJ Cotter and CR Raetz
UDP-N-acetylglucosamine-3-O-acyltransferase (UDP-GlcNAc acyltransferase)
catalyzes the first step of lipid A biosynthesis (M. S. Anderson and C. R.
H. Raetz, J. Biol. Chem. 262:5159-5169, 1987). We here report the isolation
of the lpxA gene of Pseudomonas aeruginosa from a library of Pseudomonas
strain PAO1 expressed in Escherichia coli LE392 (J. Lightfoot and J. S.
Lam, J. Bacteriol. 173:5624-5630, 1991). Pseudomonas lpxA encodes a
10-carbon-specific UDP-GlcNAc acyltransferase, whereas the E. coli
transferase is selective for a 14- carbon acyl chain. Recombinant cosmid
1137 enabled production of a 3- hydroxydecanoyl-specific UDP-GlcNAc
acyltransferase in E. coli. It was identified by assaying lysozyme-EDTA
lysates of individual members of the library with 3-hydroxydecanoyl-acyl
carrier protein (ACP) as the substrate. Cosmid 1137 contained a 20-kb
insert of P. aeruginosa DNA. The lpxA gene region was localized to a 1.3-kb
SalI-PstI fragment. Sequencing revealed that it contains one complete open
reading frame (777 bp) encoding a new lpxA homolog. The predicted
Pseudomonas LpxA is 258 amino acids long and contains 21 complete
hexapeptide repeating units, spaced in approximately the same manner as the
24 repeats of E. coli LpxA. The P. aeruginosa UDP-GlcNAc acyltransferase is
54% identical and 67% similar to the E. coli enzyme. A plasmid (pGD3)
containing the 1.3-kb SalI-PstI fragment complemented E. coli RO138, a
temperature-sensitive mutant harboring lpxA2. LpxA assays of extracts of
this construct indicated that it is > 1,000-fold more selective for
3-hydroxydecanoyl-ACP than for 3-hydroxymyristoyl-ACP. Mass spectrometry of
lipid A isolated from this strain by hydrolysis at pH 4.5 revealed [M-H]-
1,684.5 (versus 1,796.5 for wild-type lipid A), consistent with
3-hydroxydecanoate rather than 3-hydroxymyristate at positions 3 and 3'.
Copyright © 1998, American Society for Microbiology
Expression cloning of a Pseudomonas gene encoding a hydroxydecanoyl- acyl carrier protein-dependent UDP-GlcNAc acyltransferase [In Process Citation]
Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA.
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