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J. Bacteriol., 03 1996, 1265-1273, Vol 178, No. 5
CM Kahler, RW Carlson, MM Rahman, LE Martin and DS Stephens
A lipooligosaccharide (LOS) mutant of Neisseria meningitidis serogroup B
strain NMB (immunotype L3,7,9) was identified in a Tn916 (tetM) mutant bank
by loss of reactivity with monoclonal antibody 3F11, which recognizes the
terminal Galbeta1-->4GlcNAc epitope in the lacto-N- neotetraose moiety
of the wild-type LOS structure. The mutant, designated 559, was found to
express a truncated LOS of 3.0 kDa. Southern and PCR analyses demonstrated
that there was a single intact Tn916 insertion (class I) in the mutant 559
chromosome. Linkage of the LOS phenotype and the Tn916 insertion was
confirmed by transformation of the wild-type parent. Nucleotide sequence
analysis of the region surrounding the transposition site revealed a
1,065-bp open reading frame (ORF). A homology search of the GenBank/EMBL
database revealed that the amino acid sequence of this ORF had 46.8%
similarity and 21.2% identity with the alpha1,2 N-acetylglucosamine
transferase (RfaK) from Salmonella typhimurium. Glycosyl composition and
linkage analysis of the LOS produced by mutant 559 revealed that the
lacto-N-neotetraose group which is attached to heptose I (HepI) and the
N-acetylglucosamine and glucose residues that are attached to HepII in the
inner core of the parental LOS were absent. These analyses also showed that
the HepII residue in both the parent and the mutant LOS molecules was
phosphorylated, presumably by a phosphoethanolamine substituent. The
insertion of nonpolar and polar antibiotic resistance cartridges into the
parental rfaK gene resulted in the expression of LOS with the same mobility
as that produced by mutant 559. This result indicated that the inability to
add the lacto-N-neotetraose group to the 559 LOS is not due to a polar
effect on a gene(s) downstream of rfaK. Our data indicate that we have
identified the meningococcal alpha1,2 N- acetylglucosamine transferase
responsible for the addition of N- acetylglucosamine to HepII. We propose
that the lack of alpha-chain extension from HepI in the LOS of mutant 559
may be due to structural constraints imposed by the incomplete biosynthesis
of the LOS inner core.
Copyright © 1996, American Society for Microbiology
Inner core biosynthesis of lipooligosaccharide (LOS) in Neisseria meningitidis serogroup B: identification and role in LOS assembly of the alpha1,2 N-acetylglucosamine transferase (RfaK)
Division of Infectious Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia, USA.
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