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Infection and Immunity, June 2009, p. 2376-2384, Vol. 77, No. 6
0019-9567/09/$08.00+0     doi:10.1128/IAI.01446-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Lex2B, a Phase-Variable Glycosyltransferase, Adds either a Glucose or a Galactose to Haemophilus influenzae Lipopolysaccharide{triangledown}

M. E. Deadman,1 P. Hermant,1 M. Engskog,2 K. Makepeace,1 E. R. Moxon,1 E. K. H. Schweda,2 and D. W. Hood1*

Molecular Infectious Diseases Group, University of Oxford, Department of Paediatrics, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford OX3 9DS, United Kingdom,1 Clinical Research Centre, Karolinska Institutet and University College of South Stockholm, NOVUM, S-141 86 Huddinge, Sweden2

Received 25 November 2008/ Returned for modification 8 January 2009/ Accepted 4 March 2009

Nontypeable Haemophilus influenzae is a commensal that frequently causes otitis media and respiratory tract infections. The lex2 locus encodes a glycosyltransferase that is phase variably expressed and contributes to the significant intrastrain heterogeneity of lipopolysaccharide (LPS) composition in H. influenzae. In serotype b strains, Lex2B adds the second β-glucose in the oligosaccharide extension from the proximal heptose of the triheptose inner core backbone; this extension includes a digalactoside that plays a role in resistance of the bacteria to the killing effect of serum. As part of our studies of the structure and genetics of LPS in nontypeable H. influenzae, we show here that there are allelic polymorphisms in the lex2B sequence that correlate with addition of either a glucose or a galactose to the same position in the LPS molecule across strains. Through exchange of lex2 alleles between strains we show that alteration of a single amino acid at position 157 in Lex2B appears to be sufficient to direct the alternative glucosyl- or galactosyltransferase activities. Allelic exchange strains express LPS with altered structure and biological properties compared to the wild-type LPS. Thus, Lex2B contributes to both inter- and intrastrain LPS heterogeneity through its polymorphic sequences and phase-variable expression.

* Corresponding author. Mailing address: Molecular Infectious Diseases Group, University of Oxford, Department of Paediatrics, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford OX3 9DS, United Kingdom. Phone: (44) 1865 222347. Fax: (44) 1865 222626. E-mail: derek.hood{at}paediatrics.ox.ac.uk

{triangledown} Published ahead of print on 16 March 2009.

Editor: J. N. Weiser

Infection and Immunity, June 2009, p. 2376-2384, Vol. 77, No. 6
0019-9567/09/$08.00+0     doi:10.1128/IAI.01446-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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