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Infection and Immunity, June 2004, p. 3418-3428, Vol. 72, No. 6
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.6.3418-3428.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

A Novel Lectin, DltA, Is Required for Expression of a Full Serum Resistance Phenotype in Haemophilus ducreyi

Isabelle Leduc,1 Patricia Richards,2 Crystal Davis,3 Birgit Schilling,4 and Christopher Elkins1,5*

Departments of Medicine,1 Microbiology and Immunology, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599,5 Howard University College of Medicine, Washington, D.C. 20059,2 Department of Microbiology and Immunology, School of Medicine, University of Louisville, Louisville, Kentucky 40202,3 Buck Institute for Age Research, Novato, California 949454

Received 17 October 2003/ Returned for modification 1 December 2003/ Accepted 8 March 2004

Haemophilus ducreyi, the causative agent of chancroid, is highly resistant to the complement-mediated bactericidal activity of normal human serum (NHS). Previously, we identified DsrA (for ducreyi serum resistance A), a major factor required for expression of the serum resistance phenotype in H. ducreyi. We describe here a second outer membrane protein, DltA (for ducreyi lectin A), which also contributes to serum resistance in H. ducreyi. Isogenic dltA mutants, constructed in 35000HP wild-type and FX517 dsrA backgrounds, were more susceptible to the bactericidal effects of NHS than each respective parent, demonstrating the additive effect of the mutations. Furthermore, expression of dltA in H. influenzae strain Rd rendered this highly susceptible strain partially resistant to 5% NHS compared to a vector-control strain. Although primary basic local alignment search tool analysis of the dltA open reading frame revealed no close bacterial homologue, similarity to the ß-chain of the eukaryotic lectin ricin was noted. DltA shares highly conserved structural motifs with the ricin ß chain, such as cysteines and lectin-binding domains. To determine whether dltA was a lectin, ligand blots and affinity chromatography experiments were performed. DltA was affinity purified on immobilized lactose and N-acetylgalactosamine, and N-glycosylated but not glycosidase-treated model glycoproteins bound DltA. These data indicate that DltA is a lectin with specificity for lactose-related carbohydrates (CHO) and is important for H. ducreyi serum resistance.

* Corresponding author. Mailing address: 8341C Medical Biomolecular Research Bldg., University of North Carolina at Chapel Hill, CB #7031, Chapel Hill, NC 27599. Phone: (919) 843-5521. Fax: (919) 843-1015. E-mail: chriselk{at}med.unc.edu.

Editor: D. L. Burns

Infection and Immunity, June 2004, p. 3418-3428, Vol. 72, No. 6
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.6.3418-3428.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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