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Journal of Bacteriology, November 2000, p. 6005-6013, Vol. 182, No. 21
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

The Haemophilus influenzae Hia Adhesin Is an Autotransporter Protein That Remains Uncleaved at the C Terminus and Fully Cell Associated

Joseph W. St. Geme III* and David Cutter

Edward Mallinckrodt Department of Pediatrics and Department of Molecular Microbiology, Washington University School of Medicine, and Division of Infectious Diseases, St. Louis Children's Hospital, St. Louis, Missouri

Received 23 June 2000/Accepted 16 August 2000

Nontypeable Haemophilus influenzae is a gram-negative commensal organism that is commonly associated with localized respiratory tract disease. The pathogenesis of disease begins with colonization of the nasopharynx, a process that likely depends on bacterial adherence to respiratory epithelial cells. Hia is the major adhesin expressed by a subset of nontypeable H. influenzae strains and promotes efficient adherence to a variety of human epithelial cell lines. Based on previous work, Hia is transported to the surface of Escherichia coli transformants and is capable of mediating E. coli adherence without the assistance of other H. influenzae proteins. In the present study, we examined the mechanism of Hia secretion. PhoA fusions, deletional mutagenesis, and N-terminal amino acid sequencing established that the signal for Hia export from the cytoplasm resides in the first 49 amino acids, including a 24-amino-acid stretch with striking similarity to the N terminus of a number of proteins belonging to the autotransporter family. Immunoelectron microscopy demonstrated that the Hia internal region defined by amino acids 221 to 779 is exposed on the bacterial surface. Secondary-structure analysis predicted that the C terminus of Hia forms a beta -barrel with a central hydrophilic channel, and site-specific mutagenesis and fusion protein analysis demonstrated that the C terminus targets Hia to the outer membrane and functions as an outer membrane translocator, analogous to observations with autotransporter proteins. In contrast to typical autotransporter proteins, Hia undergoes no cleavage between the internal and C-terminal domains and remains fully cell associated. Together, these results suggest that Hia is the prototype of an important subfamily of autotransporter proteins.

* Corresponding author. Mailing address: Department of Pediatrics, Washington University School of Medicine, 660 South Euclid Ave., Box 8208, St. Louis, MO 63110. Phone: (314) 286-2887. Fax: (314) 286-2895. E-mail: stgeme{at}borcim.wustl.edu.

Journal of Bacteriology, November 2000, p. 6005-6013, Vol. 182, No. 21
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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