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Journal of Bacteriology, July 2005, p. 4656-4664, Vol. 187, No. 13
0021-9193/05/$08.00+0 doi:10.1128/JB.187.13.4656-4664.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Twyla Juehne, and
Joseph W. St. Geme III*
Edward Mallinckrodt Department of Pediatrics and Department of Molecular Microbiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, Missouri 63110
Received 13 January 2005/ Accepted 14 March 2005
Haemophilus influenzae type b is an important cause of meningitis and other serious invasive diseases and initiates infection by colonizing the upper respiratory tract. Among the major adhesins in H. influenzae type b is a nonpilus protein called Hsf, a large protein that forms fiber-like structures on the bacterial surface and shares significant sequence similarity with the nontypeable H. influenzae Hia autotransporter. In the present study, we characterized the structure and adhesive activity of Hsf. Analysis of the predicted amino acid sequence of Hsf revealed three regions with high-level homology to the HiaBD1 and HiaBD2 binding domains in Hia. Based on examination of glutathione S-transferase fusion proteins corresponding to these regions, two of the three had adhesive activity and one was nonadhesive in assays with cultured epithelial cells. Structural modeling demonstrated that only the two regions with adhesive activity harbored an acidic binding pocket like the binding pocket identified in the crystal structure of HiaBD1. Consistent with these results, disruption of the acidic binding pockets in the adhesive regions eliminated adhesive activity. These studies advance our understanding of the architecture of Hsf and the family of trimeric autotransporters and provide insight into the structural determinants of H. influenzae type b adherence.
Present address: Department of Biochemistry, University of Houston, Houston, Texas.
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