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Int J Med Microbiol. 2015 Jan;305(1):27-37. doi: 10.1016/j.ijmm.2014.10.004. Epub 2014 Oct 27.

Haemophilus influenzae surface fibril (Hsf) is a unique twisted hairpin-like trimeric autotransporter.

Author information

1
Medical Microbiology, Department of Laboratory Medicine Malmö, Lund University, Jan Waldenströms gata 59, SE-205 02 Malmö, Sweden.
2
Infection Medicine, Department of Clinical Sciences, Lund University, SE-221 84 Lund, Sweden.
3
Centre for Analysis and Synthesis, Department of Chemistry, Lund University, PO Box 124, SE-221 00 Lund, Sweden.
4
Biochemistry and Structural Biology, Lund University, PO Box 124, SE-221 00 Lund, Sweden.
5
Medical Microbiology, Department of Laboratory Medicine Malmö, Lund University, Jan Waldenströms gata 59, SE-205 02 Malmö, Sweden. Electronic address: kristian.riesbeck@med.lu.se.

Abstract

The Haemophilus surface fibril (Hsf) is an extraordinary large (2413 amino acids) trimeric autotransporter, present in all encapsulated Haemophilus influenzae. It contributes to virulence by directly functioning as an adhesin. Furthermore, Hsf recruits the host factor vitronectin thereby inhibiting the host innate immune response resulting in enhanced survival in serum. Here we observed by electron microscopy that Hsf appears as an 100 nm long fibril at the bacterial surface albeit the length is approximately 200 nm according to a bioinformatics based model. To unveil this discrepancy, we denaturated Hsf at the surface of Hib by using guanidine hydrochloride (GuHCl). Partial denaturation induced in the presence of GuHCl unfolded the Hsf molecules, and resulted in an increased length of fibres in comparison to the native trimeric form. Importantly, our findings were also verified by E. coli expressing Hsf at its surface. In addition, a set of Hsf-specific peptide antibodies also indicated that the N-terminal of Hsf is located near the C-terminal at the base of the fibril. Taken together, our results demonstrated that Hsf is not a straight molecule but is folded and doubled over. This is the first report that provides the unique structural features of the trimeric autotransporter Hsf.

KEYWORDS:

Haemophilus influenzae type b; Haemophilus surface fibril; Hib; Hsf

PMID:
25465160
DOI:
10.1016/j.ijmm.2014.10.004
[Indexed for MEDLINE]

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