title: Haemophilus influenzae surface fibril (Hsf) is a unique twisted hairpin-like trimeric autotransporter.
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.
authors.affiliation: Medical Microbiology, Department of Laboratory Medicine Malmö, Lund University, Jan Waldenströms gata 59, SE-205 02 Malmö, Sweden.
authors.forename: Birendra
authors.initials: B
authors.lastname: Singh
authors.affiliation: Medical Microbiology, Department of Laboratory Medicine Malmö, Lund University, Jan Waldenströms gata 59, SE-205 02 Malmö, Sweden.
authors.forename: Tamim Al
authors.initials: TA
authors.lastname: Jubair
authors.affiliation: Infection Medicine, Department of Clinical Sciences, Lund University, SE-221 84 Lund, Sweden.
authors.forename: Matthias
authors.initials: M
authors.lastname: Mörgelin
authors.affiliation: Centre for Analysis and Synthesis, Department of Chemistry, Lund University, PO Box 124, SE-221 00 Lund, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Sundin
authors.affiliation: Biochemistry and Structural Biology, Lund University, PO Box 124, SE-221 00 Lund, Sweden.
authors.forename: Sara
authors.initials: S
authors.lastname: Linse
authors.affiliation: Centre for Analysis and Synthesis, Department of Chemistry, Lund University, PO Box 124, SE-221 00 Lund, Sweden.
authors.forename: Ulf J
authors.initials: UJ
authors.lastname: Nilsson
authors.affiliation: 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.
authors.forename: Kristian
authors.initials: K
authors.lastname: Riesbeck
mesh_terms: D018829:Adhesins, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006193:Haemophilus influenzae / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008854:Microscopy, Electron; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry / Q000648:ultrastructure; D011487:Protein Conformation; D037521:Virulence Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D018829:Adhesins, Bacterial; C102673:Hsf protein, bacteria; D026901:Membrane Transport Proteins; D046912:Multiprotein Complexes; D037521:Virulence Factors
keywords: Haemophilus influenzae type b; Haemophilus surface fibril; Hib; Hsf