Haemophilus influenzae type b (Hib) is a Gram-negative bacterium that causes meningitis in infants. Located in the outer membrane, Hib porin (342 amino acids, M$ rm sb{r}$ 37,782 daltons) forms channels that allow for the diffusion into the periplasm of small solutes up to a molecular mass of 1400 daltons. / Based on predictions of porin secondary structure, a model of Hib porin was generated. The model proposed sixteen membrane spanning $ beta$-strands connected by eight long loops on one side and eight short $ beta$-turns on the other side. To refine further this model, the epitopes of nine monoclonal antibodies specific for Hib porin were mapped precisely. Surface-exposure of these epitopes was determined by flow cytometry of intact Hib cells. Our studies identified two surface-exposed regions of Hib porin: amino acids 162 to 172, and 318 to 325. These two regions correspond to loops 4 and 8 in the Hib porin model. / Three naturally occurring Hib porin variants were purified, reconstituted into planar bilayers, and analyzed for their voltage dependency. Substitutions at Arg166 residue, which is localized to loop 4, were associated with a lowered threshold potential for the voltage gating of Hib porin. This surface-exposed loop was therefore implicated in the conformational changes that are postulated to occur during voltage gating. / Lipooligosaccharide (LOS) binds tightly to Hib porin. To generate large amounts of Hib porin devoid of LOS, the ompP2 gene was cloned into an expression vector of Bacillus subtilis. Recombinant Hib porin was produced in large quantities and it aggregated into inclusion bodies. Under denaturing conditions, recombinant porin was purified to homogeneity and subsequently refolded. To assess the fidelity of refolding of recombinant porin, four criteria were used: spectroscopic properties, channel formation in planar bilayers, resistance to trypsin digestion and formation of the conformational epitope recognized by monoclonal antibody Hb-2. We conclude that in the absence of LOS, recombinant porin was refolded into a functional form, its structure closely resembling the native state.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.42009 |
| Date | January 1996 |
| Creators | Dahan, David. |
| Contributors | Coulton, J. W. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Microbiology and Immunology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001629395, proquestno: NQ29916, Theses scanned by UMI/ProQuest. |
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