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Title: Characterisation and structural studies of a superoxide dismutase and OmpA-like proteins from Borrelia burgdorferi sensu lato
Author: Brown, Gemma
ISNI:       0000 0004 6347 9506
Awarding Body: University of Huddersfield
Current Institution: University of Huddersfield
Date of Award: 2016
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Lyme borreliosis is the most common tick-borne, human infection across the Northern hemisphere. The agent responsible, Borrelia burgdorferi sensu lato (s.l.) covers a family of Spirochaetes with unique characteristics which are shared by both Gram-negative and Grampositive bacteria. The outer membrane (OM) is rich in lipoproteins but contains a relatively low density of integral membrane proteins (OMPs), of these OMPs very few have been identified and even fewer are well characterised. The OmpA-like transmembrane domain defined by the Pfam family PF01389 is a 8-stranded membrane spanning β-barrel and is well conserved among Gram-negative bacteria but to date remains unknown in Spirochaetes. Building from previous computational work which had sought to identify possible OMPs from B. burgdorferi s.l. four OmpA-like proteins, BAPKO_0422 (Borrelia afzelii), BB_0562, BB_0406 (B. burgdorferi) and BG0408 (Borrelia garinii) have been identified and structurally characterised. The four proteins are encoded by chromosomal genes and highly conserved between Borrelia species and may be of diagnostic or therapeutic value. Structural characterisation by both circular dichroism and small angle X-ray scattering suggests these four proteins adopt a compact globular structure rich in β-strand (~40%) with Ab initio molecular envelopes resembling a cylindrical peanut shape with dimensions of ~25x45 Å consistent with an 8-stranded β-barrel. The present work demonstrates that BAPKO_0422 can bind human factor H (hfH) and some evidence for a further interaction between the BAPKO_0422 protein and heparin. The interaction with hfH may contribute to the spirochaete’s immune evasion mechanisms by the inhibition of the complement response. The zoonotic life-cycle of Borrelia and challenges by the host’s immune system causes an ever changing environment which often leads to fluctuations of O2 exposure. Although B. burgdorferi s.l. have a distinct lack of metabolic systems including peroxidases and catalase enzymes the Spirochaetes genome does encode a single superoxide dismutase gene (sodA - bb_0157). Previously assigned as a Fe-SOD there has been some debate whether this protein requires iron or manganese as a co-factor. The present work demonstrates that the B. burgdorferi enzyme SodA requires manganese for activity and does not display cambialistic behaviour. Structural and proteomic characterisation suggests the B. burgdorferi SodA enzyme shares significant sequence similarity to a superoxide dismutase from Thermus thermophilus.
Supervisor: Bingham, Richard Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QH301 Biology