OspA

Rapid Prototyping of of Borrelia burgdorferi

OspA (Outer surface protein A) is an abundant lipoprotein of the causative agent of Lyme disease, Borrelia burgdorferi spirochete. Its purpose is to stimulate the production of specific antibodies against B. burgdorferi and is used as a vaccination against Lyme disease, the disease carried by ticks(1).

It is a borrelial protein that colonizes within the transmitting tick host midgut. Lyme disease is a progressive infection resulting from inoculation of the spirochete Borrelia burgdorferi into the skin by a feeding tick, usually Ixodes species (2); if left untreated; it may progress in many stages beginning from minor symptoms like rash, commonly seen as a bull-eyes rash and then progress into serious, lifelong disabilities. It is known to cause demyelinating diseases in the central nervous system.  One of the autoimmune process triggers, resulting in the demyelinating disease, occurs from the endurance of the Borrelia in the host. Once the spirochete is in the Central Nervous System, OspA is up regulated for the sake of adhesion to the area. (6)  OspA is up-regulated when the protein is inside the transmitting tick host and begins down regulation upon infection of the mammalian host. Blockage of spirochete transmission from the tick vector to the mammalian host by anti-OspA antibodies appears to be the main mechanism of protection by the immunological response. (3) However, further studies need to be done in order to improve the OspA based vaccines. 

Here, a 3-D prototype was created to portray its structures. OspA is composed of a prolonged fold with 21 anti-parallel Beta sheets and a single alpha helix. They are arranged to form the N-terminal, central sheet and C –terminal barrel domains OspA has numerous features, including a unique folding pattern that includes alternating charge arrays into antiparallel β-sheet, a potential ligand binding site, a conserved surface overlapping the epitope of the Fab, and a distinctive variable motif. It suggests that the protein has a conserved function, possibly acting as a receptor or signal transducer. (2) Although OspA normally has a lipidated N-terminal cysteine to provide a membrane anchor (4), a recombinant unlipidated form is soluble in aqueous solution and is still recognized by antibodies from Lyme disease patients (5). It was identified that three loops of connecting beta strands are the primary sites of binding. , colored red on the 3-D prototype, consists of residues 203 to 220. However, a natural variation found on colored yellow, of the first loop is a significant limiting factor in the antibody binding. , colored purple, consists of residues 224 to 233. And , colored blue, consists of residues 246 to 257. The remainder of the beta sheets was colored cyan because they did not play any significant role in OspA. This prototype suggests the importance of the three specific loops and their purpose to binding.

References Brandt M E, Riley B S, Radolf J D, Norgard M V (1990) Infect Immun58:983–991 "Crystal Structure of Lyme Disease Antigen Outer Surface Protein A Complexed With an L-Fab." Crystal Structure of Lyme Disease Antigen Outer Surface Protein A Complexed With an L-Fab. Web. 20 Apr. 2012. <http://www.pnas.org/content /94/8/3584.full>. de Silva A M, Telford S R III, Brunet L R, Barthold S W, Fikrig (1996) J Exp Med 183:271– 275 "DrugBank: OspA Lipoprotein (DB00045)." DrugBank. Web. 20 Apr. 2012. <http://www. drugbank.ca/drugs/DB00045>. Dunn J J, Lade B N, Barbour A G(1990) Protein Expression Purif 1:159–168 Durovska,J,S Bazovska, et al. “infection with B.burgdorferi s.l., and the CNS demyelinating disease. A case report.” PubMed. 32.4 (2011):411-414. 20 Apr.2012. <pubmed.gov>. Rupprecht, Tobias A. “The Pathogenesis of Lyme Neuroborreliosis: From Infection to Inflammation.” MOL MED. (2008): 205-212.