, 1997; Casjens et al., 2000). Although the B. burgdorferi chromosome is rather small (approximately one megabase), the complexity and large sizes of many of the plasmids (some larger than 50 kb) greatly expand the DNA coding capacity of this spirochete. At the same time, however, it is currently poorly understood what role surface proteins encoded by genes on the various plasmids contribute to virulence and/or disease pathogenesis. The data accumulated thus far overwhelmingly support the hypothesis that plasmid-encoded proteins

are important in Lyme disease pathogenesis Talazoparib in vitro and could encode antigens that are important virulence factors and/or potential vaccinogens for Lyme disease. Given that the first vaccine developed for Lyme disease was generated against the fairly well conserved, plasmid-encoded OspA, it seems likely that HKI 272 the identification of another outer surface protein that is well conserved throughout borrelial genospecies would be a viable candidate for a developing a new vaccine molecule. This review outlines the outer surface proteins that have been identified thus far in various borrelial species, although the main focus is on the type

strain B. burgdorferi strain B31. The outer surface proteins described below fall into two main categories, lipid-modified outer surface proteins that are anchored to the outer leaflet of the outer membrane through their lipid moieties (e.g. OspA, OspB, OspC, OspD, OspE, OspF, DbpA, DbpB, CspA, VlsE, BptA, and several others with no known function) and outer surface proteins that have one or more transmembrane domains that anchor them into the outer membrane (e.g. P13, P66, BesC, BamA, Lmp1, and BB0405). The sections following provide a detailed examination of what is currently known about outer surface lipoproteins and membrane-spanning OMPs of B. burgdorferi. The B. burgdorferi genome Amylase encodes several lipoproteins that are localized to the surface of B. burgdorferi (Fraser et al., 1997; Casjens

et al., 2000). The surface lipoproteins of B. burgdorferi are now well recognized as important virulence determinants. As mentioned previously, because of the extracellular nature of this pathogen, surface lipoproteins play an important role in virulence, host–pathogen interactions, and in maintaining the enzootic cycle of B. burgdorferi. Several borrelial surface lipoproteins have been identified that bind host proteins and promote the adherence to host cells. For instance, B. burgdorferi lipoproteins bind host glycosaminoglycans (GAGs), decorin, and fibronectin. Furthermore, lipoproteins have been implicated in evasion of the host immune response through antigenic variation and evasion of complement deposition.