Borrelia burgdorferi RevA Antigen Is a Surface-Exposed Outer Membrane Protein Whose Expression Is Regulated in Response to Environmental Temperature and pH

Abstract

Borrelia burgdorferi, the causative agent of Lyme disease, produces RevA protein during the early stages of mammalian infection. B. burgdorferi apparently uses temperature as a cue to its location, producing proteins required for infection of warm-blooded animals at temperatures corresponding to host body temperature, but does not produce such virulence factors at cooler, ambient temperatures. We have observed that B. burgdorferi regulates expression of RevA in response to temperature, with the protein being synthesized by bacteria cultivated at 34°C but not by those grown at 23°C. Tissues encountered by B. burgdorferi during its infectious cycle vary in their pH values, and the level of RevA expression was also found to be dependent upon pH of the culture medium. The cellular localization of RevA was also analyzed. Borrelial inner and outer membranes were purified by isopycnic centrifugation, and membrane fractions were conclusively identified by immunoblot analysis using antibodies raised against the integral inner membrane protein MotB and outer membraneassociated Erp lipoproteins. Immunoblot analyses indicated that RevA is located in the B. burgdorferi outer membrane. These analyses also demonstrated that an earlier report (H. A. Bledsoe et al., Infect. Immun. 176:7447-7455, 1994) had misidentified such B. burgdorferi membrane fractions. RevA was further demonstrated to be exposed to the external environment, where it could facilitate interactions with host tissues.The spirochete Borrelia burgdorferi has evolved efficient mechanisms by which it can persistently infect both warmblooded and arthropod hosts and be efficiently transmitted between these two host types (49). Such a complex lifestyle requires that the bacteria produce proteins appropriate for each stage of the infectious cycle. These might include surface proteins that facilitate interactions with host cells or extracellular components, function in nutrient acquisition, or help protect the bacteria against host immune system responses. Throughout its infectious cycle, B. burgdorferi apparently senses its location in order to produce proteins and other factors required for each stage of the cycle. We and others have demonstrated that B. burgdorferi recognizes various environmental cues, including temperature, pH, and soluble chemicals and, as a consequence, regulates surface protein expression (1-3, 12, 13, 30, 40, 45, 46, 50, 51, 54, 55, 62).Among the B. burgdorferi proteins known to be synthesized during mammalian infection is an approximately 17-kDa protein previously designated Rev (25,43,53) and herein renamed RevA (see below for the rationale behind this name modification). All analyzed Lyme disease spirochetes contain numerous different, but largely homologous, plasmids of the cp32 family (15,16,56). RevA proteins are encoded by some, but not all, cp32s: B. burgdorferi type strain B31 contains two revA alleles, one each on cp32-1 and cp32-6 (15). To date, only three additional strains of B. burgdorferi have been examined for this gene, but al...

Borrelia burgdorferi cp32 BpaB Modulates Expression of the Prophage NucP Nuclease and SsbP Single-Stranded DNA-Binding Protein

“…The cp32 elements of Lyme disease spirochetes, such as B. burgdorferi, are of particular interest, since they encode Erp, RevA, and Mlp lipoproteins. These bacterial surface proteins are produced by the bacterium during mammalian infection, and those with known functions serve as adhesins for host components, such as plasmin(ogen), laminin, and complement factor H (1,7,8,9,10,13,22,25,26,32,33,38,42,43,49,63). Sequences of the erp, revA, and mlp loci generally vary between different cp32s (Fig.…”

A Novel Gene Inactivation System Reveals Altered Periplasmic Flagellar Orientation in aBorrelia burgdorferi fliLMutant

“…burgdorferi MotB from J. Carroll (RML, NIH, Hamilton, MT). The reactivities of those antibodies to B. burgdorferi FlaB, FliM, and MotB were reported previously (8,35,43,46,51).…”

Simultaneous Coexpression ofBorrelia burgdorferiErp Proteins Occurs through a Specific,erpLocus-Directed Regulatory Mechanism

“…Cultured bacteria were incubated with protease, with the idea that surface-exposed proteins of intact bacteria will be degraded, whereas those below the surface will remain untouched. Since a number of borrelial outer surface proteins are resistant to some proteolytic enzymes (10,12,22,25,50), two different enzymes were used in these studies. The results of these experiments showed that neither protease degraded BppC (data not shown).…”