Evidence for the Contribution of Point Mutations tovlsEVariation and for Apparent Constraints on the Net Accumulation of Sequence Changes invlsEduring Infection with Lyme Disease Spirochetes

Abstract

In the Lyme disease spirochetes, both the ospE and vlsE gene families have been demonstrated to undergo sequence variation during infection. To further investigate the mechanisms associated with the generation of vls variation, single-nucleotide polymorphism and subsequent DNA sequence analyses were performed on the vlsE gene and its paralog, BBJ51, a related gene with a frameshift mutation. These analyses focused on a series of postinfection clonal populations obtained from mice infected with Borrelia burgdorferi B31MIpc or its clonal derivative, B31MIc53. vlsE, but not BBJ51, was found to undergo sequence changes during infection. Consistent with that reported previously (J.-R. Zhang et al., Cell 89:275-285, 1997) many of the sequence changes appear to have arisen through gene conversion events and to be localized to the variable regions of vlsE. However, analysis of the vlsE nucleotide sequences revealed that some sequence changes were the result of point mutations, as these changes did not have potential contributing sources in the vls cassettes. To determine if sequence changes accumulate in vlsE over long-term infection, the vlsE genes of clonal populations recovered after 7 months of infection in mice were analyzed. While new sequence changes developed, a significant number of these changes resulted in the restoration of the vlsE sequence of the original infecting clone. In addition, we noted that some positions within the variable regions (VR) are stable even though the cassettes possess residues that could contribute to sequence variation through gene conversion. These analyses suggest that the total number of amino acid sequence changes that can be maintained by VlsE levels off during infection. In summary, in this report we demonstrate that the development of point mutations serves as a second mechanism by which vlsE sequence variation can be generated and that the capacity for vlsE variation, while still significant, is less than previously postulated.

Crystal Structure of Lyme Disease Variable Surface Antigen VlsE of Borrelia burgdorferi

“…vlsE gene expression is increased following exposure of B. burgdorferi to endothelial cell membranes or intact endothelial cells in vitro (29), indicating that VlsE may fall into a growing class of genes that are up-regulated in the mammalian environment. Furthermore, vlsE recombination occurs at a rapid rate during infection of either immunocompetent or immunodeficient mice but has not been detected during in vitro culture (7,30). It was reported by Ohnishi and de Silva (31) that B. burgdorferi in ticks inoculated by feeding on infected mice contained vlsE sequence variants that either arose within the ticks or were selected during the second feeding.…”

Putative Coiled-Coil Structural Elements of the BBA68 Protein of Lyme Disease Spirochetes Are Required for Formation of Its Factor H Binding Site

“…It is evident from the chronic nature of Lyme disease that the Lyme disease spirochetes are able to evade immune destruction. Several potential mechanisms of immune evasion have been identified (22,23,33,34,36,37). It has recently been demonstrated that some Borrelia species can bind the complement regulatory proteins factor H and or factor H like-protein 1 (FHL-1) to their surface (2,18,24,29).…”

Comparison of an automated Borrelia indirect chemiluminescent immunoassay (CLIA) with a VlsE/C6 ELISA and Immunoblot

“…Borrelia Outer surface protein C (OspC) [3] and Vmplike sequence expressed (VlsE) [4] are two plasmid encoded membrane proteins that both are immunodominant antigens. Furthermore, VlsE consists of one invariable region (IR6), which is extraordinary immunodominant [5,6].…”