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Infect. Immun., 04 1995, 1356-1361, Vol 63, No. 4
BC McGrath, JJ Dunn, G Gorgone, D Guttman, D Dykhuizen and BJ Luft
The gene for the major outer surface protein A (OspA) from several
clinically obtained strains of Borrelia burgdorferi, the cause of Lyme
disease, has been cloned, sequenced, and expressed in Escherichia coli by
using a T7-based expression system (J. J. Dunn, B. N. Lade, and A. G.
Barbour, Protein Expr. Purif. 1:159-168, 1990). All of the OspAs have a
single conserved tryptophan at residue 216 or, in some cases, 217; however,
the region of the protein flanking the tryptophan is hypervariable, as
determined by a moving-window population analysis of ospA from 15 European
and North American isolates of B. burgdorferi. Epitope-mapping studies
using chemically cleaved OspA and a TrpE-OspA fusion have indicated that
this hypervariable region is important for immune recognition. Biophysical
analysis, including fluorescence and circular dichroism spectroscopy, have
indicated that the conserved tryptophan is buried in a hydrophobic
environment. Polar amino acid side chains flanking the tryptophan are
likely to be exposed to the hydrophilic solvent. The hypervariability of
these solvent-exposed amino acid residues may contribute to the antigenic
variation in OspA. To test this, we have performed site-directed
mutagenesis to replace some of the potentially exposed amino acid side
chains in the B31 protein with the analogous residues of a Borrelia garinii
strain, K48. The altered proteins were then analyzed by Western blot
(immunoblot) with monoclonal antibodies which bind OspA on the surface of
the intact B31 spirochete. Our results indicate that specific amino acid
changes near the tryptophan can abolish the reactivity of OspA to these
monoclonal antibodies, which is an important consideration in the design of
vaccines based on recombinant OspA.
Copyright © 1995, American Society for Microbiology
Identification of an immunologically important hypervariable domain of major outer surface protein A of Borrelia burgdorferi [published erratum appears in Infect Immun 1995 Jun;63(6):2390]
Biology Department, Brookhaven National Laboratory, Upton, New York 11973.
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