Formation of the single-layer beta-sheet of Borrelia burgdorferi OspA in the absence of the C-terminal capping globular domain

J Mol Biol. 2001 Apr 27;308(2):367-75. doi: 10.1006/jmbi.2001.4579.


Borrelia outer surface protein A (OspA) contains a unique single-layer beta-sheet that connects N and C-terminal globular domains. This single-layer beta-sheet segment (beta-strands 8-10) is highly stable in solution, although it is exposed to the solvent on both faces of the sheet and thus it does not contain a hydrophobic core. Here, we tested whether interactions with the C-terminal domain are essential for the formation of the single-layer beta-sheet. We characterized the solution structure, dynamics and stability of an OspA fragment corresponding to beta-strands 1-12 (termed OspA[27-163]), which lacks a majority of the C-terminal globular domain. Analyses of NMR chemical shifts and backbone nuclear Overhauser effect (NOE) connectivities showed that OspA[27-163] is folded except the 12th and final beta-strand. (1)H-(15)N heteronuclear NOE measurements and amide H-(2)H exchange revealed that the single-layer beta-sheet in this fragment is more flexible than the corresponding region in full-length OspA. Thermal-denaturation experiments using differential scanning calorimetry and NMR spectroscopy revealed that the N-terminal globular domain in the fragment has a conformational stability similar to that of the same region in the full-length protein, and that the single-layer beta-sheet region also has a modest thermal stability. These results demonstrate that the unique single-layer beta-sheet retains its conformation in the absence of its interactions with the C-terminal domain. This fragment is significantly smaller than the full-length OspA, and thus it is expected to facilitate studies of the folding mechanism of this unusual beta-sheet structure.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Antigens, Surface / chemistry*
  • Antigens, Surface / metabolism*
  • Bacterial Outer Membrane Proteins / chemistry*
  • Bacterial Outer Membrane Proteins / metabolism*
  • Bacterial Vaccines
  • Borrelia burgdorferi Group / chemistry*
  • Calorimetry, Differential Scanning
  • Hot Temperature
  • Lipoproteins*
  • Lyme Disease Vaccines / chemistry*
  • Lyme Disease Vaccines / metabolism*
  • Models, Molecular
  • Molecular Sequence Data
  • Nuclear Magnetic Resonance, Biomolecular
  • Peptide Fragments / chemistry
  • Peptide Fragments / metabolism
  • Pliability
  • Protein Denaturation
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Sequence Deletion


  • Antigens, Surface
  • Bacterial Outer Membrane Proteins
  • Bacterial Vaccines
  • Lipoproteins
  • Lyme Disease Vaccines
  • OspA protein
  • Peptide Fragments