Formation of the single-layer beta-sheet of Borrelia burgdorferi OspA in the absence of the C-terminal capping globular domain.
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.
Huang
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X
Department of Biochemistry and Biophysics, University of Rochester Medical Center, 601 Elmwood Ave., Rochester, NY, 14642, USA
Nakagawa
T
T
Tamura
A
A
Link
K
K
Koide
A
A
Koide
S
S
D000595:Amino Acid Sequence; D000954:Antigens, Surface / Q000737:chemistry* / Q000378:metabolism*; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D001428:Bacterial Vaccines; D015748:Borrelia burgdorferi Group / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D006358:Hot Temperature; D008074:Lipoproteins; D022123:Lyme Disease Vaccines / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D018583:Pliability; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017384:Sequence Deletion
D000954:Antigens, Surface; D001425:Bacterial Outer Membrane Proteins; D001428:Bacterial Vaccines; D008074:Lipoproteins; D022123:Lyme Disease Vaccines; C072045:OspA protein; D010446:Peptide Fragments