A delicate interplay of structure, dynamics, and thermodynamics for function: a high pressure NMR study of outer surface protein A |
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Authors: | Kitahara Ryo Simorellis Alana K Hata Kazumi Maeno Akihiro Yokoyama Shigeyuki Koide Shohei Akasaka Kazuyuki |
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Affiliation: | College of Pharmaceutical Sciences, Ritsumeikan University, Shiga, Japan. |
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Abstract: | Outer surface protein A (OspA) is a crucial protein in the infection of Borrelia burgdorferi causing Lyme disease. We studied conformational fluctuations of OspA with high-pressure 15N/1H two-dimensional NMR along with high-pressure fluorescence spectroscopy. We found evidence within folded, native OspA for rapid local fluctuations of the polypeptide backbone in the nonglobular single layer β-sheet connecting the N- and C-terminal domains with τ << ms, which may give the two domains certain independence in mobility and thermodynamic stability. Furthermore, we found that folded, native OspA is in equilibrium (τ >> ms) with a minor conformer I, which is almost fully disordered and hydrated for the entire C-terminal part of the polypeptide chain from β8 to the C-terminus. Conformer I is characterized with ΔG0 = 32 ± 9 kJ/mol and ΔV0 = −140 ± 40 mL/mol, populating only ∼0.001% at 40°C at 0.1 MPa, pH 5.9. Because in the folded conformer the receptor binding epitope of OspA is buried in the C-terminal domain, its transition into conformer I under in vivo conditions may be critical for the infection of B. burgdorferi. The formation and stability of the peculiar conformer I are apparently supported by a large packing defect or cavity located in the C-terminal domain. |
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