College of Pharmaceutical Sciences, Ritsumeikan University, Shiga, Japan.
Biophys J. 2012 Feb 22;102(4):916-26. doi: 10.1016/j.bpj.2011.12.010. Epub 2012 Feb 21.
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 (15)N/(1)H 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 ΔG(0) = 32 ± 9 kJ/mol and ΔV(0) = -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.
外表面蛋白 A(OspA)是伯氏疏螺旋体感染莱姆病的关键蛋白。我们通过高压(15)N/(1)H 二维 NMR 以及高压荧光光谱研究了 OspA 的构象波动。我们在折叠的天然 OspA 中发现了证据,表明在连接 N 端和 C 端结构域的非球形单层 β-折叠中,多肽主链的快速局部波动,τ<<ms,这可能使两个结构域在移动性和热力学稳定性方面具有一定的独立性。此外,我们发现折叠的天然 OspA 与小部分构象 I 处于平衡(τ>>ms),构象 I 几乎完全无序且水化,覆盖了整个多肽链的 C 端部分,从β8 到 C 端。构象 I 的特征为 ΔG(0)=32±9 kJ/mol 和 ΔV(0)=-140±40 mL/mol,在 40°C 和 0.1 MPa、pH 5.9 的条件下仅占 0.001%左右。由于在折叠构象中,OspA 的受体结合表位被埋藏在 C 端结构域中,因此在体内条件下,它向构象 I 的转变对于伯氏疏螺旋体的感染可能是关键的。这种特殊构象 I 的形成和稳定性显然得到了位于 C 端结构域中的大包装缺陷或腔的支持。