Department of Physical Chemistry, Biochemistry and Inorganic Chemistry, Agrifood Campus of International Excellence (CeiA3), University of Almería, Spain.
Department of Applied Biology, Agrifood Campus of International Excellence (CeiA3), University of Almería, Spain.
FEBS J. 2012 Oct;279(19):3680-3691. doi: 10.1111/j.1742-4658.2012.08730.x. Epub 2012 Sep 4.
B-phycoerythrin from the red alga Porphyridium cruentum was crystallized using the technique of capillary counter-diffusion. Crystals belonging to the space group R3 with almost identical unit cell constants and diffracting to 1.85 and 1.70 Å were obtained at pH values of 5 and 8, respectively. The most important difference between structures is the presence of the residue His88α in two different conformations at pH 8. This residue is placed next to the chromophore phycoerythrobilin PEB82α and the new conformation results in the relocation of the hydrogen-bond network and hydration around PEB82α, which probably contributes to the observed pH dependence of the optical spectrum associated with this chromophore. Comparison with the structures of B-phycoerythrin from other red algae shows differences in the conformation of the A-ring of the chromophore PEB139α. This conformational difference in B-phycoerythrin from P. cruentum enables the formation of several hydrogen bonds that connect PEB139α with the chromophore PEB158β at the (αβ)(3) hexamer association interface. The possible influence of these structural differences on the optical spectrum and the ability of the protein to perform energy transfer are discussed, with the two pH-dependent conformations of His88α and PEB82α being proposed as representing critical structural features that are correlated with the pH dependence of the optical spectrum and transient optical states during energy transfer.
从红色海藻 Porphyridium cruentum 中提取的 B-藻红蛋白采用毛细对扩散技术进行结晶。在 pH 值分别为 5 和 8 时，获得了属于空间群 R3 的晶体，其晶胞常数几乎相同，可衍射至 1.85 和 1.70 Å。在 pH 8 时，结构之间最重要的区别是存在两个不同构象的残基 His88α。该残基位于发色团藻红胆素 PEB82α 的旁边，新构象导致 PEB82α 周围氢键网络和水合作用的重新定位，这可能导致与该发色团相关的光学光谱的观察到的 pH 依赖性。与其他红色海藻的 B-藻红蛋白结构的比较表明，发色团 PEB139α 的 A 环构象存在差异。这种来自 P. cruentum 的 B-藻红蛋白构象差异使 PEB139α 与发色团 PEB158β 在（αβ）（3）六聚体缔合界面上形成几个氢键。讨论了这些结构差异对光学光谱和蛋白质进行能量转移的能力的可能影响，并提出了 His88α 和 PEB82α 的两种 pH 依赖性构象，它们代表与光学光谱的 pH 依赖性和能量转移过程中瞬态光学状态相关的关键结构特征。
