Photosynth Res. 2013 Dec;118(3):231-47. doi: 10.1007/s11120-013-9920-4.
We present a molecular-scale model of Bacteriochlorophyll a (BChl a) binding to the chlorosome protein A (CsmA) of Chlorobaculum tepidum, and the aggregated pigment–protein dimer, as determined from protein–ligand docking and quantum chemistry calculations. Our calculations provide strong evidence that the BChl a molecule is coordinated to the His25 residue of CsmA, with the magnesium center of the bacteriochlorin ring situated\3 A° from the imidazole nitrogen atom of the histidine sidechain, and the phytyl tail aligned along the nonpolar residues of the a-helix of CsmA. We also confirm that the Qy band in the absorption spectra of BChl a experiences a large (?16 to ?43 nm) redshift when aggregated with another BChl a molecule in the CsmA dimer, compared to the BChl a in solvent; this redshift has been previously established by experimental researchers. We propose that our model of the BChl a–CsmA binding motif, where the dimer contains parallel aligned N-terminal regions, serves as the smallest repeating unit in a larger model of the para-crystalline chlorosome baseplate protein.
我们提出了一个分子尺度的模型，用于研究 Bacteriochlorophyll a（BChl a）与嗜热盐杆菌的 Chlorosome 蛋白 A（CsmA）的结合，以及聚集的色素-蛋白二聚体，这是通过蛋白质-配体对接和量子化学计算确定的。我们的计算提供了强有力的证据，表明 BChl a 分子与 CsmA 的 His25 残基配位，细菌叶绿素环的镁中心与组氨酸侧链的咪唑氮原子相距\3 A°，植基尾链沿着 CsmA 的α-螺旋的非极性残基排列。我们还证实，与溶剂中的 BChl a 相比，当 BChl a 在 CsmA 二聚体中与另一个 BChl a 分子聚集时，其 Qy 带在吸收光谱中经历了较大的红移（?16 至?43nm）；这一红移先前已被实验研究人员所证实。我们提出，我们的 BChl a-CsmA 结合基序模型，其中二聚体包含平行排列的 N 端区域，作为更大的准晶状 Chlorosome 基底蛋白模型中的最小重复单元。
