Bron P, Lacapère J J, Breyton C, Mosser G
Section de Recherche UMR-CNRS 168 and LCR-CEA 8, Institut Curie, 11 rue Pierre et Marie Curie, Paris Cedex, 75231, France.
J Mol Biol. 1999 Mar 19;287(1):117-26. doi: 10.1006/jmbi.1999.2604.
Thin three-dimensional crystals of the cytochrome b6 f complex from the unicellular algae Chlamydomonas reinhardtii have been grown by BioBeads-mediated detergent removal from a mixture of protein and lipid solubilized in Hecameg. Frozen-hydrated crystals, exhibiting p22121 plane group symmetry, were studied by electron crystallography and a projection map at 9 A resolution was calculated. The crystals (unit cell dimensions of a=173.5 A, b=70.0 A and gamma=90.0 degrees) showed the presence of dimers, and within each monomer 14 domains of electron density were observed. The combination of the projection map obtained from ice-embedded crystals of cytochrome b6 f with a previous map obtained from negatively stained samples brings new insight in the organization of the complex. For example, it distinguishes some peaks and/or domains that are only extramembrane or transmembrane, and reveals the possible localization of single-stranded transmembrane alpha-helices (Pet subunits). Furthermore, the cross-correlation of our projection map from frozen hydrated samples with the atomic model of the transmembrane part of the cytochrome bc1 complex has allowed us to localize the cytochrome b6 at the dimer interface and to reveal structural differences between the two complexes.
通过BioBeads介导的去污剂去除法，从溶解于Hecameg中的蛋白质和脂质混合物中培养出了来自单细胞藻类莱茵衣藻的细胞色素b6 f复合物的薄三维晶体。通过电子晶体学研究了呈现p22121平面群对称性的冷冻水合晶体，并计算出了9埃分辨率的投影图。这些晶体（晶胞尺寸为a = 173.5埃，b = 70.0埃，γ = 90.0度）显示存在二聚体，并且在每个单体中观察到14个电子密度区域。从细胞色素b6 f的冰包埋晶体获得的投影图与先前从负染样品获得的图相结合，为该复合物的组织带来了新的见解。例如，它区分了仅位于膜外或跨膜的一些峰和/或区域，并揭示了单链跨膜α螺旋（Pet亚基）的可能定位。此外，我们从冷冻水合样品获得的投影图与细胞色素bc1复合物跨膜部分的原子模型的互相关，使我们能够将细胞色素b6定位在二聚体界面，并揭示这两种复合物之间的结构差异。
