The reaction centre-light harvesting 1 (RC-LH1) core complex is indispensable for anoxygenic photosynthesis. In the purple bacterium Rhodobacter (Rba.) sphaeroides RC-LH1 is produced both as a monomer, in which 14 LH1 subunits form a C-shaped antenna around 1 RC, and as a dimer, where 28 LH1 subunits form an S-shaped antenna surrounding 2 RCs. Alongside the five RC and LH1 subunits, an additional polypeptide known as PufX provides an interface for dimerisation and also prevents LH1 ring closure, introducing a channel for quinone exchange that is essential for photoheterotrophic growth. Structures of Rba. sphaeroides RC-LH1 complexes revealed several new components; protein-Y, which helps to form the quinone channel; protein-Z, of unknown function and seemingly unique to dimers; and a tightly bound sulfoquinovosyl diacylglycerol (SQDG) lipid that interacts with two PufX arginine residues. This lipid lies at the dimer interface alongside weak density for a second molecule, previously proposed to be an ornithine lipid. In this work we have generated strains of Rba. sphaeroides lacking protein-Y, protein-Z, SQDG or ornithine lipids to assess the roles of these previously unknown components in the assembly and activity of RC-LH1. We show that whilst the removal of either protein-Y, protein-Z or ornithine lipids has only subtle effects, SQDG is essential for the formation of RC-LH1 dimers but its absence has no functional effect on the monomeric complex.

中文翻译：

---

磺基喹诺酰二酰基甘油是球形红杆菌反应中心光收集 1 核心复合物二聚化所必需的


反应中心光捕获 1 (RC-LH1) 核心复合物对于无氧光合作用是不可或缺的。在紫色细菌球形红杆菌 (Rba.) 中，RC-LH1 既可以作为单体产生，其中 14 个 LH1 亚基在 1 RC 周围形成 C 形天线，也可以作为二聚体产生，其中 28 个 LH1 亚基形成 S 形天线周围有2个RC。除了五个 RC 和 LH1 亚基之外，一种称为 PufX 的附加多肽提供了二聚化界面，并防止 LH1 环闭合，引入了对光异养生长至关重要的醌交换通道。 Rba 的结构。 sphaeroides RC-LH1 复合物揭示了几种新成分； Y蛋白，有助于形成醌通道；蛋白质-Z，功能未知，似乎是二聚体所独有的；以及紧密结合的磺基喹诺酰二酰基甘油 (SQDG) 脂质，可与两个 PufX 精氨酸残基相互作用。这种脂质位于二聚体界面，旁边是第二个分子的弱密度，先前被认为是鸟氨酸脂质。在这项工作中，我们产生了 Rba 菌株。缺乏蛋白质 Y、蛋白质 Z、SQDG 或鸟氨酸脂质的球状体，以评估这些先前未知的成分在 RC-LH1 组装和活性中的作用。我们表明，虽然去除蛋白质-Y、蛋白质-Z 或鸟氨酸脂质只会产生微妙的影响，但 SQDG 对于 RC-LH1 二聚体的形成至关重要，但它的缺失对单体复合物没有功能影响。