Marx Ailie, Adir Noam
Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa, Israel.
Biochim Biophys Acta. 2013 Mar;1827(3):311-8. doi: 10.1016/j.bbabio.2012.11.006. Epub 2012 Nov 28.
X-ray crystal structures of the isolated phycobiliprotein components of the phycobilisome have provided high resolution details to the description of this light harvesting complex at different levels of complexity and detail. The linker-independent assembly of trimers into hexamers in crystal lattices of previously determined structures has been observed in almost all of the phycocyanin (PC) and allophycocyanin (APC) structures available in the Protein Data Bank. In this paper we describe the X-ray crystal structures of PC and APC from Synechococcus elongatus sp. PCC 7942, PC from Synechocystis sp. PCC 6803 and PC from Thermosynechococcus vulcanus crystallized in the presence of urea. All five structures are highly similar to other PC and APC structures on the levels of subunits, monomers and trimers. The Synechococcus APC forms a unique loose hexamer that may show the structural requirements for core assembly and rod attachment. While the Synechococcus PC assembles into the canonical hexamer, it does not further assemble into rods. Unlike most PC structures, the Synechocystis PC fails to form hexamers. Addition of low concentrations of urea to T. vulcanus PC inhibits this proteins propensity to form hexamers, resulting in a crystal lattice composed of trimers. The molecular source of these differences in assembly and their relevance to the phycobilisome structure is discussed.
藻胆体中分离出的藻胆蛋白组分的X射线晶体结构，为描述这种不同复杂程度和细节水平的光捕获复合物提供了高分辨率的细节信息。在蛋白质数据库中几乎所有已确定结构的藻蓝蛋白（PC）和别藻蓝蛋白（APC）结构中，都观察到三聚体在晶格中不依赖连接蛋白组装成六聚体的现象。在本文中，我们描述了来自聚球藻属嗜热栖热菌PCC 7942的PC和APC、来自集胞藻属PCC 6803的PC以及在尿素存在下结晶的嗜热栖热菌PC的X射线晶体结构。所有这五种结构在亚基、单体和三聚体水平上都与其他PC和APC结构高度相似。聚球藻属的APC形成一种独特的松散六聚体，这可能显示了核心组装和棒状附着的结构要求。虽然聚球藻属的PC组装成典型的六聚体，但它不会进一步组装成棒状结构。与大多数PC结构不同，集胞藻属的PC无法形成六聚体。向嗜热栖热菌PC中添加低浓度的尿素会抑制该蛋白形成六聚体的倾向，从而形成由三聚体组成的晶格。本文讨论了这些组装差异的分子来源及其与藻胆体结构的相关性。
