Insights from multiple structures of the shell proteins from the β‐carboxysome
Insights from multiple structures of the shell proteins from the β‐carboxysome
复制标题
来自 β-羧基体的壳蛋白的多种结构的见解
作者：
Shiho Tanaka;M. Sawaya;M. Phillips;T. Yeates
碳体是原始的细菌细胞器，在无机碳有限的条件下作为碳浓缩机制（CCM）的一部分发挥作用。羧基体通过将碳酸酐酶和CO2固定酶核酮糖-1，5-二磷酸羧化酶/加氧酶（RuBisCO）包封在一起来提高细胞碳固定的效率。羧基体具有大致二十面体的形状，外壳直径在800和1500 μ m之间，其由几千个小蛋白质亚基构成。在蓝细菌集胞藻PCC 6803中，先前对两个同源壳蛋白亚基CcmK 2和CcmK 4的结构测定阐明了外壳是如何通过CcmK六聚体紧密包装成分子层而形成的。在这里，我们描述了六聚体壳蛋白CcmK 1的晶体结构，沿着CcmK 1和CcmK 2的突变体的结构，它们有时缺乏灵活的C末端尾部。注意到六聚体包装成层的方式的变化，而硫酸根离子通过层结合在孔中提供了进一步的支持的假设，即孔用于运输底物和产物进出羧基体。其中一种新结构为随后通过孔的分子输运的计算研究提供了高分辨率（1.3 μ m）框架。C末端缺失突变体的晶体和溶液研究表明，末端片段参与蛋白质-蛋白质相互作用的趋势，从而提供了六聚体壳蛋白分子层的哪一侧可能面向羧基体内部的线索。
Carboxysomes are primitive bacterial organelles that function as a part of a carbon concentrating mechanism (CCM) under conditions where inorganic carbon is limiting. The carboxysome enhances the efficiency of cellular carbon fixation by encapsulating together carbonic anhydrase and the CO2‐fixing enzyme ribulose‐1,5‐bisphosphate carboxylase/oxygenase (RuBisCO). The carboxysome has a roughly icosahedral shape with an outer shell between 800 and 1500 Å in diameter, which is constructed from a few thousand small protein subunits. In the cyanobacterium Synechocystis sp. PCC 6803, the previous structure determination of two homologous shell protein subunits, CcmK2 and CcmK4, elucidated how the outer shell is formed by the tight packing of CcmK hexamers into a molecular layer. Here we describe the crystal structure of the hexameric shell protein CcmK1, along with structures of mutants of both CcmK1 and CcmK2 lacking their sometimes flexible C‐terminal tails. Variations in the way hexamers pack into layers are noted, while sulfate ions bound in pores through the layer provide further support for the hypothesis that the pores serve for transport of substrates and products into and out of the carboxysome. One of the new structures provides a high‐resolution (1.3 Å) framework for subsequent computational studies of molecular transport through the pores. Crystal and solution studies of the C‐terminal deletion mutants demonstrate the tendency of the terminal segments to participate in proteinprotein interactions, thereby providing a clue as to which side of the molecular layer of hexameric shell proteins is likely to face toward the carboxysome interior.
DOI：
10.1016/j.str.2008.05.013
发表时间：
2008-09-10
期刊：
Structure (London, England : 1993)
影响因子：
--
作者：
Crowley CS;Sawaya MR;Bobik TA;Yeates TO
通讯作者：
Yeates TO
影响因子：
5.6
作者：
Schmid, Michael F.;Paredes, Angel M.;Shively, Jessup M.
通讯作者：
Shively, Jessup M.