Identification and Structural Analysis of a Novel Carboxysome Shell Protein with Implications for Metabolite Transport
Identification and Structural Analysis of a Novel Carboxysome Shell Protein with Implications for Metabolite Transport
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DOI：
10.1016/j.jmb.2009.03.056
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发表时间：
2009-09-18
影响因子：
5.6
通讯作者：
Kerfeld, Cheryl A.
中科院分区：
文献类型：
--
作者：
Klein, Michael G.;Zwart, Peter;Kerfeld, Cheryl A.
细菌微区室（BMC）是完全由蛋白质组成的多面体，其在细菌中起细胞器的作用;它们通过包封和共定位靶向酶与其底物来促进亚细胞过程。最具特征的BMC是羧基体，这是碳浓缩机制的核心部分，大大增强了蓝藻和一些化能自养生物的碳固定。在这里，我们报告的第一个结构的见解原绿球藻，在世界上的贫营养海洋的数量占主导地位的蓝藻的羧基。生物信息学的方法，证实了基因表达数据的分析，被用来确定一个新的羧基体壳组件，CsoS 1D，在原绿球藻菌株MED 4的基因组中，直系同源随后在所有蓝藻中发现。原绿球藻MED 4 CsoS 1D的两个独立的晶体结构揭示了迄今为止在任何BMC结构域蛋白质结构中未发现的三个特征。首先，CsoS 1D由一对融合的BMC结构域组成。第二，这种双结构域蛋白三聚化形成一种新的假六聚体构建块，用于掺入到羧基体壳中，并且三聚体进一步二聚化，形成双层壳构建块。第三，最引人注目的是，在三重对称轴上形成的大孔似乎是门控的。三聚体的每个二聚体包含一个具有开放孔的三聚体和一个其孔由于在所有CsoS 1D直向同源物中不变的两个残基的侧链构象而被阻塞的三聚体。这是门控运输穿过羧基体壳的潜力的第一个证据，并揭示了BMC壳的新型构建块。(C)2009年由Elsevier Ltd.出版
Bacterial microcompartments (BMCs) are polyhedral bodies, composed entirely of proteins, that function as organelles in bacteria; they promote subcellular processes by encapsulating and co-localizing targeted enzymes with their substrates. The best-characterized BMC is the carboxysome, a central part of the carbon-concentrating mechanism that greatly enhances carbon fixation in cyanobacteria and some chemoautotrophs. Here we report the first structural insights into the carboxysome of Prochlorococcus, the numerically dominant cyanobacterium in the world's oligotrophic oceans. Bioinformatic methods, substantiated by analysis of gene expression data, were used to identify a new carboxysome shell component, CsoS1D, in the genome of Prochlorococcus strain MED4; orthologs were subsequently found in all cyanobacteria. Two independent crystal structures of Prochlorococcus MED4 CsoS1D reveal three features not seen in any BMC-domain protein structure solved to date. First, CsoS1D is composed of a fused pair of BMC domains. Second, this double-domain protein trimerizes to form a novel pseudohexameric building block for incorporation into the carboxysome shell, and the trimers further dimerize, forming a two-tiered shell building block. Third, and most strikingly, the large pore formed at the 3-fold axis of symmetry appears to be gated. Each dimer of trimers contains one trimer with an open pore and one whose pore is obstructed due to side-chain conformations of two residues that are invariant among all CsoS1D orthologs. This is the first evidence of the potential for gated transport across the carboxysome shell and reveals a new type of building block for BMC shells. (C) 2009 Published by Elsevier Ltd.