Sutter Markus, Roberts Evan W, Gonzalez Raul C, Bates Cassandra, Dawoud Salma, Landry Kimberly, Cannon Gordon C, Heinhorst Sabine, Kerfeld Cheryl A
MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA.
Physical Biosciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA.
Sci Rep. 2015 Nov 5;5:16243. doi: 10.1038/srep16243.
Carboxysomes are bacterial microcompartments that enhance carbon fixation by concentrating ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and its substrate CO2 within a proteinaceous shell. They are found in all cyanobacteria, some purple photoautotrophs and many chemoautotrophic bacteria. Carboxysomes consist of a protein shell that encapsulates several hundred molecules of RuBisCO, and contain carbonic anhydrase and other accessory proteins. Genes coding for carboxysome shell components and the encapsulated proteins are typically found together in an operon. The α-carboxysome operon is embedded in a cluster of additional, conserved genes that are presumably related to its function. In many chemoautotrophs, products of the expanded carboxysome locus include CbbO and CbbQ, a member of the AAA+ domain superfamily. We bioinformatically identified subtypes of CbbQ proteins and show that their genes frequently co-occur with both Form IA and Form II RuBisCO. The α-carboxysome-associated ortholog, CsoCbbQ, from Halothiobacillus neapolitanus forms a hexamer in solution and hydrolyzes ATP. The crystal structure shows that CsoCbbQ is a hexamer of the typical AAA+ domain; the additional C-terminal domain, diagnostic of the CbbQ subfamily, structurally fills the inter-monomer gaps, resulting in a distinctly hexagonal shape. We show that CsoCbbQ interacts with CsoCbbO and is a component of the carboxysome shell, the first example of ATPase activity associated with a bacterial microcompartment.
羧酶体是细菌微区室，通过在蛋白质外壳内浓缩1,5-二磷酸核酮糖羧化酶/加氧酶（RuBisCO）及其底物CO₂来增强碳固定。它们存在于所有蓝细菌、一些紫色光合自养生物和许多化能自养细菌中。羧酶体由包裹数百个RuBisCO分子的蛋白质外壳组成，并含有碳酸酐酶和其他辅助蛋白。编码羧酶体外壳成分和被包裹蛋白的基因通常一起存在于一个操纵子中。α-羧酶体操纵子嵌入在一组可能与其功能相关的其他保守基因簇中。在许多化能自养生物中，扩展的羧酶体位点的产物包括CbbO和CbbQ，后者是AAA + 结构域超家族的成员。我们通过生物信息学方法鉴定了CbbQ蛋白的亚型，并表明它们的基因经常与I型和II型RuBisCO同时出现。来自那不勒斯嗜盐硫杆菌的与α-羧酶体相关的直系同源物CsoCbbQ在溶液中形成六聚体并水解ATP。晶体结构表明，CsoCbbQ是典型AAA + 结构域的六聚体；额外的C末端结构域是CbbQ亚家族的诊断结构域，在结构上填充了单体间的间隙，形成了明显的六边形形状。我们表明，CsoCbbQ与CsoCbbO相互作用，是羧酶体外壳的一个组成部分，这是与细菌微区室相关的ATP酶活性的第一个例子。
