Dangel Andrew W, Tabita F Robert
Department of Microbiology, The Ohio State University, Columbus, Ohio, USA.
Department of Microbiology, The Ohio State University, Columbus, Ohio, USA
J Bacteriol. 2015 Nov;197(22):3488-98. doi: 10.1128/JB.00442-15. Epub 2015 Aug 31.
Biological carbon dioxide fixation is an essential and crucial process catalyzed by both prokaryotic and eukaryotic organisms to allow ubiquitous atmospheric CO2 to be reduced to usable forms of organic carbon. This process, especially the Calvin-Bassham-Benson (CBB) pathway of CO2 fixation, provides the bulk of organic carbon found on earth. The enzyme ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase (RubisCO) performs the key and rate-limiting step whereby CO2 is reduced and incorporated into a precursor organic metabolite. This is a highly regulated process in diverse organisms, with the expression of genes that comprise the CBB pathway (the cbb genes), including RubisCO, specifically controlled by the master transcriptional regulator protein CbbR. Many organisms have two or more cbb operons that either are regulated by a single CbbR or employ a specific CbbR for each cbb operon. CbbR family members are versatile and accommodate and bind many different effector metabolites that influence CbbR's ability to control cbb transcription. Moreover, two members of the CbbR family are further posttranslationally modified via interactions with other transcriptional regulator proteins from two-component regulatory systems, thus augmenting CbbR-dependent control and optimizing expression of specific cbb operons. In addition to interactions with small effector metabolites and other regulator proteins, CbbR proteins may be selected that are constitutively active and, in some instances, elevate the level of cbb expression relative to wild-type CbbR. Optimizing CbbR-dependent control is an important consideration for potentially using microbes to convert CO2 to useful bioproducts.
生物二氧化碳固定是原核生物和真核生物催化的一个必不可少且至关重要的过程，它能使无处不在的大气中的二氧化碳被还原为可利用的有机碳形式。这个过程，尤其是二氧化碳固定的卡尔文-巴斯姆-本森（CBB）途径，提供了地球上发现的大部分有机碳。1,5-二磷酸核酮糖（RuBP）羧化酶/加氧酶（RubisCO）执行关键的限速步骤，在此步骤中二氧化碳被还原并整合到一种前体有机代谢物中。在多种生物体中，这是一个高度受调控的过程，组成CBB途径的基因（cbb基因）的表达，包括RubisCO，由主转录调节蛋白CbbR特异性控制。许多生物体有两个或更多的cbb操纵子，它们要么由单个CbbR调控，要么每个cbb操纵子采用特定的CbbR。CbbR家族成员具有多样性，能容纳并结合许多不同的效应代谢物，这些代谢物会影响CbbR控制cbb转录的能力。此外，CbbR家族的两个成员通过与双组分调节系统中的其他转录调节蛋白相互作用，进一步进行翻译后修饰，从而增强CbbR依赖性控制并优化特定cbb操纵子的表达。除了与小效应代谢物和其他调节蛋白相互作用外，还可以选择组成型激活的CbbR蛋白，在某些情况下，相对于野生型CbbR，它们能提高cbb的表达水平。优化CbbR依赖性控制是潜在利用微生物将二氧化碳转化为有用生物产品的一个重要考虑因素。
