Price G Dean, Maeda Shin-Ichi, Omata Tatsuo, Badger Murray R
Molecular Plant Physiology Group, Research School of Biological Sciences, Institute of Advanced Studies, The Australian National University, GPO Box 475, Canberra, ACT 2601, Australia.
Molecular Plant Physiology Group, Research School of Biological Sciences, Australian National University, PO Box 475, Canberra, ACT 0200, Australia.Molecular Plant Physiology Laboratory, Graduate School of BioAgricultural Science, Nagoya University, Nagoya, Japan (also Present address of SM).
Funct Plant Biol. 2002 Apr;29(3):131-149. doi: 10.1071/PP01229.
Cyanobacteria (blue-green algae) have evolved a remarkable environmental adaptation for survival at limiting CO2 concentrations. The adaptation is known as a CO2 concentrating mechanism, and functions to actively transport and accumulate inorganic carbon (Ci; HCO3 and CO2) within the cell. Thereafter, this Ci pool is utilised to provide elevated CO2 concentrations around the primary CO2 fixing enzyme, Rubisco, which is encapsulated in a unique micro-compartment known as the carboxysome. Recently, significant progress has been gained in understanding the different types of Ci transport in cyanobacteria. This semi-review centres on the model cyanobacterium, Synechococcus sp. PCC7942, which possesses at least four distinct modes of Ci uptake when grown under Ci limitation, each possessing a high degree of functional redundancy. The four modes so far identified are: (i) BCT1, an inducible, high affinity HCO3 transporter of the bacterial ATP binding cassette transporter family, encoded by cmpABCD; (ii) a constitutive, Na-dependent HCO3 transport system that can be allosterically activated (possibly by phosphorylation) in as little as 10 min; (iii) and (iv) two CO2 uptake systems, one constitutive and the other inducible, based on specialised forms of thylakoid-based, type 1, NAD(P)H dehydrogenase complexes (NDH-1). Here, we forward a speculative model that proposes that two unique proteins, ChpX and ChpY, possess CO2 hydration activity in the light, and when coupled to photosynthetic electron transport through the two specialised NDH-1 complexes, result in net hydration of CO2 to HCO3 as a crucial component of the CO2 uptake process.
蓝细菌（蓝绿藻）已经进化出一种显著的环境适应性机制，以便在二氧化碳浓度受限的情况下生存。这种适应性机制被称为二氧化碳浓缩机制，其功能是在细胞内主动运输和积累无机碳（Ci；碳酸氢根和二氧化碳）。此后，这个Ci库被用来在初级二氧化碳固定酶核酮糖-1,5-二磷酸羧化酶（Rubisco）周围提供升高的二氧化碳浓度，Rubisco被包裹在一个名为羧酶体的独特微区室中。最近，在理解蓝细菌中不同类型的Ci运输方面取得了重大进展。这篇半综述聚焦于模式蓝细菌聚球藻属PCC7942，当在Ci限制条件下生长时，它至少拥有四种不同的Ci摄取模式，每种模式都具有高度的功能冗余。到目前为止确定的四种模式是：（i）BCT1，一种由cmpABCD编码的、可诱导的、细菌ATP结合盒转运蛋白家族的高亲和力碳酸氢根转运蛋白；（ii）一种组成型的、依赖钠离子的碳酸氢根运输系统，该系统可在短短10分钟内被变构激活（可能通过磷酸化）；（iii）和（iv）两种二氧化碳摄取系统，一种是组成型的，另一种是可诱导的，基于类囊体膜上特殊形式的1型NAD(P)H脱氢酶复合物（NDH-1）。在此，我们提出一个推测性模型，该模型认为两种独特的蛋白质ChpX和ChpY在光照下具有二氧化碳水合活性，并且当通过两种特殊的NDH-1复合物与光合电子传递偶联时，会导致二氧化碳净水合形成碳酸氢根，这是二氧化碳摄取过程的一个关键组成部分。
