Structures of cyanobacterial bicarbonate transporter SbtA and its complex with PII-like SbtB
Xiaoyu Liu, Wen‐Tao Hou, Liang Wang, Bo Li, Yu Chen, Yuxing Chen, Yong‐Liang Jiang, Cong‐Zhao Zhou, Yong‐Liang Jiang, Cong‐Zhao Zhou
Abstract
Carbon and nitrogen, the uptake and intracellular metabolisms of which are tightly coupled 1 , are the two most fundamental nutrients for all living organisms. As one of the most ancient autotrophic bacteria, cyanobacteria utilize photosynthesis to convert the inorganic carbon (C i ) into carbohydrates. Carbon fixation is catalyzed by ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), which is a naturally inefficient enzyme 2 . In response to gradually decreased CO 2 and elevated O 2 levels in the atmosphere, cyanobacteria have evolved a unique CO 2 -concentrating mechanism (CCM), which can substantially accumulate CO 2 in the vicinity of RuBisCO for improved carboxylation efficiency 3 . The cyanobacterial CCM consists of a subcellular self-assembled icosahedral microcompartment, termed the carboxysome, and several C i uptake systems 3 . To date, five C i -uptake systems have been identified in cyanobacteria, including three bicarbonate transporters BicA, SbtA, and BCT1, in addition to two CO 2 -uptake complexes: NDH-I 3 and NDH-I 4 .