Premium
A thylakoid‐located carbonic anhydrase regulates CO 2 uptake in the cyanobacterium Synechocystis sp. PCC 6803
Author(s) -
Sun Nan,
Han Xunling,
Xu Min,
Kaplan Aaron,
Espie George S.,
Mi Hualing
Publication year - 2019
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.15575
Subject(s) - thylakoid , photosynthesis , carbonic anhydrase , synechocystis , bicarbonate , photoinhibition , cyanobacteria , biophysics , extracellular , biochemistry , chemistry , electron transport chain , chloroplast , rubisco , photosystem ii , carbon fixation , biology , enzyme , bacteria , genetics , organic chemistry , mutant , gene
Summary Carbonic anhydrases ( CA s) are involved in CO 2 uptake and conversion, a fundamental process in photosynthetic organisms. Nevertheless, the mechanism underlying the regulation of CO 2 uptake and intracellular conversion in cyanobacteria is largely unknown. We report the characterization of a previously unrecognized thylakoid‐located CA Slr0051 (EcaB) from the cyanobacterium Synechocystis sp. PCC 6803, which possesses CA activity to regulate CO 2 uptake. Inactivation of ecaB stimulated CO 2 hydration in the thylakoids, suppressed by the classical CA inhibitor acetazolamide. Absence of ecaB increased the reduced state of the photosynthetic electron transport system, lowered the rate of photosynthetic O 2 evolution at high light ( HL ) and pH , and decreased the cellular affinity for extracellular inorganic carbon. Furthermore, EcaB was upregulated in cells grown at limiting CO 2 concentration or HL in tandem with CupA. EcaB is mainly located in the thylakoid membranes where it interacts with CupA and CupB involved in CO 2 uptake by converting it to bicarbonate. We propose that modulation of the EcaB level and activity in response to CO 2 changes, illumination or pH reversibly regulates its conversion to HCO 3 by the two CO 2 ‐uptake systems (CupA, CupB), dissipating the excess HCO 3 − and alleviating photoinhibition, and thereby optimizes photosynthesis, especially under HL and alkaline conditions.