Crystal structure and functional characterization of Photosystem II-associated carbonic anhydrase CAH3 in Chlamydomonas reinhardtii
2015 (English)In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 167, no 3, 950-962 p.Article in journal (Refereed) Published
In oxygenic photosynthesis, light energy is stored in the form of chemical energy by converting CO2 and water into carbohydrates.The light-driven oxidation of water that provides the electrons and protons for the subsequent CO2 fixation takes place inphotosystem II (PSII). Recent studies show that in higher plants, HCO3– increases PSII activity by acting as a mobile acceptor ofthe protons produced by PSII. In the green alga Chlamydomonas reinhardtii, a luminal carbonic anhydrase, CrCAH3, was suggested toimprove proton removal from PSII, possibly by rapid reformation of HCO3– from CO2. In this study, we investigated the interplaybetween PSII and CrCAH3 by membrane inlet mass spectrometry and x-ray crystallography. Membrane inlet mass spectrometrymeasurements showed that CrCAH3 was most active at the slightly acidic pH values prevalent in the thylakoid lumen underillumination. Two crystal structures of CrCAH3 in complex with either acetazolamide or phosphate ions were determined at 2.6- and2.7-Å resolution, respectively. CrCAH3 is a dimer at pH 4.1 that is stabilized by swapping of the N-terminal arms, a feature notpreviously observed in a-type carbonic anhydrases. The structure contains a disulfide bond, and redox titration of CrCAH3 functionwith dithiothreitol suggested a possible redox regulation of the enzyme. The stimulating effect of CrCAH3 and CO2/HCO3– on PSIIactivity was demonstrated by comparing the flash-induced oxygen evolution pattern of wild-type and CrCAH3-less PSIIpreparations. We showed that CrCAH3 has unique structural features that allow this enzyme to maximize PSII activity at lowpH and CO2 concentration.
Place, publisher, year, edition, pages
American Society of Plant Biologists , 2015. Vol. 167, no 3, 950-962 p.
Botany Biochemistry and Molecular Biology
Research subject biological chemistry; Biochemistry
IdentifiersURN: urn:nbn:se:umu:diva-103651DOI: 10.1104/pp.114.253591ISI: 000354413900027OAI: oai:DiVA.org:umu-103651DiVA: diva2:814259
FunderKnut and Alice Wallenberg FoundationSwedish Research Council