Allophycocyanin A is a carbon dioxide receptor in the cyanobacterial phycobilisome

Abstract

Light harvesting is fundamental for production of ATP and reducing equivalents for CO2 fixation during photosynthesis. However, electronic energy transfer (EET) through a photosystem can harm the photosynthetic apparatus when not balanced with CO2. Here, we show that CO2 binding to the light-harvesting complex modulates EET in photosynthetic cyanobacteria. More specifically, CO2 binding to the allophycocyanin alpha subunit of the light-harvesting complex regulates EET and its fluorescence quantum yield in the cyanobacterium Synechocystis sp. PCC 6803. CO2 binding decreases the inter-chromophore distance in the allophycocyanin trimer. The result is enhanced EET in vitro and in live cells. Our work identifies a direct target for CO2 in the cyanobacterial light-harvesting apparatus and provides insights into photosynthesis regulation.

A Non-Functional Carbon Dioxide-Mediated Post-Translational Modification on Nucleoside Diphosphate Kinase of Arabidopsis thaliana

“…This observation supports a hypothesis that CO 2 -lysine interactions will be widespread in a proteome. For example, approximately 50% of inorganic carbon in the photosynthetic protozoan Euglena gracilis was hypothesized to be in the form of protein carbamate [38] and a significant amount of CO 2 is protein-bound in Synechocystis and Arabidopsis, even when allowing for CO 2 bound to Rubisco [22,39]. Our observation of a non-functional carbamate PTM offers insight into a potential interpretation.…”

Near atmospheric carbon dioxide activates plant ubiquitin cross-linking

“…1 A) was initially discovered as a PTM regulating Rubisco [22] and haemoglobin [22] activities. It has subsequently been observed on mammalian ubiquitin [18] , cyanobacterial allophycocyanin A [23] and PII protein [19] . Furthermore, a subset of proteins has a locally stabilised carbamate PTM typically utilised for catalysis.…”

“…Studies in prokaryotes [ 19 , 23 , 26 ] and plants [27] demonstrate multiple proteins that bind CO 2 through carbamate formation. Therefore, while the identification of MPK4/12 and HT1 as a CO 2 sensing module that converges on CBC1 kinase in CO 2 -regulated stomatal movements [21] represents a significant advance, it is likely that overall plant physiology responds to CO 2 by a variety of mechanisms.…”

Inorganic carbon sensing and signalling in cyanobacteria

“…However, molecular mechanisms regulating growth and photosynthesis according to available Ci are less well understood. A direct link between CO 2 and photosynthetic light harvesting was recently discovered as CO 2 was shown to be bound to the α subunit of allophycocyanin, causing a structural change that enhances the energy transfer efficiency within the phycobilisome (Guillén‐García et al 2022). Furthermore, Photosystem II activity is influenced by two bicarbonate molecules that bind to the acceptor and donor sides of Photosystem II (Shevala et al 2020) and might provide a direct link to how scarcity of inorganic carbon could regulate light reactions.…”