The role of carbon dioxide in allophycocyanin biochemistry

Abstract

Carbon dioxide (CO2) plays an essential role in fundamental biological processes such as respiration and photosynthesis. The ability of cyanobacteria to use water as an electron source in photosynthesis contributes to the balance between CO2 and O2 in the atmosphere. However, the molecular mechanisms by which cyanobacteria directly detect environmental CO2 are still unknown. Such knowledge could enhance opportunities for engineering cyanobacterial carbon responses in green biotechnology. CO2 can react with neutral amines at physiological temperatures and pressures to form carbamates. This post-translational modification has been reported on RuBisCO and haemoglobin but is unexplored as a mechanism for CO2 detection in cyanobacteria. This thesis identifies the carbamylation of a light-harvesting protein in the photosynthetic cyanobacterium Synechocystis sp. PCC 6803. This research presents work on the discovery of previously unknown carbamate formation,
as well as spectroscopic analysis of the CO2-binding role in energy transfer. Carbamate formation was identified using ESI-MS/MS combined with 12C and
13C isotope addition. The proteomic screen was validated by the study of recombinant proteins using 13C NMR. CO2-binding to the Synechocystis sp. PCC 6803 light-harvesting protein proved to affect excitation energy transfer. This thesis provides evidence of a novel area of research on the effects of CO2 in the light-harvesting complex energy transfer.