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Carbon fixation, the conversion of inorganic carbon to organic matter, is arguably the most fundamental biological process sustaining life on Earth. Approximately 100 gigatons (Gt) of carbon is estimated to be fixed by autotropic organisms each year. This is equivalent to 4×10^18 kilojoules (kJ) of energy per year, 37 times more than world’s annual electricity consumption. Despite this immense productivity, carbon fixation is nearly impossible in modern environments without specialized biological adaptations. This is primarily due to the limited supply of environmental carbon dioxide (CO2) and oxygen (O2) inhibition of the key enzyme, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) in the Calvin–Benson–Bassham cycle. To survive against these challenges, many autotrophs evolved sophisticated Carbon-Concentrating Mechanisms (CCMs), a diversity of biophysical and biochemical adaptations that allow them to accumulate an extreme concentration of intracellular inorganic carbon 1,000-folds above the environmental supply.
CCMs can be found across all three domains of life, in which the types of CCMs autotrophs utilize is catered to their local habitats. Aquatic organisms, such as cyanobacteria and algae possess various active uptake systems that directly transport inorganic carbon or indirectly facilitate its diffusion into the cell. Additionally, autotrophic bacteria also make use of cellular microcompartments to protect enzymes from oxygen inhibition and trap CO2 in vicinity. Meanwhile, some higher plants developed specialized metabolisms to concentrate intracellular CO2 or coordinate carbon fixation under the optimal conditions. Despite countless research since the first discovery of CCMs, the molecular mechanisms of active inorganic carbon uptake systems remain largely enigmatic, in particular among chemoautotrophs, bacteria that utilize chemical energy to fix inorganic carbon. This thesis aims to narrow this gap by exploring the structures and mechanisms of two CO2 uptake systems, namely the NDH-1MS’ complex and the recently identified DIC-CT system. The former system is exclusively employed by cyanobacteria, while the latter is utilized by various chemoautotrophs, and surprisingly can also be found in some heterotrophic bacteria. These unrelated systems represent two unique solutions to the same biological problem.
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Issued: 2025-12-15
Faculty
FB15:Chemie
Language
en
Keywords
Biochemistry
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Lo, Yat Kei: Structure and Mechanism of Prokaryotic Carbon-Concentrating Mechanisms. : 2025-12-15.
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