Protein subunit

Neuroscience

Enzyme

Ribulose 1,5-bisphosphate

RNA-dependent RNA polymerase

RuBisCO

Carbon dioxide

Evolutionary biology

Biology

Gene

Specificity factor

Pyruvate carboxylase

Catalysis

Oxygenase

Adaptation (eye)

Photosynthesis

Ecology

Carboxylation

Substrate (aquarium)

Substrate specificity

Ribulose

Botany

Biochemistry

Science

The evolution of ribulose-1,5-bisphosphate carboxylase/oxygenases (Rubiscos) that discriminate strongly between their substrate carbon dioxide and the undesired side substrate dioxygen was an important event for photosynthetic organisms adapting to an oxygenated environment. We use ancestral sequence reconstruction to recapitulate this event. We show that Rubisco increased its specificity and carboxylation efficiency through the gain of an accessory subunit before atmospheric oxygen was present. Using structural and biochemical approaches, we retrace how this subunit was gained and became essential. Our work illuminates the emergence of an adaptation to rising ambient oxygen levels, provides a template for investigating the function of interactions that have remained elusive because of their essentiality, and sheds light on the determinants of specificity in Rubisco.

Evolution of increased complexity and specificity at the dawn of form I Rubiscos