Stability-activity tradeoffs constrain the adaptive evolution of RubisCO

Area of Science:

• Biochemistry
• Evolutionary Biology
• Plant Science

Background:

• Ribulose-1,5-bisphosphate carboxylase (RubisCO) is key to CO2 fixation in photosynthesis.
• Most plants use the C3 pathway, but C4 photosynthesis evolved convergently in flowering plants.
• C4 RubisCO exhibits altered CO2 specificity and faster turnover due to specific mutations.

Purpose of the Study:

• To investigate the physical constraints and evolutionary trajectory of RubisCO during the C3 to C4 transition.
• To understand the role of enzyme stability and activity tradeoffs in adaptation.
• To identify specific mutations and their structural impact on RubisCO function.

Main Methods:

• In silico reconstruction of ancestral RubisCO sequences and 3D structures from C3 and C4 species.
• Phylogenetic analysis to track evolutionary changes and identify mutations.
• Evaluation of mutation effects on enzyme stability and inferred functional impact.

Main Results:

• RubisCO evolution is constrained by stability-activity tradeoffs, mirroring laboratory findings.
• C4 RubisCO properties arise from destabilizing mutations enhancing catalytic cycle flexibility.
• These mutations are located near, but not within, the active site or intersubunit interfaces.
• Increased enzyme stability preceded C4 adaptation, followed by compensatory mutations.

Conclusions:

• The evolution of C4 photosynthesis in RubisCO involved a period of enhanced stability enabling subsequent destabilizing mutations.
• These mutations near the active site improve conformational flexibility, optimizing CO2 fixation.
• Understanding these evolutionary constraints provides insight into enzyme adaptation mechanisms.