Small subunit isoform diversity underlies structural heterogeneity in native plant Rubisco

Area of Science:

• Plant biology
• Molecular and structural biology
• Biochemistry

Background:

• Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is crucial for CO2 fixation in photosynthesis and is the most abundant protein on Earth.
• In plants, Rubisco forms a hexadecameric L8S8 complex, with large subunits (LSu) encoded by chloroplast DNA and small subunits (SSu) encoded by nuclear genes, leading to diverse SSu isoforms.
• Previous research lacked structural evidence for the co-assembly of different SSu isoforms within individual Rubisco holoenzymes.

Purpose of the Study:

• To investigate the structural heterogeneity of Rubisco small subunits (SSu) in terrestrial plants.
• To determine if multiple SSu isoforms can co-assemble within a single Rubisco holoenzyme complex.
• To elucidate the structural basis and composition of these mixed-isoform Rubisco complexes.

Main Methods:

• Purification of native Rubisco from Arabidopsis thaliana.
• Application of high-resolution mass spectrometry to identify complex composition.
• Utilizing cryo-electron microscopy for near-atomic resolution structural analysis.

Main Results:

• Demonstrated that multiple SSu isoforms can co-assemble within individual Rubisco holoenzyme complexes.
• Unambiguously identified the composition of these mixed-isoform Rubisco complexes.
• Elucidated isoform-specific structural interactions at near-atomic resolution.

Conclusions:

• Established structural heterogeneity in plant Rubisco due to SSu isoform co-assembly.
• This finding provides a structural basis for understanding the functional plasticity of Rubisco.
• Future research can now explore the impact of SSu diversity on Rubisco kinetics and function under varying environmental conditions.