In-cell structure and variability of pyrenoid Rubisco

Area of Science:

• Structural Biology
• Biochemistry
• Algal Biology

Background:

• Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is crucial for global carbon dioxide (CO2) fixation.
• In eukaryotic algae, the pyrenoid organelle concentrates CO2 to enhance Rubisco's catalytic efficiency.
• The in vitro structure of Rubisco is well-understood, but its native state within the pyrenoid is largely unknown.

Purpose of the Study:

• To determine the native structure and dynamics of Rubisco within the pyrenoid of Chlamydomonas reinhardtii.
• To investigate the structural variations and interactions of Rubisco in its natural cellular environment.
• To gain insights into the functional organization of Rubisco for improved CO2 fixation.

Main Methods:

• Cryo-electron tomography was employed to image cells.
• Cryo-focused ion beam milling was used for sample preparation.
• Subtomogram averaging was applied to reconstruct the native Rubisco structure.

Main Results:

• Multiple structural subsets of Rubisco were identified within the pyrenoid.
• Rubisco was observed in an active conformation in the highest-resolution map.
• Significant local variations were found at the active site, dimer interfaces, and binding protein contact regions.

Conclusions:

• This study provides a comprehensive understanding of native Rubisco structure and dynamics within the algal pyrenoid.
• The findings reveal local structural heterogeneity of Rubisco, impacting its function.
• Insights into Rubisco's organization offer valuable perspectives on enhancing CO2 fixation.