In-cell Structure and Variability of Pyrenoid Rubisco

Area of Science:

• Biochemistry
• Structural Biology
• Photosynthesis Research

Background:

• Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is crucial for CO2 fixation but has low catalytic efficiency.
• CO2-concentrating mechanisms, including the pyrenoid in algae, enhance Rubisco's efficiency.
• Previous Rubisco structure studies used in vitro methods, leaving its native state elusive.

Purpose of the Study:

• To investigate the native structure and dynamics of Rubisco within the pyrenoid of Chlamydomonas reinhardtii.
• To understand Rubisco's functional organization and interactions within its native environment.
• To determine the activated conformation of Rubisco in vivo.

Main Methods:

• Cryo-focused ion beam (cryo-FIB) milling of Chlamydomonas reinhardtii cells.
• Cryo-electron tomography (cryo-ET) for high-resolution imaging of cellular structures.
• Subtomogram averaging and 3D classification for structural reconstruction.

Main Results:

• Sub-nanometer resolution reconstruction of native pyrenoid Rubisco.
• Determination of a closed, activated Rubisco conformation.
• Identification of local structural variations and associations with binding proteins within the pyrenoid.

Conclusions:

• Provides a comprehensive structural description of Rubisco in its native pyrenoid environment.
• Offers insights into Rubisco dynamics and functional organization.
• Enhances understanding of CO2 fixation mechanisms in algae.