Probing the rice Rubisco-Rubisco activase interaction via subunit heterooligomerization

Area of Science:

• Plant Biochemistry
• Molecular Biology
• Photosynthesis Research

Background:

• Rubisco activase (Rca) is an AAA+ protein and molecular chaperone essential for photosynthesis.
• Rca remodels inhibited active sites of Rubisco (ribulose 1,5-bisphosphate carboxylase/oxygenase) to maintain CO2 fixation.
• Understanding Rca's mechanism is critical for crop improvement, as it regulates a rate-limiting step in photosynthesis.

Purpose of the Study:

• To elucidate the mechanism of rice Rubisco activase (Rca) by probing its Rubisco-interacting surface.
• To identify key residues involved in the interaction between Rca and Rubisco.
• To understand how Rca's hexameric structure influences its function in regulating photosynthesis.

Main Methods:

• Structure-guided mutagenesis was employed to create mutant rice Rca proteins.
• Mutant Rca proteins were analyzed for uncoupled ATPase and Rca activity.
• Mutant doping experiments evaluated the importance of Rubisco-interacting residues within the Rca hexamer.

Main Results:

• Mutations in Ser-23, Lys-148, and Arg-321 disrupted the coupling of ATPase and Rca activity, suggesting their role in Rubisco interaction.
• Rca hexamers with subunits lacking the N-terminal Rubisco-interacting domain showed a twofold increase in Rca function.
• Rubisco-interacting residues at the hexamer's rim were less critical for Rca function compared to those near the axial pore.

Conclusions:

• Specific residues on the Rca surface are critical for its interaction with Rubisco.
• The spatial arrangement of Rubisco-interacting residues within the Rca hexamer impacts its regulatory function.
• This detailed functional understanding of Rca can guide strategies for enhancing crop photosynthesis, growth, and yield.