Asymmetric functional interaction between chaperonin and its plastidic cofactors

Area of Science:

• Molecular Biology
• Protein Folding
• Chaperone Proteins

Background:

• Chloroplast chaperonin (Cpn)20, with two GroES-like domains, is abundant in plant and algal chloroplasts.
• The cooperation mechanism between Cpn20 oligomers and chaperonins, despite symmetry mismatches, remains unclear.

Purpose of the Study:

• To characterize the functional cooperation of plastidic Cpn20 homo-oligomers and CrCPNs hetero-oligomer with chaperonins GroEL and CrCPN60.
• To investigate the role of symmetry in chaperonin-cochaperonin interactions.

Main Methods:

• Functional assays using Arabidopsis (AtCpn20) and Chlamydomonas (CrCPN20, CrCPNs) cochaperonins.
• In vitro refolding of Rhodospirillum rubrum ribulose bisphosphate carboxylase oxygenase (RrRubisco) with Escherichia coli GroEL and Chlamydomonas CrCPN60 chaperonins.
• Complementation assays in GroES-deficient E. coli.

Main Results:

• AtCpn20 and CrCPNs functionally assisted both GroEL and CrCPN60 in RrRubisco refolding and complemented GroES function.
• CrCPN20 selectively cooperated with CrCPN60, not GroEL, for RrRubisco refolding and showed differential complementation in E. coli.
• Cochaperonin concatamers exhibited similar function to their native forms.

Conclusions:

• Symmetrical match between chaperonin and cochaperonin is not essential for functional cooperation.
• Cochaperonins exhibit specificity in their interactions with different chaperonins.