Abstract
BackgroundChloroplast chaperonin, consisting of multiple subunits, mediates folding of the highly abundant protein Rubisco with the assistance of co-chaperonins. ATP hydrolysis drives the chaperonin allosteric cycle to assist substrate folding and promotes disassembly of chloroplast chaperonin. The ways in which the subunits cooperate during this cycle remain unclear.ResultsHere, we report the first crystal structure of Chlamydomonas chloroplast chaperonin homo-oligomer (CPN60β1) at 3.8 Å, which shares structural topology with typical type I chaperonins but with looser compaction, and possesses a larger central cavity, less contact sites and an enlarged ATP binding pocket compared to GroEL. The overall structure of Cpn60 resembles the GroEL allosteric intermediate state. Moreover, two amino acid (aa) residues (G153, G154) conserved among Cpn60s are involved in ATPase activity regulated by co-chaperonins. Domain swapping analysis revealed that the monomeric state of CPN60α is controlled by its equatorial domain. Furthermore, the C-terminal segment (aa 484–547) of CPN60β influenced oligomer disassembly and allosteric rearrangement driven by ATP hydrolysis. The entire equatorial domain and at least one part of the intermediate domain from CPN60α are indispensable for functional cooperation with CPN60β1, and this functional cooperation is strictly dependent on a conserved aa residue (E461) in the CPN60α subunit.ConclusionsThe first crystal structure of Chlamydomonas chloroplast chaperonin homo-oligomer (CPN60β1) is reported. The equatorial domain maintained the monomeric state of CPN60α and the C-terminus of CPN60β affected oligomer disassembly driven by ATP. The cooperative roles of CPN60 subunits were also established.Electronic supplementary materialThe online version of this article (doi:10.1186/s12915-016-0251-8) contains supplementary material, which is available to authorized users.
Highlights
Chloroplast chaperonin, consisting of multiple subunits, mediates folding of the highly abundant protein Rubisco with the assistance of co-chaperonins
Homo-oligomeric CPN60β1 bound to co-chaperonins but could not assist folding of model substrate RrRubisco In Chlamydomonas, functional CPN60 is composed of three subunits [39]
Both GroES and CPN20 from Chlamydomonas (CrCPN20) could form complexes with homo-oligomeric CPN60β1 (Fig. 1a). Both ‘bullet’ and ‘football’ structures were observed by electron microscopy after incubation of CPN60β1 with GroES in the presence of ATPAlF3, with ‘football’ structures being prevalent (Fig. 1b) [22, 24]. These results indicate that CPN60β1 interacted with co-chaperonins
Summary
Chloroplast chaperonin, consisting of multiple subunits, mediates folding of the highly abundant protein Rubisco with the assistance of co-chaperonins. Group II chaperonins are further divided into archaeal types (thermosome) and eukaryotic types (TRiC) [8, 9]. Both chaperonin groups share a similar molecular architecture consisting of two back-to-back stacked rings, with a central cavity in each ring that. The equatorial domain (aa residues 2–136 and 410–525) contains the ATP binding site and contributes to inter-ring contacts [19]. These two domains are connected by the intermediate hinge domain (aa residues 137–188 and 378–409), which allows rigid body movement
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call