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TitleAncestral Chaperonins Provide the First Structural Glimpse into Early Multimeric Protein Evolution.
Journal, issue, pagesMol Biol Evol, Vol. 42, Issue 12, Year 2025
Publish dateNov 28, 2025
AuthorsRita Severino / Jorge Cuéllar / Jorge Gutiérrez-Seijo / Moisés Maestro-López / Luis Sánchez-Pulido / César Santiago / Mercedes Moreno-Paz / José María Valpuesta / Víctor Parro /
PubMed AbstractChaperonins are essential protein-folding machines, classified into three structural and phylogenetic groups: Group I (bacterial GroEL), Group II (archaeal thermosome and eukaryotic CCT), and Group ...Chaperonins are essential protein-folding machines, classified into three structural and phylogenetic groups: Group I (bacterial GroEL), Group II (archaeal thermosome and eukaryotic CCT), and Group III (bacterial thermosome-like). Using ancestral sequence reconstruction (ASR) and protein resurrection, we inferred and experimentally characterized the last common ancestors of these groups (ancestral chaperonins ACI, ACII, and ACIII). The resurrected proteins exhibited ATPase activity (except ACII) and protected client proteins from heat-induced inactivation. Structural analyses by electron microscopy and Cryo-EM revealed that ACI forms single 7-mer rings, whereas ACII adopts a mixed population of single/double 8-mer rings, representing the first experimental observation of intermediate oligomeric states. ACII also features a unique cochaperonin-independent closure mechanism, distinct from modern Group I and II chaperonins. Together, these findings provide the experimental structural reconstruction of the most ancient and complex multimeric proteins so far, uncover novel intermediate states in chaperonin evolution, and offer a direct empirical framework for studying the emergence of multimeric complexity in early cellular life.
External linksMol Biol Evol / PubMed:41310978 / PubMed Central
MethodsEM (single particle)
Resolution3.21 - 8.21 Å
Structure data

54339

9rwp

EMDB-54339, PDB-9rwp:
Ancestral Group II Chaperonin (ACII) Double-Ring in Closed Conformation
Method: EM (single particle) / Resolution: 3.69 Å

54340

9rwq

EMDB-54340, PDB-9rwq:
Ancestral Group III Chaperonin (ACIII) Double-Ring in Open Conformation including the Equatorial and Intermediate Domains (residues 12-200 and 356-507)
Method: EM (single particle) / Resolution: 3.21 Å

54341

9rwr

EMDB-54341, PDB-9rwr:
Ancestral Fibrobacteres-Chlorobi-Bacteroidetes Group Chaperonin (AFCB) Double-Ring in Open Conformation
Method: EM (single particle) / Resolution: 3.45 Å

EMDB-54342: 3D Reconstruction of Ancestral Group I Chaperonin (ACI) Single-Ring
Method: EM (single particle) / Resolution: 5.38 Å

EMDB-54343: 3D Reconstruction of Ancestral Group II Chaperonin (ACII) Double-Ring in Open Conformation
Method: EM (single particle) / Resolution: 3.92 Å

EMDB-54344: 3D Reconstruction of Ancestral Group II Chaperonin (ACII) Single-Ring in Closed Conformation
Method: EM (single particle) / Resolution: 7.49 Å

EMDB-54345: 3D Reconstruction of Ancestral Group II Chaperonin (ACII) Single-Ring in Open Conformation
Method: EM (single particle) / Resolution: 8.21 Å

Chemicals

ChemComp-ADP:
ADENOSINE-5'-DIPHOSPHATE / ADP, energy-carrying molecule*YM

ChemComp-MG:
Unknown entry

Source
  • synthetic construct (others)
  • Escherichia coli BL21(DE3) (bacteria)
KeywordsCHAPERONE / Chaperonins / Ancestors / Evolution / Cryoelectron Microscopy

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