Structural basis for active single and double ring complexes in human mitochondrial Hsp60-Hsp10 chaperonin

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Mitochondrial chaperonins, like mHsp60-mHsp10, are crucial for protein folding within the mitochondrial matrix.
• Unlike bacterial GroEL-GroES, mHsp60-mHsp10 lacks negative ATP binding inter-ring cooperativity, suggesting a different mechanism for substrate processing.

Purpose of the Study:

• To elucidate the structural basis of mHsp60-mHsp10 function, particularly its ring formation and nucleotide dependence.
• To understand how single- and double-ring complexes contribute to the chaperonin reaction cycle.

Main Methods:

• Crystal structure determination of an ATP (ADP:BeF3-bound) mimic double-ring mHsp6014-(mHsp107)2 complex.
• Cryo-electron microscopy (cryo-EM) of ADP-bound double-ring and single-ring mHsp607-mHsp107 complexes.
• In vitro refolding assays and bacterial complementation analysis.

Main Results:

• Reported crystal and cryo-EM structures of mHsp60-mHsp10 complexes in different nucleotide-bound states, including double-ring and single-ring conformations.
• Structural analysis revealed the molecular basis for nucleotide-dependent ring formation and the absence of negative cooperativity.
• Demonstrated that both single- and double-ring mHsp60 variants are active in protein folding.

Conclusions:

• The study provides a structural framework for the coexistence of active single- and double-ring mHsp60-mHsp10 complexes.
• The findings explain the unique mechanism of mitochondrial chaperonins, distinct from bacterial counterparts.
• The research highlights the functional significance of both ring forms in the mHsp60-mHsp10 chaperonin system.