Structural analysis of GroE chaperonin complexes using chemical cross-linking

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• Chaperonins, such as GroEL and GroES, are essential molecular machines involved in protein folding.
• Understanding the precise arrangement and dynamics of these large oligomeric complexes is crucial for elucidating their function.
• Previous studies relied on techniques like electron microscopy (EM) for structural insights.

Purpose of the Study:

• To demonstrate the utility of chemical cross-linking using glutaraldehyde (GA) for investigating the structure of large chaperonin complexes.
• To confirm the subunit stoichiometry and arrangement within GroEL-GroES oligomers.
• To examine the impact of regulatory factors (nucleotides, cations) on chaperonin structure and dynamics.

Main Methods:

• Chemical cross-linking using a bifunctional reagent, glutaraldehyde (GA).
• Analysis of cross-linked products using denaturing electrophoresis.
• Characterization and quantitation of chaperonin heterooligomeric complexes in solution.

Main Results:

• Cross-linking confirmed the known subunit stoichiometry and arrangement of GroEL and GroES within complexes.
• The method allowed detailed examination of how nucleotides and divalent cations affect the molecular structure of GroEL and GroEL-GroES complexes.
• GA cross-linking accurately characterized and quantified various chaperonin complexes under functional conditions (protein folding, ATP hydrolysis).
• Glutaraldehyde did not induce artifactual changes in complex assembly or disassembly.

Conclusions:

• Chemical cross-linking with GA is a robust method for studying the structure and dynamics of large oligomeric protein complexes like chaperonins.
• This technique provides complementary and essential data, especially when subsequent analyses involve equilibrium-displacing methods.
• Cross-linking is a valuable tool for understanding chaperonin function and regulation in solution.