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An expanded protein folding cage in the GroEL-gp31 complex
Daniel K Clare1, Patrick J Bakkes, Harm van Heerikhuizen
1School of Crystallography, Birkbeck College, University of London, Malet Street, London WC1E 7HX, UK.
Journal of Molecular Biology
|March 22, 2006
Summary
Bacteriophage T4 gp31 protein works with E. coli GroEL to fold viral proteins. Cryo-EM reveals an expanded GroEL-gp31 cage, accommodating large viral coat proteins like gp23.
Area of Science:
- Structural biology
- Molecular biology
- Biophysics
Background:
- Bacteriophage T4 utilizes a GroES homolog, gp31, to assist the Escherichia coli GroEL chaperonin.
- This complex facilitates the folding of the bacteriophage's major coat protein, gp23.
Purpose of the Study:
- To determine the three-dimensional structure of the E. coli GroEL-gp31 complex.
- To understand how this complex accommodates large substrates like gp23.
Main Methods:
- Cryo-electron microscopy (cryo-EM) and image processing were employed.
- Three-dimensional structures of GroEL complexed with gp31 in the presence of ATP and ADP were obtained.
Main Results:
- A high-resolution (8.2 Å) 3D map of the GroEL-gp31-ADP complex was generated.
- Fitting of crystal structures revealed an expanded folding cage compared to the GroEL-GroES complex.
- The enlarged cage is suitable for folding the large 56 kDa gp23 coat protein.
Conclusions:
- The GroEL-gp31 complex forms an expanded chaperonin cage.
- This structural adaptation allows for the efficient folding of large viral proteins, such as gp23.
- The findings provide insights into substrate specificity and the mechanism of chaperonin-assisted protein folding.