Single-molecule Observation of Protein Folding in Symmetric GroEL-(GroES)2 Complexes

• Published in: The Journal of biological chemistry Vol. 287; no. 49; pp. 41118 - 41125
• Main Authors: Takei, Yodai, Iizuka, Ryo, Ueno, Taro, Funatsu, Takashi
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 30.11.2012; American Society for Biochemistry and Molecular Biology
• Subjects: Adenosine Triphosphatases - chemistry; Biophysics - methods; Chaperone Chaperonin; Chaperonin 60 - metabolism; Chaperonins - chemistry; Escherichia coli - metabolism; Escherichia coli Proteins - chemistry; Escherichia coli Proteins - metabolism; Fluorescence; Green Fluorescent Proteins - chemistry; GroEL; Kinetics; Microscopy; Microscopy, Fluorescence - methods; Models, Statistical; Protein Binding; Protein Folding; Protein Structure and Folding; Single Molecule Biophysics; Fluorescence; Single Molecule Biophysics; Microscopy; Chaperone Chaperonin; GroEL; Protein Folding
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M112.398628

The chaperonin, GroEL, is an essential molecular chaperone that mediates protein folding together with its cofactor, GroES, in Escherichia coli. It is widely believed that the two rings of GroEL alternate between the folding active state coupled to GroES binding during the reaction cycle. In other words, an asymmetric GroEL-GroES complex (the bullet-shaped complex) is formed throughout the cycle, whereas a symmetric GroEL-(GroES)2 complex (the football-shaped complex) is not formed. We have recently shown that the football-shaped complex coexists with the bullet-shaped complex during the reaction cycle. However, how protein folding proceeds in the football-shaped complex remains poorly understood. Here, we used GFP as a substrate to visualize protein folding in the football-shaped complex by single-molecule fluorescence techniques. We directly showed that GFP folding occurs in both rings of the football-shaped complex. Remarkably, the folding was a sequential two-step reaction, and the kinetics were in excellent agreement with those in the bullet-shaped complex. These results demonstrate that the same reactions take place independently in both rings of the football-shaped complex to facilitate protein folding. Background: Protein folding mediated by a symmetric GroEL-(GroES)2 complex is poorly understood. Results: Single-molecule imaging revealed that GFP folding proceeded in both rings of the symmetric GroEL-(GroES)2 complex. Conclusion: The same reaction occurs independently in both rings of the symmetric GroEL-(GroES)2 complex. Significance: The study provides insight into the mechanism of protein folding mediated by the symmetric GroEL-(GroES)2 complex.