Reversible mechanical unfolding of single ubiquitin molecules.
Single-molecule manipulation techniques have enabled the characterization of the unfolding and refolding process of individual protein molecules, using mechanical forces to initiate the unfolding transition. Experimental and computational results following this approach have shed new light on the mechanisms of the mechanical functions of proteins involved in several cellular processes, as well as revealed new information on the protein folding/unfolding free-energy landscapes. To investigate how protein molecules of different folds respond to a stretching force, and to elucidate the effects of solution conditions on the mechanical stability of a protein, we synthesized polymers of the protein ubiquitin and characterized the force-induced unfolding and refolding of individual ubiquitin molecules using an atomic-force-microscope-based single-molecule manipulation technique. The ubiquitin molecule was highly resistant to a stretching force, and the mechanical unfolding process was reversible. A model calculation based on the hydrogen-bonding pattern in the native structure was performed to explain the origin of this high mechanical stability. Furthermore, pH effects were studied and it was found that the forces required to unfold the protein remained constant within a pH range around the neutral value, and forces decreased as the solution pH was lowered to more acidic values.
Chyan
Chia-Lin
CL
Department of Chemistry, National Dong Hwa University, Hualien, Taiwan.
Lin
Fan-Chi
FC
Peng
Haibo
H
Yuan
Jian-Min
JM
Chang
Chung-Hung
CH
Lin
Sheng-Hsien
SH
Yang
Guoliang
G
D003198:Computer Simulation; D004548:Elasticity; D019563:Mechanics; D008846:Micromanipulation / Q000379:methods*; D018625:Microscopy, Atomic Force / Q000379:methods*; D008956:Models, Chemical; D008958:Models, Molecular; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D013314:Stress, Mechanical; D013329:Structure-Activity Relationship; D025801:Ubiquitin / Q000737:chemistry* / Q000648:ultrastructure*
D025801:Ubiquitin