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Mechanical denaturation : forced unfolding of proteins Li, Yongnan

Abstract

Mechanical denaturation has emerged as a novel method to study chemical and physical properties of protein molecules. In this thesis, single-molecule force spectroscopy has been carried out using the atomic force microscope to investigate the mechanical design of proteins through denaturation via an applied mechanical force. In the first study, a small globular protein has been shown to exhibit pronounced anisotropic response to directional mechanical stress. One protein can be both mechanically strong and weak. It will be strong when direction of the force vector is aligned with particular structural elements of the protein, and it will be weak otherwise. Mechanical denaturation in the strong direction is accompanied by cooperative disruption of intramolecular interactions in the protein. Conversely, mechanical denaturation in the weak direction is accompanied by sequential disruption of those same interactions. In the second study, the mechanical properties of a cofactor dependent protein is characterized. It is shown that both the protein and cofactor are mechanically strong in the presence of the cofactor. Removal of the cofactor tremendously diminishes the mechanical strength of the protein. The mutually supportive roles of structure and function are demonstrated through mechanical denaturation experiments.

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