tailieunhanh - A Single-Molecule Perspective on the Role of Solvent Hydrogen Bonds in Protein Folding and Chemical Reactions

We present an array of force spectroscopy experiments that aim to identify the role of solvent hydrogen bonds in protein folding and chemical reactions at the single-molecule level. In our experiments we control the strength of hydrogen bonds in the solvent environment by substituting water (H2O) with deuterium oxide (D2O). Using a combination of force protocols, we demonstrate that protein unfolding, protein collapse, protein folding and a chemical reaction are affected in different ways by substituting H2O with D2O. We find that D2O molecules form an integral part of the unfolding transition structure of the immunoglobulin module of human cardiac titin, I27. Strikingly, we find that D2O is a worse solvent. | CHEMPHYSCHEM DOI A Single-Molecule Perspective on the Role of Solvent Hydrogen Bonds in Protein Folding and Chemical Reactions Lorna Dougan a Ainavarapu Sri Rama Koti b Georgi Genchev c Hui Lu c and Julio M. Fernandez a We present an array of force spectroscopy experiments that aim to identify the role of solvent hydrogen bonds in protein folding and chemical reactions at the single-molecule level. In our experiments we control the strength of hydrogen bonds in the solvent environment by substituting water H2O with deuterium oxide D2O . Using a combination of force protocols we demonstrate that protein unfolding protein collapse protein folding and a chemical reaction are affected in different ways by substituting H2O with D2O. We find that D2O molecules form an integral part of the unfolding transition structure of the immunoglobulin module of human cardiac titin I27. Strikingly we find that D2O is a worse solvent than H2O for the protein I27 in direct contrast with the behaviour of simple hydrocarbons. We measure the effect of substituting H2O with D2O on the force dependent rate of reduction of a disulphide bond engineered within a single protein. Altogether these experiments provide new information on the nature of the underlying interactions in protein folding and chemical reactions and demonstrate the power of single-molecule techniques to identify the changes induced by a small change in hydrogen bond strength. 1. Introduction The structure and dynamics of proteins and enzymatic activity is intrinsically linked to the strength and positions of hydrogen bonds in the system. 1 A hydrogen bond results from an attractive force between an electronegative atom and a hydrogen atom. 2 The hydrogen is attached to a strongly electronegative heteroatom such as oxygen or nitrogen termed the hydrogen-bond donor. This electronegative atom decentralizes the electron cloud around the hydrogen nucleus leaving the hydrogen atom with a positive partial .

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