Biochemistry and Molecular Biology

University of Texas Medical Branch


Faculty

D. Wayne Bolen, Ph.D., Professor Emeritus

The research in my laboratory involves two closely related areas of protein physical chemistry: (1) the physico-chemical bases of the ability of naturally occurring protecting osmolytes to stabilize proteins, and (2) the thermodynamics of denaturant-induced transitions of proteins.

Protein Stabilization by Naturally Occurring Osmolytes

Protein Stabilization by OsmolytesMany plants, animals and microorganisms have adapted to environmental stresses that normally denature proteins, and a mechanism of adaptation that protects the cellular components against denaturation involves the intracellular concentration of small organic molecules know as osmolytes.Two defining characteristics of protecting osmolytes are that they stabilize proteins against denaturing stresses, and their presence in the cell does not alter protein functional activity. The basic premise of our work is that natural selection of protecting osmolytes is based upon selection for a particular molecular-level that confers generic stabilization to all proteins without altering their functional activity. The goal of this work is to uncover that molecular-level property (or small set of properties), and delineate the molecular-level events that lead to generic protein stabilization without altering protein function.

It is known that the protecting osmolytes are preferentially excluded from the immediate vicinity of the protein surface, and this exclusion implies a solvophobic interaction between groups on the protein surface and the protecting osmolyte species.Transfer Gibbs energy measurements evaluate the propensities of all amino acid side chains and the peptide backbone to interact with osmolytes.These measurements identify the unfavorable interaction of the peptide backbone with the protecting osmolyte as the source of the solvophobic interaction and we have named this the osmophobic effect. Because the peptide unit is the most numerous grouping in proteins and denaturation exposes considerable backbone, the Gibbs energy of the denatured state in the presence of a strong protecting osmolyte such as trimethylamine N-oxide (TMAO) is raised significantly compared to the Gibbs energy of the native state.his gives rise to osmolyte-induced stabilization of the protein.

By means of the osmophobic effect, the protecting osmolytes contribute an additional driving force to protein folding that ensures protein stabilization in the face of the denaturing environmental stress. The osmophobic effect adds a new dimension to the protein-folding problem.Our goals have now turned to the effects this new force has on the thermodynamics, kinetics, intermediates, and molecular associations in protein folding.

The Thermodynamics of Protein Folding

The denatured state of a protein is implicated in a number of disease states, and plays a functionally important role in such biologically important process as transport across membranes, protein degradation and protein folding.It is the long-term goal of this work to elucidate the thermodynamic properties of the denatured ensemble, and thereby understand how these properties relate to the compactness of the denatured state, and to the denaturation Gibbs energy changes used in assessing the stability of proteins.This project will focus on a class of proteins whose denatured ensembles continue to change their thermodynamic characters as a function of denaturant concentration.The "variable" thermodynamic behavior of the denatured ensembles of such proteins contrasts dramatically with the "fixed" behavior exhibited by proteins whose denatured ensembles do not change their thermodynamic properties as a function of denaturant. Our ultimate aim is to provide a strong foundation for thermodynamic measurements of protein stability, a foundation that at present is weak or invalid for many proteins.