Our aims are to obtain a detailed understanding in quantitative terms of the mechanisms by which protein structure and assembly are stabilized by specific and non-specific ligands, of the linkages which exist between the binding of ligands to proteins and related conformational changes and self-assembly reactions which impart to proteins their biological function. Two specific problems will be investigated. The first one is the mechanism by which solvent components stabilize protein conformation and self-assembly. Specifically, the preferential interactions of solvent components with folded and unfolded proteins will be examined, the molecular mechanisms of the stabilizing solvent exclusion will be scrutinized and the manner in which such solvent components affect enzyme activity will be probed. In the second problem, the manner in which guanine nucleotides and divalent cations control the self-assembly of tubulin into microtubules and other structures will be probed. This will be done by careful thermodynamic studies of the various assembly reactions and an examination of the conformational changes which accompany ligand binding and assembly. The distances between various ligand binding sites and their perturbation by linked reactions will be measured by energy transfer fluorescence and nmr techniques. The methods used will be those of physical biochemistry, including sedimentation velocity, spectrofluorimetry, high precision densimetry, light scattering, quantitative gel chromatography, circular dichroism, surface tension, nmr, differential spectrophotometry. The data will be analyzed in terms of rigorous thermodynamic, hydrodynamic, and structural theory, with a full application of the coupling of the Wyman linkage functions with multicomponent thermodynamics and polymer solution theory. Where necessary, proteins and ligands will be chemically modified with proper markers. It is hoped through these studies to arrive at a better understanding of the controls of assembly of biological organelles and of the mechanisms of their function.
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