This project combines theoretical modeling and laboratory measurements for determining the universal physical principles behind the organization and function of different macromolecular systems. The principal area of interes is interaction of proteins. The main focus of our experiments remains on forces responsible for self- assembly of collagen into fibers. During this past year we have completed a study of these forces in nonaqueous solvents. We have also continued measurements of the forces as well as kinetics and thermodynamics of fiber self-assembly in water, specifically addressing effects of transition metal ions, various mono- and polyhydric alcohols, sugars, and protein denaturant on the assembly of native and chemically modified collagen. These studies provide new evidence confirming our previous hypothesis about the role of surface water restructuring in collagen self-assembly and expanding our knowledge of the factors involved in the process. For example we have found that sugars and some polyols inhibit collagen self-assembly b competing with water and disrupting specific hydrogen-bonded water clusters that normally connect histidine-containing recognition sites. We have also discovered that surprisingly low (sub-physiological) concentrations of Zn2+ and Cu2+ have a drastic, direct effect on self-assembly. Apparently the ion bind with very high affinity to histidine in the recognition sites, disrupt normal recognition and cause mis-assembly by forming ion-histidine complexe crosslinking neighboring molecules into a wrong structure. While the importance of Zn2+ and Cu2+ in formation of connective tissue (presumed to be associated with Zn-dependent enzymes) is well-known in the medical literature, this direct effect on assembly of collagen fibers has never bee recognized and studied. The most significant theoretical development this year has been the analysi of structural and mechanical effects of diacylglycerol, a biological membrane second messenger, on highly curved phospholipid membranes. From experimental data on the energy of the reverse hexagonal phase as a functio of curvature and diacylglycerol content, we have deduced that diacylglycero affects the spontaneous curvature, but not the bending elasticity of lipid mixtures.
