Worcester Lab - University of Missouri, Columbia

University of Missouri - Columbia Division of Biological Sciences

Worcester Lab

Our laboratory is interested in the structure-function relationships of biomolecules from both an experimental and a theoretical perspective .

Molecular structure and dynamics of membrane components are being studied in lipid model membranes, cylindrical and other aggregates of chlorophylls and cadherin proteins. The research uses scattering and computational techniques.

Chlorophylls form hollow cylindrical aggregates upon hydration in nonpolar solvents. Cylinder diameters depend on chlorophyll type. Many preparations have been studied by neutron scattering and absorption spectroscopy. Three discrete values for the diameters have been observed and are in the ratio 1:2:4. These values result from specific types of chlorophyll interactions and can be accounted for if specific pairs of chlorophyll molecules form the basic structural units in the two larger diameter cylinders. This indicates stability in pairs of chlorophyll molecules; pairs such as are present in the reaction centers of photosynthetic bacteria, for example.

Cylinders of chlorophyll are present in green photosynthetic bacteria. Rings of chlorophylls are present in the light harvesting complexes of purple photosynthetic bacteria. Such chlorophyll aggregates are usually accompanied by red-shifted absorption spectra. In plants, there is little red shift and similarly, we have found that mixed Chl-a/Chl-b aggregates have little red shift. Using computational quantum chemistry we are examining if the presence of Chl-b is responsible for inhibiting the formation of very red-shifted species which are disadvantageous to photosynthesis.

Using computational quantum chemistry with the Gaussian software package at MU and NCSA, we are examining ligand cooperativity effects in calcium binding by cadherins. Cadherin proteins bind three calcium ions in a close luster and two clusters are brought together in cadherin dimerization. Characterizing the energetics of the calcium binding computationally has demonstrated cooperativity and its nature, as well as charge transfer effects that are not accounted for in molecular dynamics simulations.

D.L. Worcester, and J.J. Katz. 1996. Cylindrical aggregates of Chlorophylls studied by small-angle neutron scattering. In: Neutrons in Biology, p.227-237. B. Schoenborn and R. Knott, editors. Plenum Publishing Corporation.

Worcester, D.L. and B. Hammouda. 1998. Interdigitated hydrocarbon chains in C20 and C22 phosphatidylcholines induced by hydrostatic pressure. Physica B, 241: 1175-1177.

J.L. Finney and D.L. Worcester, editors. 2000. Series on Neutron Techniques and Applications - Vol. 2. Chick C. Wilson (Rutherford Appleton Lab, UK), "Single Crystal Neutron Diffraction From Molecular Materials". World Scientific Publishing CO.


	University of Missouri - Columbia		Division of Biological Sciences