It is highly unlikely that the biological functions of proteins will ever be fully understood solely on the basis of their structures in the crystalline state. Modern developments in NMR spectroscopy, in combination with the powerful distance geometry algorithm, now provide a means for the determination of protein structures in solution. The long term objective of this project is to develop a general strategy for resonance assignments and solution structure determination for proteins of moderate size (molecular weight up to about 10,000 or higher). Complete three-dimensional solution structures will be determined for proteins belonging to two different structural classes: predominantly Beta-barrel (plastocyanin) and predominantly Alpha-helical (the anaphylatoxin human C3a). The project will address several fundamental issues of protein structure and dynamics and should contribute greatly to understanding of structure-function correlations in these particular cases. The first goal of the present project will be to obtain virtually complete resonance assignments for plastocyanin and C3a. This will be achieved using phase sensitive two-dimensional scalar correlated (COSY), dipolar correlated (NOESY) and multiple quantum techniques and sequential assignment procedures. Various NMR parameters provide considerable information on the structure and dynamics of the proteins in solution. Solvent accessibility and conformational flexibility will be assessed via amide proton exchange measurements. Distance geometry methods will be used to determine the global conformations of the proteins in solution. Plastocyanin is regarded in part as a 'test' protein and detailed comparison of the solution and crystal structures will be made. This study will answer questions about the 'resolution' achievable for NMR structures. There is much evidence that the crystal and solution structures of C3a differ. Determination of the conformation of C3a in solution under physiological conditions will provide a basis for understanding its important function in inflammatory reactions.
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