Domain orientation and dynamics in multidomain proteins from residual dipolar couplings

Area of Science:

• Structural Biology
• Biophysics
• Protein Dynamics

Background:

• Macromolecular structure determination in solution often relies on short-range Nuclear Overhauser Effect (NOE) and spin-spin coupling data.
• Accurately positioning weakly interacting domains in multidomain proteins remains challenging due to the limited range of traditional methods.
• Aligned proteins in liquid crystalline solvents offer opportunities for long-range structural information via anisotropic spin interactions like residual dipolar couplings.

Purpose of the Study:

• To explore the relative domain orientation and dynamics of a two-domain barley lectin fragment.
• To apply residual dipolar couplings (RDCs) for long-range structural insights in solution.
• To compare singular value decomposition (SVD) with simulated annealing for determining domain order tensors.

Main Methods:

• Measurement of residual (15)N-(1)H dipolar couplings in liquid crystalline media.
• Application of singular value decomposition (SVD) to determine order tensors for individual domains.
• Comparison of SVD with simulated annealing for structural analysis.

Main Results:

• The two domains of barley lectin exhibit an orientation different from the crystal structure of wheat germ agglutinin.
• Differences in order tensor values indicate distinct reorientational dynamics for each domain.
• The domains appear to reorient largely independently, suggesting a lack of static positioning.

Conclusions:

• Residual dipolar couplings provide valuable long-range structural information for multidomain proteins in solution.
• Barley lectin domains display dynamic flexibility and independent reorientation, deviating from a static model.
• Potential specific interactions between a barley lectin domain and lipid bicelle solvent were observed.