Alexander Nevzorov, NC State Univ., "Structure Determination of Membrane Proteins by Solid-State NMR: Uniaxial Alignment, Spectroscopic Assignment, and Structure Calculations"
Friday, February 10, 2012
Oriented-sample NMR (OS NMR) has emerged as a powerful technique for structure determination of membrane proteins in their native lipid environment. In OS NMR, the structural information is directly contained in the angular-dependent NMR frequencies. Several issues of critical importance for OS NMR are addressed. The first one is line narrowing due to uniaxial ordering and rotational diffusion. We have derived closed-form expressions for the NMR linewidths of uniaxially diffusing proteins and performed lineshape simulations using the more general Stochastic Liouville Equation. It was found that the linewidths contain as much structural information as the OS NMR frequencies, and can be used as a complementary structural restraint. Second, we have developed a method for the spectroscopic assignment of OS NMR spectra using magnetization transfer under the mismatched Hartmann-Hahn conditions. This allows one to transfer magnetization between the dilute spins that are over 6 Angstroms apart. The method is exemplified by solid-state NMR spectra of a single crystal and assignment of OS NMR spectra of Pf1 coat protein in the phage form and reconstituted in magnetically aligned bicelles. Finally, an algorithm that extracts three-dimensional structure entirely from the dipolar couplings is presented. Effect of experimental uncertainty on the quality of the calculated structures is assessed.