engleski

Can Cross Correlated Curie Spin Relaxation in Paramagnetic Proteins Help in 3D Structure Determination?

Curie-spin relaxation (CSR), originating from the dipolar interaction between the nuclear and the thermally averaged electron magnetic moments, behaves like a single-spin interaction for the nuclear spins involved. Consequently, cross-correlation effects between CSR and dipole-dipole (DD) relaxation formally appear like interference effects between chemical shift anisotropy (CSA) and dipole-dipole relaxation. Cross-correlation effects between the H-N dipole-dipole interaction and the Curie spin relaxation of the HN protons through paramagnetic ions depend on the angle theta between the H-N bond and the vector connecting the proton with the paramagnetic centre. Due to the long-range effect of paramagnetic relaxation, such angle restraints could potentially provide a powerful tool for obtaining long-range structural information. In the figure below all H-N pairs for which cross correlation rates could be measured are highlighted in a schematic view of the low-spin CN-Mb and high spin F-Mb molecules. We have investigated by experiment and simulation the influence of the anisotropy of the magnetic susceptibility on DDxCSR relaxation effects for high- and low-spin met-myoglobin complexes and consequences on the angular constraints derived from these data. Using PCS (pseudo contact shift) data together with CSRxDD information turns out to be particularily well suited for such an approach. Practical application, however has to overcome some limitations which are imposed by he distance dependence and the usually unknown amount of CSAxDD cross correlation present, which bears the same relaxation signature as DDxCSR. Experimental and quantum chemical approaches to tackling these problems have been investigated. Potential and limitations of this approach will be discussed.

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