51V NMR chemical shifts from quantum-mechanical/molecular-mechanical models of vanadium bromoperoxidase.

According to quantum-mechanical/molecular-mechanical (QM/MM) optimizations, the active-site geometries of vanadium-dependent bromoperoxidase (VBPO) and vanadium-dependent chloroperoxidase (VCPO) are very similar. 51V NMR chemical shifts calculated from QM/MM-optimized models of VBPO are critically compared to VCPO and are found to be very similar for the two related proteins. The primary difference between these related structures, the presence of a His411 in VBPO whereas Phe397 is located at that position in VCPO, is studied via analysis of the respective theoretical 51V NMR spectra. The long-range electrostatic effects from more distal residues are also studied to establish their effect. Similar results are obtained for the two active sites of the VBPO homodimer. The experimentally observed shielding of the isotropic 51V NMR chemical shift on going from VCPO to VBPO is somewhat underestimated in the QM/MM models studied. NMR and NQC tensors of both enzymes are predicted to show noticeable differences, suggesting that precise solid-state 51V NMR data, when they become available, can be a sensitive probe for subtle differences in structural details between these enzymes.