Cross correlation rates between Curie spin and dipole-dipole relaxation in paramagnetic proteins:: The case of Cerium substituted Calbindin D9k

Cross correlation rates between Curie spin relaxation and H-N dipole-dipole coupling (Gamma(HM,HN)(CS,DD)) have been determined for a calcium binding protein, Calbindin D-9k, in which one of the two calcium ions is substituted with cerium(III). Gamma(HM,HN)(CS,DD) values depend on both the metal-to-proton distances and the M-H-N angles and can be used as an additional constraint in order to refine the solution structure of paramagnetic metalloproteins. For this purpose, we have implemented a new module (CCR-DYANA) in a version of the program DYANA (PARAMAGNETIC-DYANA), which can be used together with other paramagnetism-based constraints such as pseudocontact shifts, residual dipolar couplings and hyperfine based Karplus relationships. This integrated structure calculation protocol has the advantage that different paramagnetic-based constraints are treated by the same algorithm in a way that the efficiency of each class of constraints can be analyzed and compared.