Generating accurate contact maps of transient long-range interactions in intrinsically disordered proteins by paramagnetic relaxation enhancement

摘要

The theory of paramagnetic relaxation for a rigid paramagnetic center was first set forth by Solomon (1) and Bloembergen (2) in the mid-1950s and early 1960s. The PRE is caused by magnetic dipolar interactions between a nucleus and the unpaired electron of a paramagnetic center and results in an increase in the relaxation rate of nuclear magnetization. Paramagnetic systems with an isotropic g-tensor only give rise to PRE effects, while systems with an anisotropic g tensor also result in pseudo-contact shifts. The observed PRE is proportional to the r~(-6) separation between the observed nucleus (e.g., a proton) and the paramagnetic center, and because the magnetic moment of an unpaired electron is large, the effects can extend to separations as long as ~35 A (e.g., in the case of Mn~(2+)). The most reliable approach for making use of the PRE is to measure the transverse PRE rate (GAMMA_2) which is obtained by taking the difference in transverse relaxation rates between the paramagnetic (e.g., Mn~(2+) or MTSL) and dia-magnetic (e.g., Ca~(2+) or MTS) states of the system (3,4).