Pseudocontact shifts (PCS) are induced by paramagnetic centres which can be site specifically attached to proteins through metal binding tags. PCS are long range in nature (up to 40 Å from the metal centre), accurately measured with high sensitivity by chemical shift measurements using 2D NMR experiments and yield versatile structural information. Previously we have shown that PCS alone can be used as structural restraints in calculating 3D structures of proteins that up to 120 amino acids.
Here we describe a new method (GPS-Rosetta) to determine 3D structures of proteins ranging from 150-190 amino acids in size by simultaneously optimising Δχ tensors from multiple metal centres during structure calculation. Analogous to determining precise location on the earth by global positioning satellites, our method allows to determine the co-ordinates of nuclear spins in 3D space. The new algorithm is incorporated into the Rosetta ab initio protein structure determination software package which utilises protein backbone chemical shifts in generating fragments. To demonstrate, I'll present results from a statistically meaningful number of structure determinations using our new GPS-Rosetta protocol.
1. Schmitz, C., Vernon, R., Otting, G., Baker, D., and Huber, T. (2012). Protein structure determination from pseudocontact shifts using ROSETTA. J. Mol. Biol. 416, 668–677.