Small revisions to predicted distances around metal sites in proteins

Abstract

A new analysis has been made of distances around metal sites in protein structures in the Protein Data Bank determined with resolution < or =1.25 A and equivalent distances have been extracted from the Cambridge Structural Database. They are for the metals Na, Mg, K, Ca, Mn, Fe, Co, Cu, Zn and the donor atoms O of water, O of Asp and Glu, O of the main-chain carbonyl group, N of His and S of Cys. Some revisions are recommended to the tables of 'target distances' previously given. As well as small changes in many distances and a large improvement for Mg-O(carboxylate), the table includes an indication of how reliable each prediction may be. Special attention was given to carboxylate interactions. When the carboxylate group is monodentate, the M-O(carboxylate) distance is well defined, but for bidentate carboxylate groups a wide range of distances is allowable; when the metal is Co, Cu or Zn the M-O(1) and M-O(2) distances are clearly inversely correlated; for the more purely electrostatic interactions involving Na, K and Ca there is a wider scatter of distances and little correlation.