On Dec 20, 2010, at 1:16 PM, jlliu liu wrote: > it is also within hydrogen bonding distance to the main > chain N of another protein residue.
This also strongly suggests it is not Mg2+, which prefers hard ligands such as charged oxygen, rather than softer ligands like uncharged backbone nitrogens (the interactions are primarily electrostatic, rather than orbital-mediated).
