Crystallographic studies on B12 binding proteins in eukaryotes and prokaryotes

► Molecular architecture of the B12 binding proteins is diverse. ► Interaction of B12 with proteins in polar, non-polar and charged environments. ► B12 uses its functional groups at an optimum level for interactions with proteins. ► C-H···O hydrogen bonds play an important role in B12-protein interactions. ► B12 transport proteins in Escherichia coli shows adoptability of B12 between membrane and soluble proteins.