Figure 2.

“Nonclassical” and classical POMos and POTs. (A) “Nonclassical” {Mo₈} was found in the MoSto protein from A. vinelandii, and β-[Mo^VI₈O₂₆]^4– could be crystallized from a Na₂Mo^VIO₄ solution acidified to a pH lower than 5.^23c HisA156 and GluA126 are histidine and glutamate side chains. Color code: {MoO₆}, gray or purple; C, gray; N, blue; O, red. (B) “Nonclassical” [W^VI₃O₁₀H_xN₃]^(6–x)– {W₃} was found in the WSto protein from A. vinelandii; metatungstate [H₂W^VI₁₂O₄₀]^6– {W₁₂} with its {W₃} could be synthesized from a solution of Na₂W^VIO₄ acidified to pH ∼ 5.^23d HisA140, HisA′140, and HisA″140 are histidine side chains from three α subunits. Color code: {WO₆}, gray or purple; O, red. (C) Covalent binding of TEW²⁴ to the polyphenol oxidase cgAUS1.^25a The carboxylic O atoms of glutamic acid (Glu157) bind covalently to two W atoms of TEW, accompanied by a rearrangement within the Anderson–Evans structure resulting in a bent structure term.²⁴ For comparison, the normal Anderson–Evans structure is depicted as polyhedra in the inset to the left in a matching orientation. Color code: {WO₆}, gray or purple, where the gray color indicates “nonclassical” fragments in “classical” structures; {TeO₆}, pale yellow; C, gray; N, blue; O, red.