Structure
The crystal structure of the hydroxylase component of naphthalene 1,2-dioxygenase from Pseudomonas has been determined. The protein is an (αβ)3 hexamer. The β-subunit belongs to the α+β class. It has no prosthetic groups and its role in catalysis is unknown. The α-subunit can be divided into two domains: a Rieske domain that contains the center and the catalytic domain that contains the active site mononuclear iron. The Rieske domain (residues 38-158) consists of four β-sheets. The overall fold is very similar to that of the soluble fragment of the Rieske protein from bovine heart mitochondrial cytochrome bc1 complex. In the center, Fe1 is coordinated by two cysteine residues (Cys-81 and Cys-101) while Fe2 is coordinated by Nδ atoms of two histidine residues (His-83 and His-104). The catalytic domain belongs to the α+β class and is dominated by a nine-stranded antiparallel β-sheet. The iron of the active site is located at the bottom of a narrow channel, approximately 15 Å from the protein surface. The mononuclear iron is coordinated by His-208, His-213, Asp-362 (bidentate) and a water molecule. The geometry can be described as a distorted octahedral with one ligand missing. The structure of the hexamer suggests cooperativity between adjacent α-subunits, where electrons from the center in one α-subunit (A) are transferred to the mononuclear iron in the adjacent α-subunit (B) through AspB-205, which is hydrogen-bonded to HisA-104 of the Rieske center and HisB-208 of the active site.
Read more about this topic: Aromatic-ring-hydroxylating Dioxygenases
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“There is no such thing as a language, not if a language is anything like what many philosophers and linguists have supposed. There is therefore no such thing to be learned, mastered, or born with. We must give up the idea of a clearly defined shared structure which language-users acquire and then apply to cases.”
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