Protocatechuate 3,4-dioxygenase structure

A representative sampling of non-heme iron proteins is presented in Fig. 3. Evident from this atlas is the diversity of structural folds exhibited by non-heme iron proteins it may be safely concluded that there is no unique structural motif associated with non-heme iron proteins in general, or even for specific types of non-heme iron centers. Protein folds may be generally classified into several categories (i.e., all a, parallel a/)3, or antiparallel /8) on the basis of the types and interactions of secondary structures (a helix and sheet) present (Richardson, 1981). Non-heme iron proteins are found in all three classes (all a myohemerythrin, ribonucleotide reductase, and photosynthetic reaction center parallel a/)8 iron superoxide dismutase, lactoferrin, and aconitase antiparallel )3 protocatechuate dioxygenase, rubredoxins, and ferredoxins). This structural diversity is another reflection of the wide variety of functional roles exhibited by non-heme iron centers. 

One last class of mononuclear non-haem iron enzyme that we have not yet considered, consists of the microbial superoxide dismutases with Fe(III) at their active site. The crystal structure of the E. coli enzyme shows a coordination geometry reminiscent of protocatechuate 3,4-dioxygenase, with four endogenous protein ligands, three His and one Asp residue, and one bound water molecule (Carlioz et ah, 1988). 

Figure 2 X-Ray structure of the site active of protocatechuate 3,4-dioxygenase from Pseudomonas aeruginosa...

K. Sugimoto, T. Senda, H. Aoshima, E. Masai, M. Fukuda, and Y. Mitsui. 1999. Crystal structure of an aromatic ring opening dioxygenase LigAB, a protocatechuate 4,5-dioxygenase, under aerobic conditions Structure FoldDes. 1 953-965. (PubMed)... 

A view of the active site of protocatechuate 3,4-dioxygenase based on the results of the x-ray crystal structure. The Fe center is approximately trigonal bipyramidal, with Tyr-147 and His-162 as axial ligands, and Tyr-108 and His-160 in the equatorial plane along with a solvent molecule (not shown) in the foreground. ... 

Subunit Structure of Enzyme, Determination of the N-terminal amino acid in metapyrocatechase revealed that it contains about 2 moles of serine per mole of the enzyme, indicating that the enzyme consists of at least two peptide chains. Ultracentrifugal and diffusion analyses of the enzyme suggested that it was dissociated in 0.03N NaOH into two to three subunits. Likewise, protocatechuate 3,4-dioxygenase (19.4 ) was dissociated into small subunits (5.0s) in 0.05N NaOH, and electron microscope observation of the enzyme suggested that it consists of eight subunits. 

Figure 6. Proposed structures of the active site of protocatechuate 3,4-dioxygenase.

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