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J Bacteriol. 2000 Mar;182(6):1641-9.

Substrate specificity of naphthalene dioxygenase: effect of specific amino acids at the active site of the enzyme.

Author information

  • 1Department of Microbiology and Center for Biocatalysis and Bioprocessing, The University of Iowa, Iowa City, Iowa 52242, USA. rebecca-parales@uiowa.edu

Abstract

The three-component naphthalene dioxygenase (NDO) enzyme system carries out the first step in the aerobic degradation of naphthalene by Pseudomonas sp. strain NCIB 9816-4. The three-dimensional structure of NDO revealed that several of the amino acids at the active site of the oxygenase are hydrophobic, which is consistent with the enzyme's preference for aromatic hydrocarbon substrates. Although NDO catalyzes cis-dihydroxylation of a wide range of substrates, it is highly regio- and enantioselective. Site-directed mutagenesis was used to determine the contributions of several active-site residues to these aspects of catalysis. Amino acid substitutions at Asn-201, Phe-202, Val-260, Trp-316, Thr-351, Trp-358, and Met-366 had little or no effect on product formation with naphthalene or biphenyl as substrates and had slight but significant effects on product formation from phenanthrene. Amino acid substitutions at Phe-352 resulted in the formation of cis-naphthalene dihydrodiol with altered stereochemistry [92 to 96% (+)-1R,2S], compared to the enantiomerically pure [>99% (+)-1R,2S] product formed by the wild-type enzyme. Substitutions at position 352 changed the site of oxidation of biphenyl and phenanthrene. Substitution of alanine for Asp-362, a ligand to the active-site iron, resulted in a completely inactive enzyme.

PMID:
10692370
[PubMed - indexed for MEDLINE]
PMCID:
PMC94462
Free PMC Article

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