Affiliation:
1. Department of Biochemistry, The University of Iowa, Iowa City, Iowa 52242
2. The Questor Centre, The Queen's University of Belfast, Belfast BT9 5AG, Northern Ireland
Abstract
ABSTRACT
Rieske nonheme iron oxygenases form a large class of aromatic ring-hydroxylating dioxygenases found in microorganisms. These enzymes enable microorganisms to tolerate and even exclusively utilize aromatic compounds for growth, making them good candidates for use in synthesis of chiral intermediates and bioremediation. Studies of the chemical stability and thermostability of these enzymes thus become important. We report here the structure of free and substrate (indole)-bound forms of naphthalene dioxygenase from
Rhodococcus
sp. strain NCIMB12038. The structure of the
Rhodococcus
enzyme reveals that, despite a ∼30% sequence identity between these naphthalene dioxygenases, their overall structures superpose very well with a root mean square deviation of less than 1.6 Å. The differences in the active site of the two enzymes are pronounced near the entrance; however, indole binds to the
Rhodococcus
enzyme in the same orientation as in the
Pseudomonas
enzyme. Circular dichroism spectroscopy experiments show that the
Rhodococcus
enzyme has higher thermostability than the naphthalene dioxygenase from
Pseudomonas
species. The
Pseudomonas
enzyme has an apparent melting temperature of 55°C while the
Rhodococcus
enzyme does not completely unfold even at 95°C. Both enzymes, however, show similar unfolding behavior in urea, and the
Rhodococcus
enzyme is only slightly more tolerant to unfolding by guanidine hydrochloride. Structure analysis suggests that the higher thermostability of the
Rhodococcus
enzyme may be attributed to a larger buried surface area and extra salt bridge networks between the α and β subunits in the
Rhodococcus
enzyme.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
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