Previous Article | Next Article ![]()
Journal of Bacteriology, July 2001, p. 4269-4277, Vol. 183, No. 14
Department of Biochemistry, Groningen
Biomolecular Sciences and Biotechnology Institute, University of
Groningen, 9747 AG Groningen, The Netherlands
Received 16 January 2001/Accepted 18 April 2001
The genes (caaD1 and caaD2)
encoding the trans-3-chloroacrylic acid
dehalogenase (CaaD) of the 1,3-dichloropropene-utilizing bacterium Pseudomonas pavonaceae 170 were cloned and
heterologously expressed in Escherichia coli and
Pseudomonas sp. strain GJ1. CaaD is a protein of 50 kDa
that is composed of
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.14.4269-4277.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
trans-3-Chloroacrylic Acid Dehalogenase from
Pseudomonas pavonaceae 170 Shares Structural and
Mechanistic Similarities with 4-Oxalocrotonate Tautomerase

-subunits of 75 amino acid residues and
-subunits of 70 residues. It catalyzes the hydrolytic cleavage of
the
-vinylic carbon-chlorine bond in
trans-3-chloroacrylic acid with a turnover number of 6.4 s
1. On the basis of sequence similarity, oligomeric
structure, and subunit size, CaaD appears to be related to
4-oxalocrotonate tautomerase (4-OT). This tautomerase consists of six
identical subunits of 62 amino acid residues and catalyzes the
isomerization of 2-oxo-4-hexene-1,6-dioate, via hydroxymuconate, to
yield 2-oxo-3-hexene-1,6-dioate. In view of the oligomeric architecture
of 4-OT, a trimer of homodimers, CaaD is postulated to be a hexameric
protein that functions as a trimer of 
-dimers. The sequence
conservation between CaaD and 4-OT and site-directed mutagenesis
experiments suggested that Pro-1 of the
-subunit and Arg-11 of the
-subunit are active-site residues in CaaD. Pro-1 could act as the
proton acceptor/donor, and Arg-11 is probably involved in carboxylate
binding. Based on these findings, a novel dehalogenation mechanism is
proposed for the CaaD-catalyzed reaction which does not involve the
formation of a covalent enzyme-substrate intermediate.
*
Corresponding author. Mailing address: Department of
Biochemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands. Phone: 31-50-3634209. Fax: 31-50-3634165. E-mail: d.b.janssen{at}chem.rug.nl.
Present address: Department of Microbiology, University of
Groningen, 9751 NN Haren, The Netherlands.
This article has been cited by other articles:
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»