The three-dimensional structure of 4-hydroxybenzoyl-CoA thioesterase from Pseudomonas sp. strain CBS-3

The soil-dwelling microbe, Pseudomonas sp, strain CBS-3, has attracted rece nt attention due to its ability to survive on 4-chlorobenzoate as its sole carbon source. The biochemical pathway by which this organism converts 4-ch lorobenzoate to 4-hydroxybenzoate consists of three enzymes: 4-chlorobenzoy l-CoA ligase, 4-chlorobenzoyl-CoA dehalogenase, and 4-hydroxybenzoyl-CoA th ioesterase. Here we describe the three-dimensional structure of the thioest erase determined to 2.0-Angstrom resolution. Each subunit of the homotetram er is characterized by a five-stranded anti-parallel beta-sheet and three m ajor alpha-helices. While previous amino acid sequence analyses failed to r eveal any similarity between this thioesterase and other known proteins, th e results from this study clearly demonstrate that the molecular architectu re of 4-hydroxybenzoyl-CoA thioesterase is topologically equivalent to that observed for beta-hydroxydecanoyl thiol ester dehydrase from Escherichia c oli. On the basis of the structural similarity between these two enzymes, t he active site of the thioesterase has been identified and a catalytic mech anism proposed.