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Publication Abstract from PubMed

PaaI thioesterases are members of the TE13 thioesterase family which catalyse the hydrolysis of thioester bonds between coenzyme A and phenylacetyl-CoA. In this study we characterize the PaaI thioesterase from Streptococcus pneumoniae (SpPaaI), including structural analysis based on crystal diffraction data to 1.8 A resolution, to reveal two double hotdog domains arranged in a back-to-back configuration. Consistent with the crystallography data, both size exclusion chromatography and small angle X-ray scattering data support a tetrameric arrangement of thioesterase domains in solution. Assessment of SpPaaI activity against a range of acyl-CoA substrates showed activity for both phenylacetyl-CoA and medium-chain fatty-acyl CoA substrates. Mutagenesis of putative active site residues reveals Asn37, Asp52, and Thr68 are important for catalysis, and size exclusion chromatography analysis and X-ray crystallography confirm that these mutants retain the same tertiary and quaternary structures, establishing that the reduced activity is not a result of structural perturbations. Interestingly, the structure of SpPaaI in the presence of CoA provides a structural basis for the observed substrate specificity, accommodating a 10-carbon fatty acid chain, and a large conformational change of up to 38 A in the N-terminus, and a loop region involving Tyr38Tyr39. This is the first time PaaI thioesterases have displayed a dual specificity for medium-chain acyl-CoAs substrates and phenylacetyl-CoA substrates, and we provide a structural basis for this specificity, highlighting a novel induced fit mechanism that is likely to be conserved within members of this enzyme family.

Structural and Functional Characterization of the PaaI Thioesterase from Streptococcus pneumoniae Reveals a Dual Specificity for Phenylacetyl-CoA and Medium-Chain Fatty Acyl-CoAs and a Novel CoA Induced Fit Mechanism.,Khandokar YB, Srivastava P, Sarker S, Swarbrick CM, Aragao D, Cowieson N, Forwood JK J Biol Chem. 2015 Nov 4. pii: jbc.M115.677484. PMID:26538563^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.