4i45

Publication Abstract from PubMed

Thioesterase activity is typically required for the release of products from polyketide synthase enzymes, but no such enzyme has been characterized in deep-sea bacteria associated with the production of polyunsaturated fatty acids (PUFAs). In this work we have expressed and purified the Orf6 thioesterase from Photobacterium profundum. Enzyme assays reveal that Orf6 has a higher specific activity towards long-chain fatty acyl-CoA substrates (palmitoyl-CoA and eicosapentaenoyl-CoA) than towards short-chain or aromatic acyl-CoA substrates. We determined a high resolution (1.05 angstrom) structure of Orf6 that revealed a hotdog hydrolase fold arranged as a dimer of dimers. The putative active site of this structure was occupied by additional electron density not accounted for by the protein sequence, consistent with the presence of an elongated compound. A second crystal structure (1.40 angstrom) was obtained from a crystal that was grown in the presence of Mg2+, which revealed the presence of a binding site for divalent cations at a crystal contact. The Mg2+-bound structure showed localized conformational changes (RMSD = 1.63 angstrom), and its active site was unoccupied, suggesting a mechanism to open the active site for substrate entry or product release. These findings reveal a new thioesterase enzyme with a preference for long-chain CoA substrates in deep-sea bacteria which are being developed for bioremediation and for the production of biofuels.

Structure, activity and substrate selectivity of the Orf6 thioesterase from Photobacterium profundum.,Rodriguez-Guilbe M, Oyola-Robles D, Schreiter ER, Baerga-Ortiz A J Biol Chem. 2013 Feb 21. PMID:23430744^[1]

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