The crystal structure of a hyper-thermophilic carboxylesterase from the archaeon Archaeoglobus fulgidus

The crystal structure of AFEST, a novel hyper-thermophilic carboxylesterase from the archaeon Archaeoglobus fulgidus, complexed with a sulphonyl deriv ative, has been determined and refined to 2.2 Angstrom resolution. This enz yme, which has recently been classified as a member of the hormone-sensitiv e-lipase (H) group of the esterase/lipase superfamily, presents a canonical alpha/beta hydrolase core, shielded on the C-terminal side by a cap region composed of five alpha -helices. It contains the catalytic triad Ser160, H is285 and Asp255, whereby the nucleophile is covalently modified and the ox yanion hole formed by Gly88, Gly89 and Ala16l. A structural comparison of A FEST with its mesophilic and thermophilic homologues, Brefeldin A esterase from Bacillus subtilis (BFAE) and EST2 from Alicyclobacillus acidocaldarius , reveals an increase in the number of intramolecular ion pairs and seconda ry structure content, as well as a significant reduction in loop extensions and ratio of hydrophobic to charged surface area. The variety of structura l differences suggests possible strategies for thermostabilization of lipas es and esterases with potential industrial applications. (C) 2001 Academic Press.