The haloacid dehalogenase (HAD) superfamily is one of the largest known groups of enzymes and the majority of its members catalyze the hydrolysis of phosphoric acid monoesters into a phosphate ion and an alcohol. Despite the fact that sequence similarity between HAD phosphatases is generally very low, the members of the family possess some characteristic features, such as a Rossmann-like fold, HAD signature motifs or the requirement for Mg2+ ion as an obligatory cofactor. This study focuses on a new hypothetical HAD phosphatase from Thermococcus thioreducens. The protein crystallized in space group P21212, with unit-cell parameters a = 66.3, b = 117.0, c = 33.8 Å, and the crystals contained one molecule in the asymmetric unit. The protein structure was determined by X-ray crystallography and was refined to 1.75 Å resolution. The structure revealed a putative active site common to all HAD members. Computational docking into the crystal structure was used to propose substrates of the enzyme. The activity of this thermophilic enzyme towards several of the selected substrates was confirmed at temperatures of 37°C as well as 60°C.

Department of Biologial Sciences University of Alabama in Huntsville 301 Sparkman Drive Huntsville AL 35899 USA

Institute of Biochemistry University of Lübeck Ratzeburger Allee 160 D 23538 Lübeck Germany

Institute of Chemistry Faculty of Science University of South Bohemia Branisovska 1760 CZ 370 05 Ceske Budejovice Czech Republic

Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences Flemingovo namesti 2 CZ 166 10 Prague Czech Republic

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