The YDR533c Structure(A) Ribbon representation of the YDR533c monomer. The core and the cap regions are in blue and pink, respectively. The nucleophile elbow is colored yellow. The residues constituting the putative catalytic triad (Cys138, His139, and Glu170) are shown as sticks.(B) Ribbon representation of the YDR533c homodimer. Colors are similar to (A). The two potential triads are at a distance of 31 Å. Some residues involved in dimer formation are shown as sticks.

The ORF YDR533c from Saccharomyces cerevisiae codes for a 25.5 kDa protein of unknown biochemical function. Transcriptome analysis of yeast has shown that this gene is activated in response to various stress conditions together with proteins belonging to the heat shock family. In order to clarify its biochemical function, we determined the crystal structure of YDR533c to 1.85 Å resolution by the single anomalous diffraction method. The protein possesses an small alpha, Greek/small beta, Greek hydrolase fold and a putative Cys-His-Glu catalytic triad common to a large enzyme family containing proteases, amidotransferases, lipases, and esterases. The protein has strong structural resemblance with the E. coli Hsp31 protein and the intracellular protease I from Pyrococcus horikoshii, which are considered class I and class III members of the Hsp31 family, respectively. Detailed structural analysis strongly suggests that the YDR533c protein crystal structure is the first one of a class II member of the Hsp31 family.