W0395

Crystal Structure of Yeast Hypothetical Protein YNQ8 Shows Putative HHDD Isomerase Activity. S. Eswaramoorthy, D. Kumaran, B. Daniels, F.W. Studier & S. Swaminathan, Biology Dept., Brookhaven National Laboratory, Upton, NY 11973, USA.

Yeast hypothetical protein YNQ8 (SWISS-PROT P53889), member of a seventeen protein family, was chosen for structural studies since neither structural nor functional information was available for any protein in this family at the time of selection. The structure has been solved by the MAD method using seleno-methionine crystals. Three wavelength MAD data were collected in the beamline X12C of NSLS, BNL and the heavy atom sub-structure was solved using SnB. Crystals belong to the space group P2₁2₁2₁ with cell dimensions a = 57.70, b = 85.99, and c = 316.70 Å with six molecules per asymmetric unit. This protein exists as a dimer in the crystal and contains mainly β strands. Each monomer consists of two β sheets, one more twisted and curved than the other and is in the interface of the dimer. The structure shows that it belongs to Fumarylacetoacetate (FAA) hydrolase fold and is similar to a bifunctional decarboxylase/isomerase whose structure is known. However, it has higher sequence similarity to a prokaryotic 2-hydroxyhepta-2,4-diene-1,7-dioate isomerase (HHDD isomerase, SWISS-PROT Q8U234) for which no structural information is available. We speculate that P096 will have only isomerase activity (unlike the bifunctional enzyme) and HHDD isomerase will have a similar structure. A calcium ion is coordinated to the putative active site triad formed by two GLU and one ASP residues. The structural details and the functional identification will be discussed.