(A) Ribbon representation of the overall structure of YML079wp monomer. Helices, strands from sheets S1 and S2, and loops are colored blue, pink, orange, and beige, respectively. The extra-strands beta2 and beta3 are colored in green. Secondary structure element labels correspond to those superposed onto aligned sequences in Figure 2. The guanine base is represented in sticks. (B) Representation of the dimer structure. The same color code as in A is used. Residues important for dimerization as well as bound guanine bases are shown as sticks.

We determined the three-dimensional crystal structure of the protein YML079wp, encoded by a hypothetical open reading frame from Saccharomyces cerevisiae to a resolution of 1.75 A. The protein has no close homologs and its molecular and cellular functions are unknown. The structure of the protein is a jelly-roll fold consisting of ten beta-strands organized in two parallel packed beta-sheets. The protein has strong structural resemblance to the plant storage and ligand binding proteins (canavalin, glycinin, auxin binding protein) but also to some plant and bacterial enzymes (epimerase, germin). The protein forms homodimers in the crystal, confirming measurements of its molecular mass in solution. Two monomers have their beta-sheet packed together to form the dimer. The presence of a hydrophobic ligand in a well conserved pocket inside the barrel and local sequence similarity with bacterial epimerases may suggest a biochemical function for this protein.