Human DJ-1, a disease-associated protein that protects cells from oxidative stress, contains an oxidation-sensitive cysteine (C106) that is essential for its cytoprotective activity. The origin of C106 reactivity is obscure, due in part to the absence of an experimentally determined pK a value for this residue. We have used atomic-resolution X-ray crystallography and UV spectroscopy to show that C106 has a depressed pK a of 5.4 ( 0.1 and that the C106 thiolate accepts a hydrogen bond from a protonated glutamic acid side chain (E18). X-ray crystal structures and cysteine pK a analysis of several site-directed substitutions at residue 18 demonstrate that the protonated carboxylic acid side chain of E18 is required for the maximal stabilization of the C106 thiolate. A nearby arginine residue (R48) participates in a guanidinium stacking interaction with R28 from the other monomer in the DJ-1 dimer and elevates the pK a of C106 by binding an anion that electrostatically suppresses thiol ionization. Our results show that the ionizable residues (E18, R48, and R28) surrounding C106 affect its pK a in a way that is contrary to expectations based on the typical ionization behavior of glutamic acid and arginine. Lastly, a search of the Protein Data Bank (PDB) produces several candidate hydrogen-bonded aspartic/glutamic acid-cysteine interactions, which we propose are particularly common in the DJ-1 superfamily.Cysteine thiolates are potent nucleophiles that are used by many proteins for catalysis, metal binding, or to facilitate post-translational modification. However, the solution pK a value of cysteine (8.3) is not within the optimal physiological pH range of most proteins. To render cysteine residues reactive, the thiol pK a must be depressed by stabilization of the conjugate thiolate anion by the protein environment. Multiple types of stabilizing interactions can decrease cysteine pK a values, including electrostatic complementarity with nearby cations (1, 2), the R-helix macropole (3), and hydrogen bonding to the thiol (4).The Parkinsonism-associated protein DJ-1 contains an oxidation-sensitive cysteine residue (C106 in human DJ-1) of unknown pK a that is required for the cytoprotective activity of the protein (5, 6). DJ-1 is a homodimeric protein of 189 amino acid monomers that is found both in the cytoplasm (7) and in the mitochondria (5, 8) and protects cells from various types of oxidative stress (5,(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). Although C106 has been shown to be essential for the protective function of DJ-1 in cell culture (5, 16) and Drosophila melanogaster (6), the specific biochemical activity of the protein that requires this cysteine residue is uncertain. Identifying the structural determinants of C106 ionization (and hence reactivity) is an essential first step in understanding how this conserved cysteine residue contributes to the neuroprotective activity of DJ-1.The reactive cysteine in human DJ-1 is one of the most highly conserved residues in the DJ-1 superfamily (19,20). Crystal s...

Background: Glyoxalases are a varied group of enzymes that detoxify methylglyoxal by converting it to D-lactate. Results: The Candida albicans glyoxalase Glx3 is important for yeast growth, especially in glycerol. Conclusion: Many yeasts contain a novel group of glyoxalases that are not redundant with previously characterized enzymes. Significance: This is the first demonstration of physiologically relevant glutathione-independent glyoxalases in fungi.

Page 7432. Due to a typographical error made in the final typesetting of this article, the third and fourths rows from the bottom of Table 1 should begin "rmsd for angle distances (Å)" and "rmsd for bond lengths (Å)", respectively.

Candida albicans is among the most common human fungal pathogens, causing a broad range of infections, including life-threatening systemic infections. The cell wall of C. albicans is the interface between the fungus and the innate immune system. The cell wall is composed of an outer layer enriched in mannosylated glycoproteins (mannan) and an inner layer enriched in ␤-(1,3)-glucan and chitin. Detection of C. albicans by Dectin-1, a C-type signaling lectin specific for ␤-(1,3)-glucan, is important for the innate immune system to recognize systemic fungal infections. Increased exposure of ␤-(1,3)-glucan to the immune system occurs when the mannan layer is altered or removed in a process called unmasking. Nanoscale changes to the cell wall during unmasking were explored in live cells with atomic force microscopy (AFM). Two mutants, the cho1Δ/Δ and kre5Δ/Δ mutants, were selected as representatives that exhibit modest and strong unmasking, respectively. Comparisons of the cho1Δ/Δ and kre5Δ/Δ mutants to the wild type reveal morphological changes in their cell walls that correlate with decreases in cell wall elasticity. In addition, AFM tips functionalized with Dectin-1 revealed that the forces of binding of Dectin-1 to all of the strains were similar, but the frequency of binding was highest for the kre5Δ/Δ mutant, decreased for the cho1Δ/Δ mutant, and rare for the wild type. These data show that nanoscale changes in surface topology are correlated with increased Dectin-1 adhesion and decreased cell wall elasticity. AFM, using tips functionalized with immunologically relevant molecules, can map epitopes of the cell wall and increase our understanding of pathogen recognition by the immune system.