Crystal structures of human DJ-1 and Escherichia coli Hsp31, which share an evolutionarily conserved domain

Human DJ-1 and Escherichia coli Hsp31 belong to ThiJ/PfpI family, whose members contain a conserved domain. DJ-1 is associated with autosomal recessive early onset parkinsonism and Hsp31 is a molecular chaperone. Structural comparisons between DJ-1, Hsp31, and an Archaea protease, a member of ThiJ/PfpI family, lead to the identification of the chaperone activity of DJ-1 and the proteolytic activity of Hsp31. Moreover, the comparisons provide insights into how the functional diversity is realized in proteins that share an evolutionarily conserved domain. On the basis of the chaperone activity the possible role of DJ-1 in the pathogenesis of Parkinson's disease is discussed.     

Crystal structure of human DJ-1, a protein associated with early onset Parkinson's disease

We report the crystal structure at 1.8-A resolution of human DJ-1, which has been linked to early onset Parkinson's disease. The monomer of DJ-1 contains the alpha/beta-fold that is conserved among members of the DJ-1/ThiJ/PfpI superfamily. However, the structure also contains an extra helix at the C terminus, which mediates a novel mode of dimerization for the DJ-1 proteins. A putative active site has been identified near the dimer interface, and the residues Cys-106, His-126, and Glu-18 may play important roles in the catalysis by this protein. Studies with the disease-causing L166P mutant suggest that the mutation has disrupted the C-terminal region and the dimerization of the protein. The DJ-1 proteins may function only as dimers. The Lys to Arg mutation at residue 130, the site of sumoylation of DJ-1, has minimal impact on the structure of the protein.     

Residues near the amino terminus of Rns are essential for positive autoregulation and DNA binding

Most members of the AraC/XylS family contain a conserved carboxy-terminal DNA binding domain and a less conserved amino-terminal domain involved in binding small-molecule effectors and dimerization. However, there is no evidence that Rns, a regulator of enterotoxigenic Escherichia coli virulence genes, responds to an effector ligand, and in this study we found that the amino-terminal domain of Rns does not form homodimers in vivo. Exposure of Rns to the chemical cross-linker glutaraldehyde revealed that the full-length protein is also a monomer in vitro. Nevertheless, deletion analysis of Rns demonstrated that the first 60 amino acids of the protein are essential for the activation and repression of Rns-regulated promoters in vivo. Amino-terminal truncation of Rns abolished DNA binding in vitro, and two randomly generated mutations, I14T and N16D, that independently abolished Rns autoregulation were isolated. Further analysis of these mutations revealed that they have disparate effects at other Rns-regulated promoters and suggest that they may be involved in an interaction with the carboxy-terminal domain of Rns. Thus, evolution may have preserved the amino terminus of Rns because it is essential for the regulator's activity even though it apparently lacks the two functions, dimerization and ligand binding, usually associated with the amino-terminal domains of AraC/XylS family members.     

Dissection of the dimerization modes in the DJ-1 superfamily

The DJ-1 superfamily (DJ-1/ThiJ/PfpI superfamily) is distributed across all three kingdoms of life. These proteins are involved in a highly diverse range of cellular functions, including chaperone and protease activity. DJ-1 proteins usually form dimers or hexamers in vivo and show at least four different binding orientations via distinct interface patches. Abnormal oligomerization of human DJ-1 is related to neurodegenerative disorders including Parkinson’s disease, suggesting important functional roles of quaternary structures. However, the quaternary structures of the DJ-1 superfamily have not been extensively studied. Here, we focus on the diverse oligomerization modes among the DJ-1 superfamily proteins and investigate the functional roles of quaternary structures both computationally and experimentally. The oligomerization modes are classified into 4 types (DJ-1, YhbO, Hsp, and YDR types) depending on the distinct interface patches (I-IV) upon dimerization. A unique, rotated interface via patch I is reported, which may potentially be related to higher order oligomerization. In general, the groups based on sequence similarity are consistent with the quaternary structural classes, but their biochemical functions cannot be directly inferred using sequence information alone. The observed phyletic pattern suggests the dynamic nature of quaternary structures in the course of evolution. The amino acid residues at the interfaces tend to show lower mutation rates than those of non-interfacial surfaces.     

Experimental and computational studies indicate the mutation of Glu12 to increase the thermostability of oligomeric protease from <Emphasis Type="Italic">Pyrococcus horikoshii</Emphasis>

The intracellular protease from Pyrococcus horikoshii (PhpI) is a member of the DJ-1/ThiJ/PfpI superfamily, which is suggested to be involved in cellular protection against environmental stresses. In this study, flexible docking approach was employed to dock the ligand into the active site of PhpI. By analyzing the results, active site architecture and certain key residues responsible for substrate specificity were identified on the enzyme. Our docking result indicates that Glu12 plays an important role in substrate binding. The kinetic experiment conducted by Zhan shows that the E12T mutant is more stable than that of the wild-type. We also predict that Glu15, Lys43, and Tyr46 may be important in the catalytic efficiency and thermostability of enzyme. The new structural and mechanistic insights obtained from computational study should be valuable for detailed structures and mechanisms of the member of the DJ-1 superfamily.