DJ-1 and Familial Parkinson's Disease

David Slochower '07 and Geetha Kannan '07

Biomolecule Index

I. Introduction

Parkinson's disease is a neurological disorder characterized by a slow loss of dopanergic neurons in the substantia nigra, resulting in a difficulty in initiating willed movement and tremors caused in part by an imbalance of dopamine and acetylcholine levels in the brain (Wilson, et al, 2003). DJ-1 is a conserved protein involved in familial Parkinson's disease, cancer, and male fertility (Huai, et al, 2003). Although the location of DJ-1 has not yet been found in humans, mice express DJ-1 mRNA in neuronal and non-neuronal populations of the substantia nigra, the red nucleus, the caudate putamen, the globus pallidus, and the deep nuclei of the cerebellum—structures involved in the motor system (Shang, et al, 2004). It is possible that DJ-1 is located in the same places in the human brain.

Mutation of a specific Leucine in DJ-1 causes an autosomal recessive form of familial Parkinson’s disease (Huai, et al, 2003). At this time the precise mechanism by which mutant DJ-1 causes Parkinson’s disease is under controversy, although oxidative stress and the incapability of mutant DJ-1 to form a dimer have been implicated (Huai, et al, 2003).

II. General Structure

The two prominent crystallizations of DJ-1 at 1.60 and 1.95 Å propose different structures of the protein (however, it should be noted that Protein Data Bank files are identical).

A. 1.60 Angstroms

The 1.60 Å X-ray crystallized monomer contains eight a-helices and 11 b-strands that form a "helix-strand-helix sandwich" (Huai, et al, 2003). The b-strands parallel meat or vegetables in a sandwich, while the a-helices are the slices of bread on either side. The central core is formed by a seven stranded b-sheet with all parallel strands except for B10 which is anti-parallel . The core is flanked on one side by three a-helices and on the other by five a-helices . Additionally, each side of the molecule contains two two stranded b-sheets (Huai, et al, 2003).

B. 1.95 Angstroms

A 1.95 Å crystallization of DJ-1 suggests a slightly different general morphology of the protein. This DJ-1 monomer takes on a flavodoxin-like Rossmann-fold rather than a helix-strand- helix sandwich. In this model, b-strand 6 is anti-parallel to the rest of the core intead of b-strand 10. The most significant deviation is the addition of a-helix 9 (Honbou, et al, 2003).

III. Dimer Formation and Mutations

In vivo, the assumed biological conformation of DJ-1 is a dimer composed of chain A and chain B . DJ-1 dimer formation is regulated through hydrogen bonding between His 126 of one monomer and Pro 184 of another monomer and hydrophobic interactions between His 126 and Val 186 of the other monomer (Honbou, et al, 2003). The interaction with Val 186 forces His 126 into an unfavorable conformation that causes the imidazole ring to form a catalytic dyad that prevents substrate binding to the protein.

A. Binding Pocket

The binding pocket is the portion of a molecule whose structure gives it the function to bind to specific substrates. The DJ-1 dimer has two binding pockets formed by Glu 18, Lys 32, Arg 48, Asn 76, Cys 100, Thr 110 and His 126 from one subunit ,and Arg 28 and Leu 185 from the neighboring subunit (Huai, et al, 2003) .

B. Leucine 166P

1.60 Angstroms

The 1.60 Å crystallographic structure shows that Leucine 166P (L166P) of H7 is involved in dimer formation with H8 of another DJ-1 monomer, forming a hydrophobic core within the dimer. This Leucine is located in the penultimate C-terminal of a-helix 7 (Cookson, 2003).

1.95 Angstroms

The 1.95 Å crystallographic structure positions Leu 166 in the middle of a-helix 8, forming a hydrophobic interaction with Val 181, Lys 182, and Leu 187 of a-helix 9. A mutation of Leu 166p into a Pro has been shown to break the helix (causing a 20-30 degree angle kink), as the Proline destabilizes the hydrophobic boundary between the eight and ninth a-helix, ultimately compromising the structural integreity of the dimer leading to early onset Parkinson’s disease (Honbou, et al, 2003). This mutation causes accelerated protein degradation of DJ-1 by some unknown mechanism, resulting in a decrease of DJ-1 dimer stability (Gorner, et al, 2004).

C. Cysteine 106 and Cysteine 53

Cys 106 is the equivalent residue composing the active site of DJ-1 homologs, as indicated by "structural data" (Cookson, 2003). The Ramachandran plot shows that Cys 106 is the only residue found in an energetically unfavorable form, consistent with the PfpI superfamily.

Additionally, Cys 106 was found to be very sensitive to radiation-induced oxidation, even during data collection. (Wilson, et al, 2003). In unpublished observations, Honbou noted that mutating Cys 53 to Alanine stops DJ-1 from responding to oxidative stress, and later proposed that His 126, located in close proximity to Cys 106, is the catalytic residue, commenting that the residues around Cys 106 are also highly conserved. Wilson (contrary to Honbou) concludes by speculating the flexibility of Cys 106 is responsible for DJ-1’s ability to bind a large number of substrates, from RNA to other proteins.

IV. Structural Neighbors

DJ-1 has numerous orthologs that include the E. coli heat shock protein HSP31 and members of the PfpI protease family ThiJ and PH1704 (Huai, et al, 2003). The protease family consists of catalases and enzymes used in thiamine biosynthesis (Bandyopadhyay, et al, 2004). The presence of a catalyitic triad of Cys100-His101 and Glu 74 in the active site of PH1704 enables the protein to exhibit protease activity. This triad is not conserved in DJ-1, although the active site is similar in shape and size to that of the DJ-1 dimer. DJ-1 has Cys 106, His 126, and Glu 18 in the nucleophilic elbow, but not in the correct conformation for catalytic activity (Wilson, et al, 2003). This suggests that the enzymatic mechanism of DJ-1 is not the same as that exhibited by the PH1704 protease. Rather than having a Cys-His-Glu triad as a catalytic mechanism, it is likely DJ-1 uses a Cys-His diad (Huai, et al, 2003).

V. References

Bandyopadhyay, Sourav, Mark R. Cookson. 2004. Evolutionary and functional relationships within the DJ1 superfamily. BMC Evolutionary Biology 4 (6)

Cookson, Mark R. 2003. Crystallizing ideas about Parkinson's disease. PNAS 100 (16): 9111-9113.

Gorner, Karin, Eve Holtorf, Sabine Odoy, Brigitte Nuscher, Ayako Yamamoto, Jorg T. Regula, Klaus Beyer, Christina Haass, and Philipp J. Kahle. 2004. Differential Effects of Parkinson's Disease-associated Mutations on Stability and Foding of DJ-1. The Journal of Biological Chemistry 279 (8): 6943:6951.

Honbou, Kazuya, Nobuo N. Suzuki, Masataka Horiuchi, Takeshi Niki, Takahiro Taira, Hiroyoshi Ariga, and Fuyuhiko Inagaki. 2003. The Crystal Structure of DJ-1, a Protein Related to Male Fertility and Parkinson's Disease. Journal of Biological Chemistry 278 (33): 31380- 31384.

Huai, Qing, Yingjie Sun, Huanchen Want, Lih-Shen Chin, Lian Li, Howard Robinson, Hengming Ke. 2003. Crystal structure of DJ-1/RS and implication on familial Parkinson's disease. FEBS Letters 549: 171-175.

Shang, Huifang, Doris Lang, Burgunder Jean-Marc, Alain Kaelin-Lang. 2004. Neuroscience Letters 367 (3): 273-277.