DJ-1 can form β-sheet structured aggregates that co-localize with pathological amyloid deposits

The loss of native function of the DJ-1 protein has been linked to the development of Parkinson's (PD) and other neurodegenerative diseases. Here we show that DJ-1 aggregates into β-sheet structured soluble and fibrillar aggregates in vitro under physiological conditions and that this process is promoted by the oxidation of its catalytic Cys106 residue. This aggregation resulted in the loss of its native biochemical glyoxalase function and in addition oxidized DJ-1 aggregates were observed to localize within Lewy bodies, neurofibrillary tangles and amyloid plaques in human PD and Alzheimer's (AD) patients' post-mortem brain tissue. These findings suggest that the aggregation of DJ-1 may be a critical player in the development of the pathology of PD and AD and demonstrate that loss of DJ-1 function can happen through DJ-1 aggregation. This could then contribute to AD and PD disease onset and progression.

Structural Basis of Small Molecule Targetability of Monomeric Tau Protein

The therapeutic targeting of intrinsically disordered proteins (IDPs) by small molecules has been a challenge due to their heterogeneous conformational ensembles. A potential therapeutic strategy to alleviate the aggregation of IDPs is to maintain them in their native monomeric state by small molecule binding. This study investigates the structural basis of small molecule druggability of native monomeric Tau whose aggregation is linked to the onset of Tauopathies such as Alzheimer's disease. Initially, two available monomeric conformational ensembles of a shorter Tau construct K18 (also termed Tau4RD) were analyzed which revealed striking structural differences between the two ensembles, while similar number of hot spots and small molecule binding sites were identified on monomeric Tau ensembles as on tertiary folded proteins of similar size. Remarkably, some critical fibril forming sequence regions of Tau (V306-K311, V275-K280) participated in hot spot formation with higher frequency compared to other regions. As an example of small molecule binding to monomeric Tau, it was shown that methylene blue (MB) bound to monomeric K18 and full-length Tau selectively with high affinity (K_d = 125.8 nM and 86.6 nM, respectively) with binding modes involving Cys291 and Cys322, previously reported to be oxidized in the presence of MB. Overall, our results provide structure-based evidence that Tau can be a viable drug target for small molecules and indicate that specific small molecules may be able to bind to monomeric Tau and influence the way in which the protein interacts among itself and with other proteins.

Structural features of human DJ-1 in distinct Cys106 oxidative states and their relevance to its loss of function in disease

DJ-1 (PARK7) is a multifunctional protein linked to the onset and progression of a number of diseases, most of which are associated with high oxidative stress. The Cys106 of DJ-1 is unusually reactive and thus sensitive to oxidation, and due to high oxidative stress it was observed to be in various oxidized states in disease condition. The oxidation state of Cys106 of DJ-1 is believed to determine the specific functions of the protein in normal and disease conditions. Here we report molecular dynamics simulation and biophysical experimental studies on DJ-1 in reduced (Cys106, S^-), oxidized (Cys106, SO₂^-), and over-oxidized (Cys106, SO₃^-) states. To simulate the different oxidation states of Cys106 in DJ-1, AMBER related force field parameters were developed and reported for 3-sulfinoalanine and cysteine sulfonic acid. Our studies found that the overall structure of DJ-1 in different oxidation states was similar globally, while it differed locally significantly, which have implications on its stability, function and its link to disease on-set. Importantly, the results suggest that over-oxidation may trigger loss of functions due to local structural modification in the Cys106 containing pocket of DJ-1 and structurally destabilize the dimeric state of DJ-1, which is believed to be its bioactive conformation. Such loss of functions would result in reduced ability of DJ-1 to protect from oxidative stress insults and may lead to increased progression of disease.