Abhishek, S. | bioRxiv Science

bioRxiv2019

UHRF1-SRA recognizes symmetric non-CG methylated DNA through dual-flip out of 5-methyl cytosines

Non-CG DNA methylation (non-mCG) is enriched in the genome of brain neurons and germline cells. Non-mCG is differentially distributed on neuronal X-chromosome in males and females. Accumulation of non-mCG during postnatal brain development correlates with reduced gene expression and inactivation of distal regulatory elements, and allele specific gene regulation. Recently, UHRF1 has been found to contribute to de novo non-CG methylation, however, whether UHRF1 could recognize non-mCG is not known. Here, we have demonstrated through calorimetric measurements that the SRA domain of UHRF1 can recognize mCH and fully-mCHG, types of non-mCG. Furthermore, our ITC binding analyses with methylated CG DNA (mCG) revealed 6-fold decrease in binding affinity for fully-mCG compared to hemi-mCG and, despite symmetrical 5mCs, stoichiometry of 1:1 for UHRF1 SRA binding to fully-mCG indicates UHRF1 may not form stable complex with fully-mCG DNA. In contrast, UHRF1 SRA recognizes fully-mCHG with a stoichiometry of 2:1 protein to DNA duplex, and has tighter binding compared to fully-mCG. Crystal structure of UHRF1 SRA bound to 5mC containing DNA in fully-mCHG context revealed dual flip-out mechanism of 5mC recognition. Altogether, this study indicates that UHRF1 SRA also recognizes non-mCG DNA, besides known hemi-mCG DNA and exhibits contrasting mechanisms for hemi-mCG and fully-mCHG DNA recognition. These findings may open a new window to investigate the biological function of non-CG methylation recognition by the UHRF1.

biophysics↗

bioRxiv2019

Computational insights into mechanism of AIM4-mediated inhibition of aggregation of TDP-43 protein implicated in ALS and evidence for in vitro inhibition of liquid-liquid phase separation (LLPS) of TDP-432C-A315T by AIM4.

TDP-43 is an RNA/DNA-binding protein of versatile physiological functions and it is also implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS) disease in addition to several other implicated proteins such as mutant SOD1 and FUS etc. Cytoplasmic mis-localization, liquid-liquid phase separation (LLPS) due to RNA depletion and aggregation of TDP-43 are suggested to be important TDP-43-toxicity causing mechanisms for the ALS manifestation. So far, therapeutic options for ALS are extremely minimal and ineffective therefore, multi-faceted approaches such as treating the oxidative stress and inhibiting the TDP-43s aggregation are being actively pursued. In our recent study, an acridine imidazolium derivative compound, AIM4, has been identified to have anti-TDP-43 aggregation propensity however, its mechanism of inhibition is not deciphered. In this study, we have utilized computational methods to examine binding site(s) of AIM4 in the TDP-43 structure and have also compared its binding efficiency with several other relevant compounds. We find that AIM4 has a binding site in the C-terminal amyloidogenic core region of amino acids aa: 288-319, which coincides with one of the key residue motifs that could potentially mediate liquid-liquid phase separation (LLPS) of TDP-43. Importantly, alike to the previously reported effects exerted by RNA molecules, we found that AIM4 could also inhibit the in vitro LLPS of a recombinantly purified C-terminal fragment TDP-432C bearing an A315T familial mutation. Antagonistic effects of AIM4 towards LLPS which is believed as the precursor process to the TDP-43s aggregation and the in silico prediction of a binding site of AIM4 on TDP-43 occurring in the same region, assert that AIM4 could be an important molecule for further investigations on TDP-43s anti-aggregation effects with relevance to the ALS pathogenesis.

bioinformatics↗