Proteomic analysis of S-nitrosylated nuclear proteins in rat cortical neurons

The ability of neurons to modulate gene expression in response to extrinsic signals is necessary for proper brain function. S-nitrosylation is the covalent attachment of a nitric oxide (NO) moiety to cysteine thiols and is critical for transducing extracellular stimuli into specific patterns of gene expression. In the cerebral cortex, S-nitrosylation of histone deacetylase 2 (HDAC2) is required for gene transcription during neuronal development, however only few nuclear targets of Snitrosylation have been identified to date. Here, we used S-nitrosothiol Resin Assisted Capture (SNORAC) coupled with mass spectrometry analysis to identify 614 S-nitrosylated nuclear proteins. Of these, 131 proteins had never been shown to be S-nitrosylated in any system, and 612 are new targets of S-nitrosylation in neurons. The site(s) of S-nitrosylation were identified for 59% of the targets, and motifs containing single lysines found at 33% of these sites. In addition, lysine motifs were found to be necessary for promoting S-nitrosylation of HDAC2 and Methyl-CpG Binding Protein 3 (MBD3). Moreover, S-nitrosylation of the histone binding protein RBBP7 was found to be necessary for dendritogenesis. Overall, our study provides the first extensive characterization of Snitrosylated nuclear proteins in neurons and identifies putative S-nitrosylation motifs that may be shared with other targets of nitric oxide signaling

FAN1 controls mismatch repair complex assembly via MLH1 retention to stabilize CAG repeat expansion in Huntington's disease

CAG repeat expansion in the HTT gene drives Huntington’s disease (HD) pathogenesis and is modulated by DNA damage repair pathways. In this context, the interaction between FAN1, a DNA-structure-specific nuclease, and MLH1, member of the DNA mismatch repair pathway (MMR), is not defined. Here, we identify a highly conserved SPYF motif at the N terminus of FAN1 that binds to MLH1. Our data support a model where FAN1 has two distinct functions to stabilize CAG repeats. On one hand, it binds MLH1 to restrict its recruitment by MSH3, thus inhibiting the assembly of a functional MMR complex that would otherwise promote CAG repeat expansion. On the other hand, it promotes accurate repair via its nuclease activity. These data highlight a potential avenue for HD therapeutics in attenuating somatic expansion