ADP-ribosylation is a reversible post-translational modification with wide-ranging biological functions in all kingdoms of life. A variety of enzymes use NAD(+) to transfer either single or multiple ADP-ribose (ADPr) moieties onto distinct amino acid substrates, often in response to DNA damage or other stresses. Poly-ADPr-glycohydrolase readily reverses poly-ADP-ribosylation induced by the DNA-damage sensor PARP1 and other enzymes, but it does not remove the most proximal ADPr linked to the target amino acid. Searches for enzymes capable of fully reversing cellular mono-ADP-ribosylation back to the unmodified state have proved elusive, which leaves a gap in the understanding of this modification. Here, we identify a family of macrodomain enzymes present in viruses, yeast and animals that reverse cellular ADP-ribosylation by acting on mono-ADP-ribosylated substrates. Our discoveries establish the complete reversibility of PARP-catalyzed cellular ADP-ribosylation as a regulatory modification.

Adenosine diphosphate (ADP)-ribosylation is a post-translational protein modification implicated in the regulation of a range of cellular processes. A family of proteins that catalyse ADP-ribosylation reactions are the poly(ADPribose) (PAR) polymerases (PARPs). PARPs covalently attach an ADP-ribose nucleotide to target proteins and some PARP family members can subsequently add additional ADP-ribose units to generate a PAR chain. The hydrolysis of PAR chains is catalysed by PAR glycohydrolase (PARG). PARG is unable to cleave the mono(ADP-ribose) unit directly linked to the protein and although the enzymatic activity that catalyses this reaction has been detected in mammalian cell extracts, the protein(s) responsible remain unknown. Here, we report the homozygous mutation of the c6orf130 gene in patients with severe neurodegeneration, and identify C6orf130 as a PARP-interacting protein that removes mono(ADP-ribosyl)ation on glutamate amino acid residues in PARP-modified proteins. X-ray structures and biochemical analysis of C6orf130 suggest a mechanism of catalytic reversal involving a transient C6orf130 lysyl-(ADP-ribose) intermediate. Furthermore, depletion of C6orf130 protein in cells leads to proliferation and DNA repair defects. Collectively, our data suggest that C6orf130 enzymatic activity has a role in the turnover and recycling of protein ADP-ribosylation, and we have implicated the importance of this protein in supporting normal cellular function in humans.

Poly-ADP-ribosylation is a post-translational modification catalyzed by PARP enzymes with roles in transcription and chromatin biology. Here we show that distinct macrodomains, including those of histone macroH2A1.1, are recruited to sites of PARP1 activation induced by laser-generated DNA damage. Chemical PARP1 inhibitors, PARP1 knockdown and mutation of ADP-ribose-binding residues in macroH2A1.1 abrogate macrodomain recruitment. Notably, histone macroH2A1.1 senses PARP1 activation, transiently compacts chromatin, reduces the recruitment of DNA damage factor Ku70-Ku80 and alters gamma-H2AX patterns, whereas the splice variant macroH2A1.2, which is deficient in poly-ADP-ribose binding, does not mediate chromatin rearrangements upon PARP1 activation. The structure of the macroH2A1.1 macrodomain in complex with ADP-ribose establishes a poly-ADP-ribose cap-binding function and reveals conformational changes in the macrodomain upon ligand binding. We thus identify macrodomains as modules that directly sense PARP activation in vivo and establish macroH2A histones as dynamic regulators of chromatin plasticity.

Posttranslational modifications play a key role in recruiting chromatin remodeling and modifying enzymes to specific regions of chromosomes to modulate chromatin structure. Alc1 (amplified in liver cancer 1), a member of the SNF2 ATPase superfamily with a carboxy-terminal macrodomain, is encoded by an oncogene implicated in the pathogenesis of hepatocellular carcinoma. Here we show that Alc1 interacts transiently with chromatin-associated proteins, including histones and the poly(ADP-ribose) polymerase Parp1. Alc1 ATPase and chromatin remodeling activities are strongly activated by Parp1 and its substrate NAD and require an intact macrodomain capable of binding poly(ADP-ribose). Alc1 is rapidly recruited to nucleosomes in vitro and to chromatin in cells when Parp1 catalyzes PAR synthesis. We propose that poly(ADPribosyl)ation of chromatin-associated Parp1 serves as a mechanism for targeting a SNF2 family remodeler to chromatin.Alc1 ͉ chromatin remodeling enzyme ͉ macrodomain ͉ poly-(ADP-ribose) polymerase ͉ Snf2-like ATPase I n eukaryotic cells, chromosomal DNA is packaged into nucleosomes, which are in turn folded into higher order nucleosome arrays in chromatin fibers. This packaging allows the Ϸ2 m of DNA that make up the human genome to fit into nuclei with diameters on the order of 2-6 m; however, it also blocks access to DNA of the machinery responsible for transcription, replication, and DNA repair. Eukaryotic organisms have evolved a set of chromatin modifying and remodeling enzymes that alter the structure of chromatin to control accessibility to the machineries responsible for DNA replication and repair and for transcription. These enzymes have been shown to be targeted to regions of modified chromatin by such domains as bromodomains, which can bind acetylated histones, or chromodomains, tudor domains, or MBT domains, which can interact with methylated histones (1-4).ALC1 (amplified in liver cancer 1), alternatively known as CHD1L, is a member of the SNF2 superfamily of ATPases, some of which function as chromatin remodeling enzymes (5-7). Sequence alignments suggest that Alc1 is similar to chromatin remodeling ATPases Snf2, Iswi, and Chd1, which have been implicated in transcription, DNA repair, and replication (7). Alc1 lacks identifiable chromo-, bromo-, tudor-, MBT, or other domains known to have chromatin targeting functions. Instead, it contains a carboxy-terminal macrodomain. Macrodomains have been shown through biochemical and structural analyses to bind ADP-ribose (8).Over 50% of human hepatocellular carcinoma (HCC) patients contain a chromosomal amplification at 1q21, which includes the ALC1 gene (9-11). Alc1-overexpressing cells exhibit increased colony formation in soft agar and increased tumorigenicity in nude mice (11), suggesting that ALC1 functions as an oncogene.While mounting evidence points to a potential role for Alc1 in oncogenesis, the molecular function of the Alc1 ATPase has not been studied. Here, we show that Alc1 is a chromatin remodeling enzyme that is recruited to nucleosom...

Drosophila cryptochrome (dCRY) is a FAD-dependent circadian photoreceptor, whereas mammalian cryptochromes (CRY1/2) are integral clock components that repress mCLOCK/mBMAL1-dependent transcription. We report crystal structures of full-length dCRY, a dCRY loop deletion construct, and the photolyase homology region of mouse CRY1 (mCRY1). Our dCRY structures depict Phe534 of the regulatory tail in the same location as the photolesion in DNA-repairing photolyases and reveal that the sulfur loop and tail residue Cys523 plays key roles in the dCRY photoreaction. Our mCRY1 structure visualizes previously characterized mutations, an NLS, and MAPK and AMPK phosphorylation sites. We show that the FAD and antenna chromophore-binding regions, a predicted coiled-coil helix, the C-terminal lid, and charged surfaces are involved in FAD-independent mPER2 and FBXL3 binding and mCLOCK/mBMAL1 transcriptional repression. The structure of a mammalian cryptochrome1 protein may catalyze the development of CRY chemical probes and the design of therapeutic metabolic modulators.