ADP-ribosylation is an important post-translational protein modification (PTM) that regulates diverse biological processes. ADP-ribosyltransferase diphtheria toxin-like 10 (ARTD10, also known as PARP10) mono-ADP-ribosylates acidic side chains and is one of eighteen ADP-ribosyltransferases that catalyze mono- or poly-ADP-ribosylation of target proteins. Currently, no enzyme is known that reverses ARTD10-catalyzed mono-ADP-ribosylation. Here we report that ARTD10-modified targets are substrates for the macrodomain proteins MacroD1, MacroD2 and C6orf130 from Homo sapiens as well as for the macrodomain protein Af1521 from archaebacteria. Structural modeling and mutagenesis of MacroD1 and MacroD2 revealed a common core structure with Asp102 and His106 of MacroD2 implicated in the hydrolytic reaction. Notably, MacroD2 reversed the ARTD10-catalyzed, mono-ADP-ribose-mediated inhibition of glycogen synthase kinase 3β (GSK3β) in vitro and in cells, thus underlining the physiological and regulatory importance of mono-ADP-ribosylhydrolase activity. Our results establish macrodomain-containing proteins as mono-ADP-ribosylhydrolases and define a class of enzymes that renders mono-ADP-ribosylation a reversible modification.

ADP-ribosylation is a posttranslational modification that exists in monomeric and polymeric forms. Whereas the writers (e.g. ARTD1/PARP1) and erasers (e.g. PARG, ARH3) of poly-ADP-ribosylation (PARylation) are relatively well described, the enzymes involved in mono-ADP-ribosylation (MARylation) have been less well investigated. While erasers for the MARylation of glutamate/aspartate and arginine have been identified, the respective enzymes with specificity for serine were missing. Here we report that, in vitro, ARH3 specifically binds and demodifies proteins and peptides that are MARylated. Molecular modeling and site-directed mutagenesis of ARH3 revealed that numerous residues are critical for both the mono- and the poly-ADP-ribosylhydrolase activity of ARH3. Notably, a mass spectrometric approach showed that ARH3-deficient mouse embryonic fibroblasts are characterized by a specific increase in serine-ADP-ribosylation in vivo under untreated conditions as well as following hydrogen peroxide stress. Together, our results establish ARH3 as a serine mono-ADP-ribosylhydrolase and as an important regulator of the basal and stress-induced ADP-ribosylome.

The X-ray crystal structures of the catalytic domain of the EphA3 tyrosine kinase in complex with two type I inhibitors previously discovered in silico (compounds A and B) were used to design type I1/2 and II inhibitors. Chemical synthesis of about 25 derivatives culminated in the discovery of compounds 11d (type I1/2), 7b, and 7g (both of type II), which have low-nanomolar affinity for Eph kinases in vitro and a good selectivity profile on a panel of 453 human kinases (395 nonmutant). Surface plasmon resonance measurements show a very slow unbinding rate (1/115 min) for inhibitor 7m. Slow dissociation is consistent with a type II binding mode in which the hydrophobic moiety (trifluoromethyl-benzene) of the inhibitor is deeply buried in a cavity originating from the displacement of the Phe side chain of the so-called DFG motif as observed in the crystal structure of compound 7m. The inhibitor 11d displayed good in vivo efficacy in a human breast cancer xenograft.

Web-based user interfaces to scientific applications are important tools that allow researchers to utilize a broad range of software packages with just an Internet connection and a browser.1 One such interface, CHARMMing (CHARMM interface and graphics), facilitates access to the powerful and widely used molecular software package CHARMM. CHARMMing incorporates tasks such as molecular structure analysis, dynamics, multiscale modeling, and other techniques commonly used by computational life scientists. We have extended CHARMMing’s capabilities to include a fragment-based docking protocol that allows users to perform molecular docking and virtual screening calculations either directly via the CHARMMing Web server or on computing resources using the self-contained job scripts generated via the Web interface. The docking protocol was evaluated by performing a series of “re-dockings” with direct comparison to top commercial docking software. Results of this evaluation showed that CHARMMing’s docking implementation is comparable to many widely used software packages and validates the use of the new CHARMM generalized force field for docking and virtual screening.

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