Co-cultivation is a powerful approach to produce a robust functionally designed synthetic consortium as a live biotherapeutic product (LBP).

The success of fecal microbiota transplants (FMT) has provided the necessary proof-of-concept for microbiome therapeutics. Yet, feces-based therapies have many associated risks and uncertainties, and hence defined microbial consortia that modify the microbiome in a targeted manner have emerged as a promising safer alternative to FMT. The development of such live biotherapeutic products has important challenges, including the selection of appropriate strains and the controlled production of the consortia at scale. Here, we report on an ecology- and biotechnology-based approach to microbial consortium construction that overcomes these issues. We selected nine strains that form a consortium to emulate the central metabolic pathways of carbohydrate fermentation in the healthy human gut microbiota. Continuous co-culturing of the bacteria produces a stable and reproducible consortium whose growth and metabolic activity are distinct from an equivalent mix of individually cultured strains. Further, we showed that our function-based consortium is as effective as FMT in counteracting dysbiosis in a dextran sodium sulfate mouse model of acute colitis, while an equivalent mix of strains failed to match FMT. Finally, we showed robustness and general applicability of our approach by designing and producing additional stable consortia of controlled composition. We propose that combining a bottom-up functional design with continuous co-cultivation is a powerful strategy to produce robust functionally designed synthetic consortia for therapeutic use.

Engineering Af1521 improves ADP-ribose binding and identification of ADP-ribosylated proteins.

Protein ADP-ribosylation is a reversible post-translational modification that regulates important cellular functions. The identification of modified proteins has proven challenging and has mainly been achieved via enrichment methodologies. Random mutagenesis was used here to develop an engineered Af1521 ADP-ribose binding macro domain protein with 1000-fold increased affinity towards ADP-ribose. The crystal structure reveals that two point mutations K35E and Y145R form a salt bridge within the ADP-ribose binding domain. This forces the proximal ribose to rotate within the binding pocket and, as a consequence, improves engineered Af1521 ADPr-binding affinity. Its use in our proteomic ADP-ribosylome workflow increases the ADP-ribosylated protein identification rates and yields greater ADP-ribosylome coverage. Furthermore, generation of an engineered Af1521 Fc fusion protein confirms the improved detection of cellular ADP-ribosylation by immunoblot and immunofluorescence. Thus, this engineered isoform of Af1521 can also serve as a valuable tool for the analysis of cellular ADP-ribosylation under in vivo conditions.

Optimization of LTQ-Orbitrap Mass Spectrometer Parameters for the Identification of ADP-Ribosylation Sites.

ADP-ribosylation of proteins alters their function or provides a scaffold for the recruitment of other proteins, thereby regulating several important cellular processes. Mono- or poly-ADP-ribosylation is catalyzed by different ADP-ribosyltransferases (ARTs) that have different subcellular localizations and modify different amino acid acceptor sites. However, our knowledge of ADP-ribosylated proteins and their acceptor amino acids is still limited due to the lack of suitable mass spectrometry (MS) tools. Here, we describe an MS approach for the detection of ADP-ribosylated peptides and identification of the ADP-ribose acceptor sites, combining higher-energy collisional dissociation (HCD) and electron-transfer dissociation (ETD) on an LTQ-Orbitrap mass spectrometer. The presence of diagnostic ions of ADP-ribose in the HCD spectra allowed us to detect putative ADP-ribosylated peptides to target in a second LC-MS/MS analysis. The combination of HCD with ETD fragmentation gave a more comprehensive coverage of ADP-ribosylation sites than that with HCD alone. We successfully identified different ADP-ribose acceptor sites on several in vitro modified proteins. The combination of optimized HCD and ETD methods may be applied to complex samples, allowing comprehensive identification of ADP-ribosylation acceptor sites.

Identification of ADP-ribosylated peptides and ADP-ribose acceptor sites.

ADP-ribosylation is a post-translational modification of proteins that comprises the transfer of the ADP-ribose moiety from NAD+ to specific amino acid residues on substrate proteins or to ADP-ribose itself. It is catalyzed by ADP-ribosyltransferases, a family of currently 22 human proteins that all possess an ADP-ribosyltransferase catalytic domain. ADP-ribosylation is a reversible modification that can be hydrolyzed by ADP-ribosylhydrolases. In order to define the functional role of cellular ADP-ribosylation and the functional contribution of distinct ARTD family members, it is necessary to identify all ADP-ribosylated proteins, as well as their modified residues in the context of different cellular conditions and stresses. Here, we summarize the most recent progress in defining the cellular ADP-ribosylome and the efforts to detect ADP-ribose acceptor sites by enzymatic reactions and mass-spectrometry.

Proteome-wide identification of poly(ADP-Ribosyl)ation targets in different genotoxic stress responses.

Poly(ADP-ribos)ylation (PARylation) is a reversible posttranslational modification found in higher eukaryotes. However, little is known about PARylation acceptor proteins. Here, we describe a sensitive proteomics approach based on high-accuracy quantitative mass spectrometry for the identification of PARylated proteins induced under different cellular stress conditions. While confirming the majority of known PARylated substrates, our screen identifies numerous additional PARylation targets. In vivo and in vitro validation of acceptor proteins confirms that our methodology targets covalent PARylation. Nuclear proteins encompassing nucleic acid binding properties are prominently PARylated upon genotoxic stress, consistent with the nuclear localization of ARTD1/PARP1 and ARTD2/PARP2. Distinct differences in proteins becoming PARylated upon various genotoxic insults are observed, exemplified by the PARylation of RNA-processing factors THRAP3 and TAF15 under oxidative stress. High-content imaging reveals that PARylation affects the nuclear relocalization of THRAP3 and TAF15, demonstrating the potential of our approach to uncover hitherto unappreciated processes being controlled by specific genotoxic-stress-induced PARylation.

Macrodomain-containing proteins are new mono-ADP-ribosylhydrolases.

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 3ß (GSK3ß) 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.

Crosstalk between SET7/9-dependent methylation and ARTD1-mediated ADP-ribosylation of histone H1.4.

BACKGROUND: Different histone post-translational modifications (PTMs) fine-tune and integrate different cellular signaling pathways at the chromatin level. ADP-ribose modification of histones by cellular ADP-ribosyltransferases such as ARTD1 (PARP1) is one of the many elements of the histone code. All 5 histone proteins were described to be ADP-ribosylated in vitro and in vivo. However, the crosstalk between ADP-ribosylation and other modifications is little understood. RESULTS: In experiments with isolated histones, it was found that ADP-ribosylation of H3 by ARTD1 prevents H3 methylation by SET7/9. However, poly(ADP-ribosyl)ation (PARylation) of histone H3 surprisingly allowed subsequent methylation of H1 by SET7/9. Histone H1 was thus identified as a new target for SET7/9. The SET7/9 methylation sites in H1.4 were pinpointed to the last lysine residues of the six KAK motifs in the C-terminal domain (K121, K129, K159, K171, K177 and K192). Interestingly, H1 and the known SET7/9 target protein H3 competed with each other for SET7/9-dependent methylation. CONCLUSIONS: The results presented here identify H1.4 as a novel SET7/9 target protein, and document an intricate crosstalk between H3 and H1 methylation and PARylation, thus implying substrate competition as a regulatory mechanism. Thereby, these results underline the role of ADP-ribosylation as an element of the histone code.

Inheritance of silent rDNA chromatin is mediated by PARP1 via noncoding RNA.

Faithful propagation of specific chromatin states requires re-establishment of epigenetic marks after every cell division. How the original epigenetic signature is inherited after disruption during DNA replication is still poorly understood. Here, we show that the poly(ADP-ribose)-polymerase-1 (PARP1/ARTD1) is implicated in the maintenance of silent rDNA chromatin during cell division. We demonstrate that PARP1 associates with TIP5, a subunit of the NoRC complex, via the noncoding pRNA and binds to silent rRNA genes after their replication in mid-late S phase. PARP1 represses rRNA transcription and is implicated in the formation of silent rDNA chromatin. Silent rDNA chromatin is a specific substrate for ADP-ribosylation and the enzymatic activity of PARP1 is necessary to establish rDNA silencing. The data unravel a function of PARP1 and ADP-ribosylation that serves to allow for the inheritance of silent chromatin structures, shedding light on how epigenetic marks are transmitted during each cell cycle.

Identification of distinct amino acids as ADP-ribose acceptor sites by mass spectrometry.

ADP-ribosylation is a well-known post-translational protein modification, which regulates a variety of -cellular processes. The proteins able to catalyze mono- or poly ADP-ribosylation of proteins belong to the family of ADP-ribosyltransferases. A variety of nuclear proteins has been described to be ADP-ribosylated, including ARTD1 itself and histone proteins. Despite intensive research during the last 40 years, the acceptor amino acids in ARTD1 or histone proteins could be identified and confirmed only recently by MS/MS and by site-directed mutagenesis. The establishment of a standardized protocol including the specific enrichment of ADP-ribosylated proteins and peptides and subsequent mass spectrometric analysis allows the identification of ADP-ribose acceptor sites of modified proteins and to address the functional contribution of ADP-ribosylation in vitro as well as in vivo.