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Conventional ubiquitination regulates key cellular processes by catalysing the ATP-dependent formation of an isopeptide bond between ubiquitin (Ub) and primary amines in substrate proteins 1 . Recently, the SidE family of bacterial effector proteins (SdeA, SdeB, SdeC and SidE) from pathogenic Legionella pneumophila were shown to use NAD+ to mediate phosphoribosyl-linked ubiquitination of serine residues in host proteins2, 3. However, the molecular architecture of the catalytic platform that enables this complex multistep process remains unknown. Here we describe the structure of the catalytic core of SdeA, comprising mono-ADP-ribosyltransferase (mART) and phosphodiesterase (PDE) domains, and shed light on the activity of two distinct catalytic sites for serine ubiquitination. The mART catalytic site is composed of an α-helical lobe (AHL) that, together with the mART core, creates a chamber for NAD+ binding and ADP-ribosylation of ubiquitin. The catalytic site in the PDE domain cleaves ADP-ribosylated ubiquitin to phosphoribosyl ubiquitin (PR-Ub) and mediates a two-step PR-Ub transfer reaction: first to a catalytic histidine 277 (forming a transient SdeA H277–PR-Ub intermediate) and subsequently to a serine residue in host proteins. Structural analysis revealed a substrate binding cleft in the PDE domain, juxtaposed with the catalytic site, that is essential for positioning serines for ubiquitination. Using degenerate substrate peptides and newly identified ubiquitination sites in RTN4B, we show that disordered polypeptides with hydrophobic residues surrounding the target serine residues are preferred substrates for SdeA ubiquitination. Infection studies with L. pneumophila expressing substrate-binding mutants of SdeA revealed that substrate ubiquitination, rather than modification of the cellular ubiquitin pool, determines the pathophysiological effect of SdeA during acute bacterial infection. Structural and functional investigations demonstrate how bacterial enzymes ubiquitinate host proteins.

Biomass is a possible renewable alternative to fossil carbon sources. Today, many bio-resources can be converted to direct substitutes or suitable alternatives to fossil-based fuels and chemicals. However, catalyst deactivation under the harsh, often liquid-phase reaction conditions required for biomass treatment is a major obstacle to developing processes that can compete with the petrochemical industry. This review presents recently developed strategies to limit reversible and irreversible catalyst deactivation such as metal sintering and leaching, metal poisoning and support collapse. Methods aiming to increase catalyst lifetime include passivation of low-stability atoms by overcoating, creation of microenvironments hostile to poisons, improvement of metal stability, or reduction of deactivation by process engineering.

Fe-ZSM-5 has been systematically investigated as catalyst for the selective catalytic reduction (SCR) of NO with NH3, concentrating on the active sites, the deactivation mechanism during hydrothermal aging and the chemical possibilities to stabilize this type of SCR catalyst. Regarding the active SCR sites, it could be shown that monomeric species start to become active at the lowest temperatures (Ea,app ? 36.3 ± 0.2 kJ/mol), followed by dimeric species at intermediate temperatures (Ea,app ? 77 ± 16 kJ/mol) and oligomeric species at high temperatures. Experiments with Fe-ZSM-5 samples, in which the Brønsted acidity was specifically removed, proved that Brønsted acidity is not required for high SCR activity and that NH3 can also be adsorbed on other acidic sites on the zeolite surface. The hydrothermal deactivation of Fe-ZSM-5 could be explained by the migration of active iron ions from the exchange sites. Parallel to the iron migration dealumination of the zeolite framework occurs, which has to be regarded as an independent process. The migration of iron can be reduced by the targeted reaction of the aluminum hydroxide groups in the lattice with trimethylaluminium followed by calcination. With respect to the application of iron zeolites in the SCR process in diesel vehicles, the most efficient stabilization method would be to switch from the ZSM-5 to the BEA structure type. The addition of NO2 to the feed gas is another effective measure to increase the activity of even strongly deactivated iron zeolites tremendously.

Modified nucleoside triphosphates (dNTPs) are a versatile platform for the generation of high-density functionalized nucleic acids. The enzymatic polymerization of dNTPs allows the introduction of sensible functionalities that might not be compatible with the standard automated synthesis of oligonucleotides. Their application to in vitro selections, an elegant chemical approach to Darwinian evolution, delivers modified aptamers and catalytic nucleic acids with potentially enhanced properties. This review article highlights some recent synthetic examples of dNTPs bearing functionalities that are either found in the active site of protein enzymes or have been employed in organocatalysis and further underscores their usefulness in the development of some modified catalytic nucleic acids with special emphasis on M2+-independent RNA-cleaving DNAzymes.