Neutron-encoded diubiquitins to profile linkage selectivity of deubiquitinating enzymes.

Deubiquitinating enzymes are key regulators in the ubiquitin system and an emerging class of drug targets. These proteases disassemble polyubiquitin chains and many deubiquitinases show selectivity for specific polyubiquitin linkages. However, most biochemical insights originate from studies of single diubiquitin linkages in isolation, whereas in cells all linkages coexist.

A MALDI-TOF Approach to Ubiquitin Ligase Activity.

In this issue of Cell Chemical Biology,De Cesare et al. (2018) report the development of a high-throughput assay that measures E2/E3 enzyme activity by MALDI-TOF mass spectrometry and apply this to screen for small molecule E3 inhibitors. This assay potentially accelerates the drug discovery for the ubiquitin ligation pathway.

Native chemical ligation at methionine bioisostere norleucine allows for N-terminal chemical protein ligation.

The development of γ-thionorleucine (ThioNle) as a handle for native chemical ligation-desulfurization is reported here. ThioNle is a new addition to the expanding thiolated amino acid toolbox and serves as a methionine substitute in NCL with the advantage that it lacks the undesirable oxidation-prone thioether moiety. Its usefulness for N-terminal ubiquitination is demonstrated by efficient preparation of fully synthetic linear diubiquitin with preserved protein folding compared to the expressed material.

Molecular basis of Lys11-polyubiquitin specificity in the deubiquitinase Cezanne.

The post-translational modification of proteins with polyubiquitin regulates virtually all aspects of cell biology. Eight distinct chain linkage types co-exist in polyubiquitin and are independently regulated in cells. This 'ubiquitin code' determines the fate of the modified protein.

Development of Diubiquitin-Based FRET Probes To Quantify Ubiquitin Linkage Specificity of Deubiquitinating Enzymes.

Deubiquitinating enzymes (DUBs) are proteases that fulfill crucial roles in the ubiquitin (Ub) system, by deconjugation of Ub from its targets and disassembly of polyUb chains. The specificity of a DUB towards one of the polyUb chain linkages largely determines the ultimate signaling function. We present a novel set of diubiquitin FRET probes, comprising all seven isopeptide linkages, for the absolute quantification of chain cleavage specificity of DUBs by means of Michaelis-Menten kinetics.