Metabolic control of BRISC–SHMT2 assembly regulates immune signalling

Serine hydroxymethyltransferase 2 (SHMT2) regulates one-carbon transfer reactions that are essential for amino acid and nucleotide metabolism, and uses pyridoxal-5′-phosphate (PLP) as a cofactor. Apo SHMT2 exists as a dimer with unknown functions, whereas PLP binding stabilizes the active tetrameric state. SHMT2 also promotes inflammatory cytokine signalling by interacting with the deubiquitylating BRCC36 isopeptidase complex (BRISC), although it is unclear whether this function relates to metabolism. Here we present the cryo-electron microscopy structure of the human BRISC–SHMT2 complex at a resolution of 3.8 Å. BRISC is a U-shaped dimer of four subunits, and SHMT2 sterically blocks the BRCC36 active site and inhibits deubiquitylase activity. Only the inactive SHMT2 dimer—and not the active PLP-bound tetramer—binds and inhibits BRISC. Mutations in BRISC that disrupt SHMT2 binding impair type I interferon signalling in response to inflammatory stimuli. Intracellular levels of PLP regulate the interaction between BRISC and SHMT2, as well as inflammatory cytokine responses. These data reveal a mechanism in which metabolites regulate deubiquitylase activity and inflammatory signalling

First-in-class Deubiquitylase Inhibitors Reveal New Enzyme Conformations

Cells maintain protein homeostasis by adding a small protein, ubiquitin, to regulate a variety of cellular processes, dictating protein activity, localisation or degradation. The addition of ubiquitin, known as ubiquitylation, is a reversible process making it a versatile post-translational modification aptly suited for cell signalling. Removal of ubiquitin is catalysed by deubiquitylating enzymes, commonly referred to as DUBs. BRCC36 isopeptidase complex (BRISC) is a multi-protein DUB complex which hydrolyses lysine-63-linked ubiquitin chains on Type I interferon receptors (IFNAR1/2), thus regulating interferon-dependent signalling. Therefore, BRISC-mediated inflammatory signalling amplification is a promising target for autoimmune disease drug development. We performed a high-throughput screen to identify small molecules which inhibit BRISC enzymatic activity. Employing an integrative structural biology approach (cryo-electron microscopy, native mass spectrometry, hydrogen-deuterium exchange mass spectrometry), complemented with biochemical assays, we have uncovered new enzyme conformations, revealing a remarkable mode of action for BRISC inhibitors. Exploring these key mechanisms will expand current knowledge of inflammatory signalling pathways and establish the use of DUB inhibitors as therapeutics to combat autoimmune disease and hyperactive cytokine signalling

Inhibitors of adenosine consuming parasites through polymer-assisted N-acylation of N6-substituted 5'-amino-5'-deoxyadenosines

A series of 30 adenosine derivatives with three different substituents at the N(6)-position were prepared in order to evaluate their potential to inhibit the pathogenic protozoa Plasmodium falciparum and Trypanosoma brucei in vitro. The rationale for synthesis of these structures was the high probability of interactions with multiple adenosine associated targets and the assumption that N(6)-substitutents should increase stability against adenosine deaminases and allow the molecules to diffuse across parasite membranes. Starting from inosine, the new compounds were prepared as single isomers using a polymer-assisted acylation protocol enabling the straightforward isolation of the target compounds in pure form. Three of the compounds displayed anti-plasmodial and one anti-trypanosomal activity in the single digit micromolar concentration rang