Collaborative research between scientists at the Helmholtz Zentrum (Munich, Germany), Medical Research Council (Cambridge, UK), University of Oxford (Oxford, UK), UbiQ (Amsterdam, Netherlands) and the Walter and Eliza Hall Institute (Melbourne, Australia) is published in Nature Communications (2019, 10, article 4320) and outlines the identification of the DUB OTULIN as a regulator of the levels of nutrient transporters on the cell surface. This insight is important for potential treatments of metabolic diseases.

OTULIN (OTU Deubiquitinase With Linear Linkage Specificity) specifically hydrolyzes methionine1 (Met1)-linked ubiquitin chains conjugated by LUBAC (linear ubiquitin chain assembly complex). By mass spectrometric identification, the OTULIN interactor SNX27 (sorting nexin 27), was identified as an adaptor of the endosomal retromer complex responsible for protein recycling to the cell surface. The C-terminal PDZ-binding motif (PDZbm) in OTULIN associates with the cargo-binding site in the PDZ domain of SNX27. By solving the structure of the OTU domain in complex with the PDZ domain, we demonstrate that a second interface contributes to the selective, high affinity interaction of OTULIN and SNX27. SNX27 does not affect OTULIN catalytic activity, OTULIN-LUBAC binding or Met1-linked ubiquitin chain homeostasis. However, via association, OTULIN antagonizes SNX27-dependent cargo loading, binding of SNX27 to the VPS26A-retromer subunit and endosome-to-plasma membrane trafficking. In conclusion, we define an additional, non-catalytic function of OTULIN in the regulation of SNX27-retromer assembly and recycling to the cell surface.

To identify potential OTULIN interactors, UbiQ developed the biotin-labeled activity-based probe biotin-Ahx-Ub(1-75)-Dha-Ub (UbiQ-121), which couples with high selectivity to active OTULIN in cell extracts.

Figure 1. Left: structure of the OTULIN-SNX27 complex revealing the canonical PDZ-PDZbm interface. Structure of OTULIN (blue cartoon) bound to SNX27 (brown surface). The OTULIN catalytic center and also the OTULIN PDZbm are highlighted (dotted lines). Right: schematic model for the dual function of OTULIN. Through LUBAC binding and catalytic activity OTULIN controls Met1-ubiquitin chain homeostasis. By binding to SNX27 OTULIN counteracts cargo recruitment and retromer assembly to antagonize endosome-to-plasma membrane trafficking of internalized cargos. 

1. Institute of Molecular Toxicology and Pharmacology, Helmholtz Zentrum München, Neuherberg, Germany.
2. Medical Research Council Laboratory of Molecular Biology, Cambridge, UK.
3. Department of Biochemistry, University of Oxford, Oxford UK.
4. Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Oxford OX3 7FZ, UK.
5. Institute for Diabetes and Obesity, Helmholtz Zentrum München, German Centre for Diabetes Research (DZD), Neuherberg, Germany.
6. TUM School of Medicine, Technische Universität München, Munich, Germany.
7. UbiQ Bio BV, Amsterdam, The Netherlands.
8. Ubiquitin Signalling Division, The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia.
9. These authors contributed equally: Aurelia Stangl, Paul R. Elliott.