AUTHOR=Wu Qilong , Koliopoulos Marios G. , Rittinger Katrin , Stieglitz Benjamin TITLE=Structural basis for ubiquitylation by HOIL-1 JOURNAL=Frontiers in Molecular Biosciences VOLUME=Volume 9 - 2022 YEAR=2023 URL=https://www.frontiersin.org/journals/molecular-biosciences/articles/10.3389/fmolb.2022.1098144 DOI=10.3389/fmolb.2022.1098144 ISSN=2296-889X ABSTRACT=

The linear ubiquitin chain assembly complex synthesises linear Ub chains which constitute a binding and activation platform for components of the TNF signalling pathway. One of the components of LUBAC is the ubiquitin ligase HOIL-1 which has been shown to generate oxyester linkages on several proteins and on linear polysaccharides. We show that HOIL-1 activity requires linear tetra-Ub binding which enables HOIL-1 to mono-ubiquitylate linear Ub chains and polysaccharides. Furthermore, we describe the crystal structure of a C-terminal tandem domain construct of HOIL-1 comprising the IBR and RING2 domains. Interestingly, the structure reveals a unique bi-nuclear Zn-cluster which substitutes the second zinc finger of the canonical RING2 fold. We identify the C-terminal histidine of this bi-nuclear Zn-cluster as the catalytic base required for the ubiquitylation activity of HOIL-1. Our study suggests that the unique zinc-coordinating architecture of RING2 provides a binding platform for ubiquitylation targets.