The human GID complex engages two independent modules for substrate recruitment

Abstract

The human GID (hGID) complex is an evolutionary conserved E3 ubiquitin ligase regulating diverse biological processes including glucose metabolism and cell cycle progression. However, the biochemical function and substrate recognition of the multi-subunit complex remains poorly understood. While the yeast GID complex recognizes Pro/N-end rule substrates via yeast Gid4, the human GID complex requires a WDR26/Gid7-dependent module to trigger proteasomal degradation of mammalian HBP1. Here, using biochemical assays, crosslinking-mass spectrometry and cryo-electron microscopy, we show that hGID unexpectedly engages two distinct modules for substrate recruitment, dependent on either WDR26 or GID4. WDR26 together with RanBP9 cooperate to ubiquitinate HBP1 in vitro, while GID4 is dispensable for this reaction. In contrast, GID4 functions as an adaptor for the substrate ZMYND19, which surprisingly lacks a Pro/N-end rule degron.