The lysosome is the final destination for degradation of endocytic cargo, plasma membrane constituents, and intracellular components sequestered by macroautophagy. Fusion of endosomes and autophagosomes with the lysosome depends on the GTPase Rab7 and the homotypic fusion and protein sorting (HOPS) complex, but adaptor proteins that link endocytic and autophagy pathways with lysosomes are poorly characterized. Herein, we show that Pleckstrin homology domain containing protein family member 1 (PLEKHM1) directly interacts with HOPS complex and contains a LC3-interacting region (LIR) that mediates its binding to autophagosomal membranes. Depletion of PLEKHM1 blocks lysosomal degradation of endocytic (EGFR) cargo and enhances presentation of MHC class I molecules. Moreover, genetic loss of PLEKHM1 impedes autophagy flux upon mTOR inhibition and PLEKHM1 regulates clearance of protein aggregates in an autophagy- and LIR-dependent manner. PLEKHM1 is thus a multivalent endocytic adaptor involved in the lysosome fusion events controlling selective and nonselective autophagy pathways.

Ruijs-Aalfs syndrome is a segmental progeroid syndrome resulting from mutations in the SPRTN gene. Cells derived from patients with SPRTN mutations elicit genomic instability and people afflicted with this syndrome developed hepatocellular carcinoma. Here we describe the molecular mechanism by which SPRTN contributes to genome stability and normal cellular homeostasis. We show that SPRTN is a DNA-dependent mammalian protease required for resolving cytotoxic DNA-protein crosslinks (DPCs)— a function that had only been attributed to the metalloprotease Wss1 in budding yeast. We provide genetic evidence that SPRTN and Wss1 function distinctly in vivo to resolve DPCs. Upon DNA and ubiquitin binding, SPRTN can elicit proteolytic activity; cleaving DPC substrates and itself. SPRTN null cells or cells derived from patients with Ruijs-Aalfs syndrome are impaired in the resolution of covalent DPCs in vivo. Collectively, SPRTN is a mammalian protease required for resolving DNA-protein crosslinks in vivo whose function is compromised in Ruijs-Aalfs syndrome patients.DOI: http://dx.doi.org/10.7554/eLife.21491.001

The complicated process of eukaryotic ribosome biogenesis involves about 200 assembly factors that transiently associate with the nascent pre-ribosome in a spatiotemporally ordered way. During the early steps of 60S subunit formation, several proteins, collectively called A3 cluster factors, participate in the removal of the internal transcribed spacer 1 (ITS1) from 27SA3 pre-rRNA. Among these factors is the conserved hetero-trimeric Nop7–Erb1–Ytm1 complex (or human Pes1–Bop1–Wdr12), which is removed from the evolving pre-60S particle by the AAA ATPase Rea1 to allow progression in the pathway. Here, we clarify how Ytm1 and Erb1 interact, which has implications for the release mechanism of both factors from the pre-ribosome. Biochemical studies show that Ytm1 and Erb1 bind each other via their ß-propeller domains. The crystal structure of the Erb1–Ytm1 heterodimer determined at 2.67Å resolution reveals an extended interaction surface between the propellers in a rarely observed binding mode. Structure-based mutations in the interface that impair the Erb1–Ytm1 interaction do not support growth, with specific defects in 60S subunit synthesis. Under these mutant conditions, it becomes clear that an intact Erb1–Ytm1 complex is required for 60S maturation and that loss of this stable interaction prevents ribosome production.

Two members of the B-cell associated 31 (BAP31) family are found in humans; BAP29 and BAP31. These are ubiquitously expressed receptors residing in the endoplasmic reticulum. BAP31 functions in sorting of membrane proteins and in caspase-8 mediated apoptosis, while BAP29 appears to mainly corroborate with BAP31 in sorting. The N-terminal half of these proteins is membrane-bound while the C-terminal half is cytoplasmic. The latter include the so called variant of death effector domain (vDED), which shares weak sequence homology with DED domains. Here we present two structures of BAP31 vDED determined from a single and a twinned crystal, grown at pH 8.0 and pH 4.2, respectively. These structures show that BAP31 vDED forms a dimeric parallel coiled coil with no structural similarity to DED domains. Solution studies support this conclusion and strongly suggest that an additional α-helical domain is present in the C-terminal cytoplasmic region, probably forming a second coiled coil. The thermal stability of BAP31 vDED is quite modest at neutral pH, suggesting that it may assemble in a dynamic fashion in vivo. Surprisingly, BAP29 vDED is partially unfolded at pH 7, while a coiled coil is formed at pH 4.2 in vitro. It is however likely that folding of the domain is triggered by other factors than low pH in vivo. We found no evidence for direct interaction of the cytoplasmic domains of BAP29 and BAP31.

Highlights d Wss1 promotes replication stress tolerance d Wss1 catalytic activity is essential for replication stress tolerance d Histone accumulation is toxic to Wss1 mutant cells during replication stress d Wss1 targets histones bound to single-stranded DNA during replication stress