Fulvio Reggiori

Macroautophagy, hereafter referred to as autophagy, is a conserved, catabolic process that promotes cell survival by recycling unused or damaged cellular components and is enhanced in response to n...

Autophagy is a catabolic pathway characterized by the de novo formation of autophagosomes. Critical to this process are the autophagy-related (Atg) proteins Atg9, Atg2, and Atg18, which constitute ...

In contrast to the ubiquitin (Ub)-proteasome-system, which only degrades individual proteins, macroautophagy can eliminate protein complexes or aggregates, organelles and even pathogens. Terms such as mitophagy, aggrephagy, lysophagy and xenophagy have been coined based on the targeted substrate. In Ub-dependent selective macroautophagy, cargo selectivity is specified by E3 Ub ligases that append Ub chains that in turn are recognized by selective autophagy receptors (SARs), driving sequestration into autophagosomes. While several Ub-dependent SARs have been identified and characterized, the E3 Ub ligases that ultimately decide target fate remain poorly studied. In this review, we summarize what is known about the E3 Ub ligases involved in selective macroautophagy, with a particular emphasis on the degradation of mitochondria, protein aggregates, lysosomes and pathogens. A better characterization of these enzymes could improve therapeutic strategies for targeted degradation in acute and chronic diseases.

During macroautophagy, the de novo formation of the autophagosome at a membrane contact site (MCS) with the endoplasmic reticulum requires directional lipid flux for the growth of the initial phagophore before its sealing into an autophagosome and subsequent fusion with the lysosome/vacuole. It remains unclear, however, how the formation of this specialized MCS and the directionality of the lipid flux are controlled. Here, we present the structure of the key lipid transfer protein Atg2 from yeast solved together with its Atg18 binding partner, a phosphatidylinositol-3-phosphate (PtdIns3P) effector, using cryo-electron microscopy. We reveal a new interface in Atg2 that, together with PtdIns3P, is required for Atg18 recruitment and lipid transfer activity. Furthermore, we visualize lipid densities along the internal hydrophobic cavity of Atg2, providing structural evidence that Atg2 cavity is filled with lipids throughout the entire length, even when Atg2 is cytosolic. Finally, molecular dynamics simulations show that the complex generates membrane curvature, efficiently positioning the lipid channel of Atg2 towards the membrane to promote lipid transfer into the elongating phagophore.

The SARS-CoV-2 main protease (3CLpro) is a well-validated target for structure-guided inhibitor discovery. Here, we report α-aminomethyl tetrazole inhibitors accessed via the Ugi tetrazole multicomponent reaction (UT-4CR), enabling rapid exploration of non-classical chemical space. Initial design and modeling suggested a binding mode analogous to Ugi-derived (U-4CR) 3CLpro inhibitors, with heteroaromatic substituents engaging the S1 pocket. However, crystallographic analysis revealed an unexpected binding orientation in which the tetrazole core itself occupies the S1 pocket and forms the key interaction with His163, while the modeled substituents are solvent-exposed. This revised binding mode rationalizes the observed structure–activity relationships. Installation of an electrophilic warhead yielded covalent inhibitors with sub-micromolar enzymatic potency, and lead compound 2a displayed modest antiviral activity in infected cells. These results highlight UT-4CR-derived tetrazoles as a platform for probing the 3CLpro binding space and underscore the importance of early crystallographic validation.

The term autophagy defines intracellular transport systems for the delivery and degradation of intracellular components, including protein aggregates, organelles and pathogens, into endosomes, vacu...

The clinical outcome of SARS-CoV-2 infection spans from asymptomatic viral elimination to lethal COVID-19 pneumonia, which is due to type I interferon (IFN) deficiency in at least 15–20% of cases. We report two unrelated male patients with critical COVID-19 who are heterozygous for rare deleterious variants in RB1CC1, encoding the autophagy-related FIP200 protein. Airway epithelial cells genetically deprived of FIP200 or cell lines expressing the RB1CC1/FIP200 patient variants exhibit elevated SARS-CoV-2 replication and impaired autophagic flux. The antiviral function of FIP200 is independent of canonical autophagy and type I IFN, but involves the selective autophagy receptor NDP52. We identify a non-canonical function of FIP200 in a novel lysosomal degradation pathway, in which SARS-CoV-2 virions are targeted to single-membrane compartments for degradation of viral RNA in LC3B-positive acidified vesicles. This pathway is impaired in FIP200-deficient cells and in cells expressing FIP200 patient haplotypes. Collectively, we describe a cell-autonomous anti-SARS-CoV-2 restriction pathway, dependent on FIP200 and NDP52, and independent of canonical autophagy and type I IFN, which can underlie critical COVID-19 pneumonia.