SARS-CoV-2 hijacks a cell damage response, which induces transcription of a more efficient Spike S-acyltransferase.

SARS-CoV-2 infection requires Spike protein-mediated fusion between the viral and cellular membranes. The fusogenic activity of Spike depends on its post-translational lipid modification by host S-acyltransferases, predominantly ZDHHC20. Previous observations indicate that SARS-CoV-2 infection augments the S-acylation of Spike when compared to mere Spike transfection.

Dynamics of CLIMP-63 S-acylation control ER morphology.

The complex architecture of the endoplasmic reticulum (ER) comprises distinct dynamic features, many at the nanoscale, that enable the coexistence of the nuclear envelope, regions of dense sheets and a branched tubular network that spans the cytoplasm. A key player in the formation of ER sheets is cytoskeleton-linking membrane protein 63 (CLIMP-63). The mechanisms by which CLIMP-63 coordinates ER structure remain elusive.

S-acylation controls SARS-CoV-2 membrane lipid organization and enhances infectivity.

SARS-CoV-2 virions are surrounded by a lipid bilayer that contains membrane proteins such as spike, responsible for target-cell binding and virus fusion. We found that during SARS-CoV-2 infection, spike becomes lipid modified, through the sequential action of the S-acyltransferases ZDHHC20 and 9. Particularly striking is the rapid acylation of spike on 10 cytosolic cysteines within the ER and Golgi.

Ligand Binding to the Collagen VI Receptor Triggers a Talin-to-RhoA Switch that Regulates Receptor Endocytosis.

Capillary morphogenesis gene 2 (CMG2/ANTXR2) is a cell surface receptor for both collagen VI and anthrax toxin. Biallelic loss-of-function mutations in CMG2 lead to a severe condition, hyaline fibromatosis syndrome (HFS). We have here dissected a network of dynamic interactions between CMG2 and various actin interactors and regulators, describing a different behavior from other extracellular matrix receptors.

Identification and dynamics of the human ZDHHC16-ZDHHC6 palmitoylation cascade.

S-Palmitoylation is the only reversible post-translational lipid modification. Knowledge about the DHHC palmitoyltransferase family is still limited. Here we show that human ZDHHC6, which modifies key proteins of the endoplasmic reticulum, is controlled by an upstream palmitoyltransferase, ZDHHC16, revealing the first palmitoylation cascade.

CMG2/ANTXR2 regulates extracellular collagen VI which accumulates in hyaline fibromatosis syndrome.

Loss-of-function mutations in capillary morphogenesis gene 2 (CMG2/ANTXR2), a transmembrane surface protein, cause hyaline fibromatosis syndrome (HFS), a severe genetic disorder that is characterized by large subcutaneous nodules, gingival hypertrophy and severe painful joint contracture. Here we show that CMG2 is an important regulator of collagen VI homoeostasis. CMG2 loss of function promotes accumulation of collagen VI in patients, leading in particular to nodule formation.

Ubiquitin-dependent folding of the Wnt signaling coreceptor LRP6.

Many membrane proteins fold inefficiently and require the help of enzymes and chaperones. Here we reveal a novel folding assistance system that operates on membrane proteins from the cytosolic side of the endoplasmic reticulum (ER). We show that folding of the Wnt signaling coreceptor LRP6 is promoted by ubiquitination of a specific lysine, retaining it in the ER while avoiding degradation.

Palmitoylated calnexin is a key component of the ribosome-translocon complex.

A third of the human genome encodes N-glycosylated proteins. These are co-translationally translocated into the lumen/membrane of the endoplasmic reticulum (ER) where they fold and assemble before they are transported to their final destination. Here, we show that calnexin, a major ER chaperone involved in glycoprotein folding is palmitoylated and that this modification is mediated by the ER palmitoyltransferase DHHC6.

Anthrax toxin triggers the activation of src-like kinases to mediate its own uptake.

AB-type toxins, like other bacterial toxins, are notably opportunistic molecules. They rely on target cell receptors to reach the appropriate location within the target cell where translocation of their enzymatic subunits occurs. The anthrax toxin, however, times its own uptake, suggesting that toxin binding triggers specific signaling events.

Functional interactions between anthrax toxin receptors and the WNT signalling protein LRP6.

To exert its activity, anthrax toxin must be endocytosed and its enzymatic toxic subunits delivered to the cytoplasm. It has been proposed that, in addition to the anthrax toxin receptors (ATRs), lipoprotein-receptor-related protein 6 (LRP6), known for its role in Wnt signalling, is also required for toxin endocytosis. These findings have however been challenged.

Palmitoylation and ubiquitination regulate exit of the Wnt signaling protein LRP6 from the endoplasmic reticulum.

Canonical Wnt signaling is initiated by binding of Wnt proteins to members of the Frizzled family and subsequent complex formation with lipoprotein receptor-related proteins 5/6 (LRP5/6). Here, we show that LRP6 is palmitoylated on a juxtamembranous cysteine and that palmitoylation is required for exit from the endoplasmic reticulum (ER). We propose that palmitoylation serves to tilt the long, 23-residue transmembrane domain of LRP6 with respect to the plane of membrane to prevent a hydrophobic mismatch and subsequent recognition by the ER quality control.

Simple and efficient isolation of hematopoietic stem cells from H2K-zFP transgenic mice.

We have generated a transgenic mouse line that allows for simple and highly efficient enrichment for mouse hematopoietic stem cells (HSCs). The transgene expresses a green fluorescent protein variant (zFP) under the control of H2Kb promoter/enhancer element. Despite the broad zFP expression, transgenic HSCs express exceptionally high levels of zFP, allowing prospective isolation of a population highly enriched in HSCs by sorting the 0.

Engineering substrate specificity of O6-alkylguanine-DNA alkyltransferase for specific protein labeling in living cells.

Fusion proteins of human O(6)-alkylguanine-DNA alkyltransferase (AGT) can be specifically labeled with a wide variety of synthetic probes in mammalian cells; this makes them an attractive tool for studying protein function. However, to avoid undesired labeling of endogenous wild-type AGT (wtAGT), the specific labeling of AGT fusion proteins has been restricted to AGT-deficient mammalian cell lines. We present here the synthesis of an inhibitor of wtAGT and the generation of AGT mutants that are resistant to this inhibitor.

Initiation and limitation of Ly-49A NK cell receptor acquisition by T cell factor-1.

The establishment of clonally variable expression of MHC class I-specific receptors by NK cells is not well understood. The Ly-49A receptor is used by approximately 20% of NK cells, whereby most cells express either the maternal or paternal allele and few express simultaneously both alleles. We have previously shown that NK cells expressing Ly-49A were reduced or almost absent in mice harboring a single or no functional allele of the transcription factor T cell factor-1 (TCF-1), respectively.

A role for the src family kinase Fyn in NK cell activation and the formation of the repertoire of Ly49 receptors.

NK cell function is regulated by a dual receptor system, which integrates signals from triggering receptors and MHC class I-specific inhibitory receptors. We show here that the src family kinase Fyn is required for efficient, NK cell-mediated lysis of target cells, which lack both self-MHC class I molecules and ligands for NKG2D, an activating NK cell receptor. In contrast, NK cell inhibition by the MHC class I-specific receptor Ly49A was independent of Fyn, suggesting that Fyn is specifically required for NK cell activation via non-MHC receptor(s).