Biology subjects

Javitt, G.

Publications and source records attributed to Javitt, G..

4 recordsLinked to original sources

bioRxiv2022

Assembly of von Willebrand Factor Tubules with in Vivo Helical Parameters Requires A1 Domain Insertion

The von Willebrand factor (VWF) glycoprotein is stored in tubular form in Weibel-Palade bodies (WPBs) prior to secretion from endothelial cells into the bloodstream. The organization of VWF in the tubules promotes formation of covalently linked VWF polymers and enables orderly secretion without polymer tangling. Recent studies have described the high-resolution structure of helical tubular cores formed in vitro by the D1D2 and D'D3 amino-terminal protein segments of VWF. Here we show that formation of tubules with the helical geometry observed for VWF in intracellular WPBs requires also the VWA1 (A1) domain. We reconstituted VWF tubules from segments containing the A1 domain and discovered it to be inserted between helical turns of the tubule, altering helical parameters and explaining the increased robustness of tubule formation when A1 is present. The conclusion from this observation is that the A1 domain has a direct role in VWF assembly, along with its known activity in hemostasis post-secretion. Key pointsO_LIA cryo-EM structure shows that the A1 domain is necessary for forming VWF helical tubules matching those in Weibel-Palade bodies. C_LIO_LIThe A1 domain has a role in intracellular VWF supramolecular assembly in addition to platelet binding following secretion and activation. C_LI

molecular biology↗

bioRxiv2022

The Colon Mucosal Sialylglycome Is Redox-Regulated by the Golgi Enzyme QSOX1

Mucus shields the intestinal epithelium from pathogens and provides a supportive environment for commensal bacteria. Mucus is composed of enormous, heavily glycosylated proteins called mucins, which become disulfide crosslinked in a multi-step biosynthetic pathway culminating in the Golgi apparatus and secretory granules of goblet cells. We observed that knockout mice lacking the Golgi-localized disulfide catalyst QSOX1 produced poorly protective colon mucus, were hypersensitive to induced colitis, and had an altered microbiome. The initial hypothesis arising from these observations was that QSOX1 catalyzes disulfide crosslinking of mucins. Contrary to this hypothesis, the disulfide-mediated polymerization of mucins and related glycoproteins proceeded normally without QSOX1. Instead, we found that QSOX1 forms regulatory disulfides in Golgi glycosyltransferases and thereby promotes effective sialylation of the colon glycome. Our findings reveal that enzymatic control of Golgi redox state impacts glycan elaboration in goblet cells, and that this pathway is crucial for maintaining mucosal function.

cell biology↗

bioRxiv2022

Intestinal Mucin Is a Chaperone of Multivalent Copper

Mucus protects the body by many mechanisms, but a role in managing toxic transition metals was not previously known. Here we report that secreted mucins, the major mucus glycoproteins coating the respiratory and intestinal epithelia, are specific copper-binding proteins. Most remarkably, the intestinal mucin, MUC2, has two juxtaposed copper binding sites, one that accommodates Cu2+ and the other Cu1+, which can be formed in situ by reduction with vitamin C. Copper is an essential trace metal because it is a cofactor for a variety of enzymes catalyzing electron transfer reactions, but copper damages macromolecules when unregulated. We observed that MUC2 protects against copper toxicity while permitting nutritional uptake into cells. These findings introduce mucins, produced in massive quantities to guard extensive mucosal surfaces, as extracellular copper chaperones and potentially important players in physiological copper homeostasis.

biochemistry↗

bioRxiv2020

Assembly Mechanism of Mucin and von Willebrand Factor Polymers

The respiratory and intestinal tracts are exposed to physical and biological hazards accompanying the intake of air and food. Likewise, the vasculature is threatened by inflammation and trauma. Mucin glycoproteins and the related von Willebrand factor (VWF) guard the vulnerable cell layers in these diverse systems. Colon mucins additionally house and feed the gut microbiome. Here we present an integrated structural analysis of multimerized intestinal mucin MUC2. Our findings reveal the shared mechanism by which complex macromolecules responsible for blood clotting, mucociliary clearance, and the intestinal mucosal barrier form protective polymers and hydrogels. Specifically, cryo-electron microscopy and crystal structures show how disulfide-rich bridges and pH-tunable interfaces control successive assembly steps in the endoplasmic reticulum and Golgi. Remarkably, a densely O-glycosylated mucin domain performs a specific organizational role in MUC2. The mucin assembly mechanism and its adaptation for hemostasis provide the foundation for rational manipulation of barrier function and coagulation.

molecular biology↗