Biology subjects

Raote, I.

Publications and source records attributed to Raote, I..

8 recordsLinked to original sources

bioRxiv2025

Comparative ubiquitinomics of human skin reveals insulin receptor ubiquitination as a regulator of collagen secretion.

Ubiquitination is central to skin homeostasis and disease, however the cutaneous ubiquitinome remains poorly characterised. We investigated spatial patterns of ubiquitination in human skin, discovering specific ubiquitin linkages located within the hair follicle and epidermis. To create a comprehensive physiological profile of the ubiquitinated proteins within the skin, we profiled healthy skin and CYLD cutaneous syndrome (CCS) skin tumours through di-glycine remnant immunopurification proteomics, enabling identification of 1605 ubiquitin sites across 731 proteins. The healthy cutaneous ubiquitinome comprised substrate classes including keratins, S100 proteins and histones. Predictive upstream enzyme analysis ranked the most frequent E3 ligase as NEDD4, and the most frequent deubiquitinases included USP7 and CYLD. Analysis of the CCS tumor ubiquitinome, characterized by catalytically inactivated CYLD somatic mutations and prominent extracellular matrix (ECM) secretion, identified 251 differentially ubiquitinated sites compared to healthy skin. The CCS ubiquitinome was enriched for cell division and differentiation proteins, including predicted CYLD substrate insulin receptor (INSR). Secretome analysis of INSR knockdown CCS primary cells revealed reduced secretion of basement membrane proteins, particularly COL7A1. By defining how ubiquitination modulates pathophysiological ECM secretory output, our study highlights the ubiquitin post-translational system as a broader determinant of tissue architecture. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=86 SRC="FIGDIR/small/691868v1_ufig1.gif" ALT="Figure 1"> View larger version (47K): org.highwire.dtl.DTLVardef@565e59org.highwire.dtl.DTLVardef@4c3084org.highwire.dtl.DTLVardef@52a43org.highwire.dtl.DTLVardef@11999d8_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2025

p125A (Sec23ip) couples COPII coat assembly with donor-acceptor membrane organization to facilitate tunnel-based traffic.

COPII-coat proteins play a crucial role in generating small vesicles at endoplasmic reticulum (ER) exit sites (ERES). However, they also assemble at the necks of tunnels and tubules connecting the ER exit site (donor) to the ERGIC/cis-Golgi cisterna (acceptor). How can COPII support these two traffic mechanisms? Through cell-free reconstitutions, we have found that the apposition of donor and acceptor membranes is important for the assembly of the outer layer of the COPII coat (Sec13/31) but had minimal impact on Sar1-induced COPII inner layer (Sec23/24) recruitment. The expression of the adaptor protein p125A, which binds to phosphatidylinositol 4-phosphate (PI4P), Sec31 and Sec23, stabilized the contact between the donor and acceptor membranes and promoted COPII outer layer assembly. A p125A-chimera expressing a Golgi-targeted PI4P-binding domain could also support outer layer assembly. Notably, the C-terminal helical domain of Sec31A, which interacts with p125A, was essential for its assembly at ERES. In cells lacking p125A, the assembly of the COPII outer layer was selectively destabilized. Transcriptome and secretome analyses reveal selective adjustments to extracellular matrix remodeling and collagen secretion, which corresponded with selective inhibition of fibrillar collagen traffic from the ER. Thus, p125A connects the outer COPII layer at ERES with PI4P-rich ERGIC/cis-Golgi membranes, coordinating COPII assembly with tunnel-driven collagen traffic.

cell biology↗

bioRxiv2023

Endoplasmic reticulum exit sites are segregated for secretion based on cargo size

TANGO1-family proteins (TANGO1, TANGO1S and cTAGE5) form stable complexes at the Endoplasmic Reticulum Exit Sites (ERES) and mediate export of bulky cargoes. The C-terminal proline rich domain (PRD) of these proteins binds Sec23A and affects COPII assembly at ERES. These PRD interactions were replaced with light-responsive domains to control the binding between TANGO1S-DPRD and Sec23A. TANGO1S{Delta}PRD was dispersed in the ER membrane but relocated rapidly, yet reversibly, to pre-exiting ERES by binding to Sec23A upon light-activation. Prolonged binding of these two proteins concentrated ERES in the juxtanuclear region by a microtubule dependent process, blocked secretory cargo export and relocated ERGIC53 into the ER, but had limited impact on Golgi complex organization. Under these conditions, bulky collagen VII, and endogenous collagen I were collected at less than 47% of the stalled ERES, whereas small cargo molecules were halted uniformly across the ER, indicating that ERES differentially adapt to cargo size. We suggest these differences in cargo-accumulation at ERES permit cells to balance trafficking of cargoes of different sizes and optimize secretion.

cell biology↗

bioRxiv2023

A model for collagen secretion by intercompartmental continuities

Newly synthesized secretory proteins are exported from endoplasmic reticulum (ER) at specialized subcompartments called exit sites (ERES). Cargoes like procollagen are too large for export by the standard COPII-coated vesicle of 60 nm average diameter. We have previously suggested that procollagen is transported from the ER to the next secretory organelle, the ERGIC, in TANGO1-dependent inter-organelle tunnels. Here, we show that intrinsically disordered domains of TANGO1 in the ER lumen generate an entropic contraction that pulls procollagen towards the ERES. Molecular gradients of pH and HSP47 between the ER and ERGIC generate a force in the range of tens of femtoNewtons (fN), which is sufficient to propel procollagen from the ER at a speed of [~]1 nm.s-1. This calculated speed and the quantities of collagen secreted are similar to its observed physiological secretion rate in fibroblasts, consistent with the proposal that ER export is the rate limiting step for procollagen secretion. Our theoretical model explains how cells can utilize molecular gradients to export procollagens at a rate commensurate with physiological needs. Significance StatementProcollagen cannot be exported from the endoplasmic reticulum (ER) by standard COPII-coated vesicle of 60 nm average diameter. We have previously suggested that collagen is transported from the ER to the next secretory organelle, the ERGIC, in TANGO1-dependent inter-organelle tunnels. ER and ERGIC differ in molecular composition including their pH and protein composition. We propose a mechanical/entropic ratchet model whereby molecular gradients of pH and the collagen chaperone HSP47, provide the energy to propel procollagen from the ER at a speed that matches the physiological rate of collagen secretion.

biophysics↗

bioRxiv2020

GORASPs link Golgi cisternae laterally to stabilize the rims and prevent vesiculation

In vitro experiments have shown GRASP65 (GORASP1) and GRASP55 (GORASP2) proteins function in stacking Golgi cisternae. However, in vivo depletion of GORASPs in metazoans have given equivocal results. We have generated a mouse lacking both GORASPs and find that Golgi cisternae remained stacked. However, the stacks are disconnected laterally from each other and the cisternal cross-sectional diameters are significantly reduced compared to their normal counterparts. These data support earlier findings on the role of GORASPs in linking stacks and we suggest that unlinking of stacks affects dynamic control of COPI budding and vesicle fusion at the rims. The net result is that cisternal cores remain stacked, but cisternal diameter is reduced by rim consumption.

cell biology↗

bioRxiv2020

TANGO1 membrane helices create a lipid diffusion barrier at curved membranes

We have previously shown TANGO1 organises membranes at the interface of the endoplasmic reticulum (ER) and ERGIC/Golgi (Raote et al., 2018). TANGO1 corrals retrograde membranes at ER exit sites to create an export conduit. Here the retrograde membrane is, in itself, an anterograde carrier. This mode of forward transport necessitates a mechanism to prevent membrane mixing between ER and the retrograde membrane. TANGO1 has an unusual membrane helix organisation, composed of one membrane-spanning helix (TM) and another that penetrates the inner leaflet (IM). We have reconstituted these membrane helices in model membranes and shown that TM and IM together reduce the flow of lipids at a region of defined shape. We have also shown that the helices align TANGO1 around an ER exit site. We suggest this is a mechanism to prevent membrane mixing during TANGO1-mediated transfer of bulky secretory cargos from the ER to the ERGIC/Golgi via a tunnel.

cell biology↗

bioRxiv2019

Biallelic TANGO1 mutations cause a novel syndromal disease due to hampered cellular collagen secretion

The transport and Golgi organization 1 (TANGO1) family proteins have been shown to play pivotal roles in the secretory pathway. Full length TANGO1 is a transmembrane protein localised at endoplasmic reticulum exit sites (ERES), where it binds bulky cargo within the ER lumen and recruits membranes from the ER Golgi intermediate compartment (ERGIC) to create an exit route for their export. Tango1 knockout mice display a global collagen secretion defect and perinatal lethality. Here we report the first TANGO1-associated syndrome in humans, which mainly manifests in a collagenopathy. A synonymous substitution that results in exon 8 skipping in most mRNA molecules, ultimately leading to a truncated TANGO1 protein was identified as the disease-causing mutation. The four homozygously affected sons of a consanguineous family display severe dentinogenesis imperfecta, short stature, various skeletal abnormalities, insulin-dependent diabetes mellitus, sensorineural hearing loss, and mild intellectual disability. Functional studies in HeLa and U2OS cells revealed that the corresponding truncated TANGO1 protein is dispersed in the ER and its expression in cells with intact endogenous TANGO1 impairs cellular collagen I secretion.

genetics↗

bioRxiv2019

TANGO1 regulates membrane tension to mediate procollagen export

The endoplasmic reticulum (ER)-resident transmembrane protein TANGO1 assembles into a ring around COPII subunits at ER exit sites (ERES), and links cytosolic membrane-remodeling machinery, tethers, and ER-Golgi intermediate compartment (ERGIC) membranes to procollagens in the ER lumen (Raote et al., 2018). This arrangement is proposed to create a route for direct transfer of procollagens from ERES to ERGIC membranes via a tunnel. Here, we present a physical model in which TANGO1 forms a linear filament that wraps around COPII lattices at ERES to stabilize the neck of a growing transport intermediate. Importantly, our results show that TANGO1 is able to stabilize ERES-ERGIC opening by regulating ER membrane tension to allow procollagen loading and export from the ER. Altogether, our theoretical approach provides a mechanical framework of TANGO1 as a membrane tension regulator to control procollagen export from the ER.

biophysics↗