Biology subjects

Brügger, B.

Publications and source records attributed to Brügger, B..

3 recordsLinked to original sources

bioRxiv2022

New motifs in Ndc1 mediating interaction with the Nup84 complex and nuclear membranes

The nuclear pore complex (NPC) embedded in the double nuclear membrane is built from ~30 different nucleoporins (Nups) in multiple copies, of which a few are integral nuclear membrane proteins. One of these transmembrane Nups is Ndc1, which is thought to play a role in interphase NPC assembly at the fused inner and outer nuclear membrane. In this study, we discovered a direct interaction of Ndc1s transmembrane domain with Nup120 and Nup133, members of the Y-complex that coats the nuclear pore membrane. In addition, we identified a so far unrecognized amphipathic helix (AH) in the C-terminal domain of Ndc1, which can bind to high curvature liposomes. When overexpressed in yeast this amphipathic motif is toxic and dramatically alters the intracellular membrane organization. Further genetic investigations revealed that Ndc1-AH functionally interacts with related motifs in the C-terminus of Nups Nup53 and Nup59, known to serve in nuclear pore membrane binding and link between NPC modules. This relationship could explain why the essential function of Ndc1 can be suppressed by deleting the amphipathic helix from Nup53. Our data indicate that nuclear membrane biogenesis dependent on a balanced ratio between amphipathic motifs in diverse nucleoporins is essential for interphase NPC biogenesis.

cell biology↗

bioRxiv2021

Intramembrane protease SPP defines a cholesterol-regulated switch of the mevalonate pathway

Intramembrane proteolysis regulates important processes such as signaling and transcriptional and posttranslational abundance control of proteins with key functions in metabolic pathways. This includes transcriptional control of mevalonate pathway genes, thereby ensuring balanced biosynthesis of cholesterol and other isoprenoids. Our work shows that, at high cholesterol levels, signal peptide peptidase (SPP) cleaves squalene synthase (SQS), an enzyme that defines the branching point for allocation of isoprenoids to the sterol and non-sterol arms of the mevalonate pathway. This intramembrane cleavage releases SQS from the membrane and targets it for proteasomal degradation. Regulation of this mechanism is achieved by the E3 ubiquitin ligase TRC8 that, in addition to ubiquitinating SQS in response to cholesterol levels, acts as an allosteric activator of SPP-catalyzed intramembrane cleavage of SQS. Cellular cholesterol levels increase in the absence of SPP activity. Hence, SPP-TRC8 mediated abundance control of SQS acts as a regulation step within the mevalonate pathway.

cell biology↗

bioRxiv2021

Cholesterol promotes both head group visibility and clustering of PI(4,5)P2 driving unconventional secretion of Fibroblast Growth Factor 2

Fibroblast Growth Factor 2 (FGF2) is a cell survival factor involved in tumor-induced angiogenesis. FGF2 is secreted through an unconventional secretory pathway based upon direct protein translocation across the plasma membrane. Here we demonstrate that both PI(4,5)P2-dependent FGF2 recruitment at the inner plasma membrane leaflet and FGF2 membrane translocation into the extracellular space are positively modulated by cholesterol in living cells. We further reveal cholesterol to enhance FGF2 binding to PI(4,5)P2-containing lipid bilayers in a fully reconstituted system. Based on extensive atomistic molecular dynamics simulations and membrane tension experiments, we propose cholesterol to modulate FGF2 binding to PI(4,5)P2 by (i) increasing head group visibility of PI(4,5)P2 on the membrane surface, (ii) increasing avidity by cholesterol-induced clustering of PI(4,5)P2 molecules triggering FGF2 oligomerization and (iii) increasing membrane tension facilitating the formation of lipidic membrane pores. Our findings have general implications for phosphoinositide-dependent protein recruitment to membranes and explain the highly selective targeting of FGF2 towards the plasma membrane, the subcellular site of FGF2 membrane translocation during unconventional secretion of FGF2.

biophysics↗