Biology subjects

Langosch, D.

Publications and source records attributed to Langosch, D..

4 recordsLinked to original sources

bioRxiv2026

Transmembrane-domain-driven heterodimer assembly licenses integrin head-domain folding in the endoplasmic reticulum

Integrins are a large family of /{beta} heterodimeric receptors whose activation is associated with the extension of the ectodomain and disruption of transient transmembrane domain (TMD) interactions. Whether the TMD interaction serves additional function(s) beyond regulating integrin activation remains unclear. Here, we report that three TMD-disruptive mutations within the integrin {beta}1-subunit activate its function while simultaneously reducing its surface expression. While a Gly744Asn ({beta}1-GN) and Gly744Leu ({beta}1-GL) TMD mutation yielded viable homozygous offspring, the more disruptive Leu748Arg ({beta}1-LR) TMD mutation caused embryonic lethality in mice and drastically reduced {beta}1-integrin surface levels. Cell biology and biochemistry studies revealed that TMD-TMD interactions drive efficient /{beta}-heterodimer assembly, thereby enabling the coupled folding of the ER-luminal {beta}I-domain. Disruption of these TMD interactions leads to endoplasmic reticulum (ER) retention and luminal domain-dependent ER-associated degradation of the monomeric, misfolded {beta}1-subunit. Moreover, mutations that disrupt the /{beta} TMD interaction of multiple integrin classes in humans similarly impair integrin cell surface expression and cause severe loss-of-function diseases. Together, our findings establish that /{beta} TMD association serves a previously unrecognized role in integrin biogenesis by promoting {beta}I-domain folding, preventing premature integrin activation in the ER, and ensuring the proper cell surface expression of activatable integrins.

cell biology↗

bioRxiv2018

Stabilization / destabilization of the APP transmembrane domain by mutations in the di-glycine hinge alter helical structure and dynamics, and impair cleavage by γ-secretase

Intramembrane cleavage of the {beta}-amyloid precursor protein C99 substrate by {gamma}-secretase is implicated in Alzheimers disease pathogenesis. Since conformational flexibility of a di-glycine hinge in the C99 transmembrane domain (TMD) might be critical for {gamma}-secretase cleavage, we mutated one of the glycine residues, G38, to a helix-stabilizing leucine and to a helix-distorting proline. CD, NMR and hydrogen/deuterium exchange measurements as well as MD simulations showed that the mutations distinctly altered the intrinsic structural and dynamical properties of the TMD. However, although helix destabilization/unfolding was not observed at the initial {varepsilon}-cleavage sites of C99, both mutants impaired {gamma}-secretase cleavage and altered its cleavage specificity. Moreover, helix flexibility enabled by the di-glycine hinge translated to motions of other helix parts. Our data suggest that both local helix stabilization and destabilization in the di-glycine hinge may decrease the occurrence of enzyme-substrate complex conformations required for normal catalysis and that hinge mobility can be conducive for productive substrate-enzyme interactions.

biophysics↗

bioRxiv2018

Increased γ-Site H-Bond Stability Relates to Altered ε-Efficiency and Aβ Levels in the I45T Familial Alzheimer’s Disease Mutant of APP

Cleavage of the amyloid precursor proteins (APP) transmembrane domain (TMD) by {gamma}-secretase is a crucial step in the aetiology of Alzheimers Disease (AD). Mutations in the APP TMD alter cleavage and lead to familial forms of AD (FAD). The majority of FAD mutations shift the preference of initial cleavage from {varepsilon}49 to {varepsilon}48, thus raising the AD-related A{beta}42/A{beta}40 ratio. The I45T mutation is among the few FAD mutations that do not alter {varepsilon}-site preference, while it dramatically reduces the efficiency of {varepsilon}-cleavage. Here, we investigate the impact of the I45T mutation on the backbone dynamics of the substrate TMD. Amide exchange experiments and molecular dynamics simulations in solvent and a lipid bilayer reveal an increased stability of amide hydrogen bonds at the {zeta}-and {gamma}-cleavage sites. Stiffening of the H-bond network is caused by an additional H-bond between the T45 side chain and the TMD backbone, which alters dynamics within the cleavage domain. In particular, the increased H-bond stability inhibits an upward movement of the {varepsilon}-sites in the I45T mutant. Thus, an altered presentation of {varepsilon}-sites to the active site of {gamma}-secretase as a consequence of restricted local flexibility provides a rationale for reduced {varepsilon}-cleavage efficiency of the I45T mutant.

biophysics↗

bioRxiv2018

Metastable XBP1u transmembrane domain mediates insertion into the ER membrane and intramembrane proteolysis by the signal peptide peptidase

Unspliced XBP1 mRNA encodes XBP1u, the transcriptionally inert variant of the unfolded protein response (UPR) transcription factor XBP1s. XBP1u targets its mRNA-ribosome-nascent-chain-complex to the endoplasmic reticulum (ER) to facilitate UPR activation and prevents overactivation. Yet, its membrane association is controversial. Here, we use cell-free translocation and cellular assays to define a moderately hydrophobic stretch in XBP1u that is sufficient to mediate insertion into the ER membrane. Mutagenesis of this transmembrane (TM) region reveals residues that facilitate XBP1u turnover by an ER-associated degradation route that is dependent on signal peptide peptidase (SPP). Furthermore, the impact of these mutations on TM helix dynamics was assessed by residue-specific amide exchange kinetics, evaluated by a semi-automated algorithm. Based on our results, we suggest that SPP-catalyzed intramembrane proteolysis of TM helices is not only determined by their conformational flexibility, but also by side chain interactions near the scissile peptide bond with the enzymes active site.

cell biology↗