Biology subjects

Sticht, J.

Publications and source records attributed to Sticht, J..

6 recordsLinked to original sources

bioRxiv2026

Glycosaminoglycans Promote Amyloid-β Aggregation via Multivalent, pH-Dependent Interactions

Glycosaminoglycans (GAGs) are polyanionic polysaccharides that co-localize with amyloid-{beta} (A{beta}) deposits in Alzheimers disease, yet their mechanistic contribution to A{beta} aggregation remains unclear. Here, we show that GAGs function as pH-responsive electrostatic scaffolds that selectively accelerate A{beta}(1-42) aggregation under mildly acidic, endosomal conditions but not at neutral extracellular pH. Combining experimental and computational approaches, we identify protonated N-terminal histidines as key determinants of GAG binding. Weak interactions between GAGs and the charged Nterminal region of A{beta} promote conformational rearrangements that bring peptides into proximity and expose adjacent hydrophobic aggregation-prone segments, thereby facilitating peptide clustering. Kinetic analyses reveal that aggregation is enhanced in a way consistent with an apparent increase in effective peptide concentration, accelerating nucleation without altering the dominant aggregation pathway. Systematic variation of GAG chain length and sulfation level further demonstrates that aggregation enhancement requires a threshold degree of multivalency, consistent with a clustering-driven mechanism. Together, these findings establish a framework in which pH-dependent electrostatic interactions with GAGs act as molecular triggers of amyloid nucleation, providing insight into how cellular microenvironments regulate the earliest stages of Alzheimers disease pathology.

biophysics↗

bioRxiv2024

Quantitative analysis of MHC class II peptide exchange reveals pivotal role of peptide association rate

MHC-II presents antigenic peptides to T helper cells, thus shaping adaptive immune responses. Peptide loading of MHC-II in endosomes is shaped by the susceptibility of the peptide-MHC-II complex to dissociation by the catalyst HLA-DM. For a given MHC-II allotype, experimental data reveal an enormous range of HLA-DM susceptibilities of different peptides - more than five orders of magnitude. To understand the underlying mechanisms, we develop a coarse-grained kinetic model and confront it with experimental data. The model explains the observed variation of HLA-DM susceptibility with the peptide-MHC-II binding energy by an allosteric competition mechanism. Paradoxically, however, certain peptides are resistant to dissociation by HLA-DM regardless of their binding energy. Our model predicts that this resistance is linked with fast peptide association to MHC-II in the absence of HLA-DM. In sum, our data-based theoretical analysis identifies two distinct molecular mechanisms that shape antigen presentation by MHC-II.

systems biology↗

bioRxiv2024

Effective assessment of CD4+ T cell Immunodominance patterns: impact of antigen processing and HLA restriction

CD4+ T cell responses to viral infections are driven by immunodominant determinants. Accessing the peptides defining these determinants in humans is essential for advancing our understanding and potentially tuning immune responses to pathogens. State of the art methods identifying CD4+ T cell immunodominant epitopes are constrained by limitations in throughput, performance or both. Here, we leverage on the combined use of a reconstituted antigen processing system and of in silico prediction tools to query and study CD4+ T cell immunodominance of two model SARS-CoV-2 antigens. We applied this combined platform over a DRB1* panel with broad population and functional coverage to gain mechanistic insights beyond single allotypes. This approach delineates a minimalistic peptide pool (59 candidates) featuring a high immunogenic profile (similar response to 10-fold larger pools) through a representative human sample. Analysis of antigen-encoded and processing-related features on IEDB curated immunodominant peptides reveal that distinct antigen processing mechanisms apply for the Nucleocapsid and Spike model antigens. Notably, the First Bind and then cut mechanism was favored for Nucleocapsid-derived epitopes (up to 55 %), whereas the First Cut and then bind predominated for the Spike (80 %). Together, our results highlight differential processing pathways underlying CD4 T cell immunodominance for distinct viral antigens providing a mechanistic foundation to improve epitope prediction algorithms. Significance StatementEfficient access to immunodominant CD4+ T cell epitopes will inform improved peptide pool design for studying or tuning immunity towards any pathogen. Despite advances in the field, in silico epitope prediction remains error-prone and experimental efforts are logistically challenging. Epitope prediction tools are mainly focused on the identification of binding motifs while neglecting key processing steps. Considering antigen processing factors and constraints is expected to improve their performance. We describe and apply a platform for the systematic investigation of antigen processing mechanisms and how they impinge on the selection of CD4+ T cell immunodominance. Our results validate distinct immunodominant epitope selection pathways for two model antigens at the human population level.

immunology↗

bioRxiv2021

ADAPs intrinsically disordered region is an actin sponge regulating T cell motility

Intrinsically disordered proteins (IDPs) play a vital role in biological processes that rely on transient molecular compartmentation1. In T cells, the dynamic switching between migration and adhesion mandates a high degree of plasticity in the interplay of adhesion and signaling molecules with the actin cytoskeleton2,3. Here, we show that the N-terminal intrinsically disordered region (IDR) of adhesion- and degranulation-promoting adapter protein (ADAP) acts as a multipronged scaffold for G- and F-actin, thereby promoting actin polymerization and bundling. Positively charged motifs, along a sequence of at least 200 amino acids, interact with both longitudinal sides of G-actin in a promiscuous manner. These polymorphic interactions with ADAP become constrained to one side once F-actin is formed. Actin polymerization by ADAP acts in synergy with a capping protein but competes with cofilin. In T cells, ablation of ADAP impairs adhesion and migration with a time-dependent reduction of the F-actin content in response to chemokine or T cell receptor (TCR) engagement. Our data suggest that IDR-assisted molecular crowding of actin above the critical concentration defines a new mechanism to regulate cytoskeletal dynamics. The principle of IDRs serving as molecular sponges to facilitate regulated self-assembly of filament-forming proteins might be a general phenomenon.

biochemistry↗

bioRxiv2021

Target recognition in tandem WW domains: complex structures for parallel and antiparallel ligand orientation in h-FBP21 tandem WW

Protein-protein interactions often rely on specialized recognition domains, such as WW domains, which bind to specific proline-rich sequences. The specificity of these protein-protein interactions can be increased by tandem repeats, i.e. two WW domains connected by a linker. With a flexible linker, the WW domains can move freely with respect to each other. Additionally, the tandem WW domains can bind in two different orientations to their target sequences. This makes the elucidation of complex structures of tandem WW domains extremely challenging. Here, we identify and characterize two complex structures of the tandem WW domain of human formin-binding protein 21 and a peptide sequence from its natural binding partner, the core-splicing protein SmB/B. The two structures differ in the ligand orientation, and consequently also in the relative orientation of the two WW domains. We analyze and probe the interactions in the complexes by molecular simulations and NMR experiments. The workflow to identify the complex structures uses molecular simulations, density-based clustering and peptide docking. It is designed to systematically generate possible complex structures for repeats of recognition domains. These structures will help us to understand the synergistic and multivalency effects that generate the astonishing versatility and specificity of protein-protein interactions.

molecular biology↗

bioRxiv2019

The α1 subunit of the Na,K-ATPase acts upstream of PI(4,5)P2 facilitating unconventional secretion of Fibroblast Growth Factor 2 from tumor cells

Fibroblast Growth Factor 2 (FGF2) is a tumor cell survival factor that is exported from cells by an unconventional secretory pathway. This process is based on direct translocation of FGF2 across the plasma membrane. FGF2 membrane translocation depends on PI(4,5)P2-induced formation of membrane-inserted FGF2 oligomers followed by extracellular trapping of FGF2 at the outer leaflet mediated by cell surface heparan sulfate proteoglycans. Beyond the well-characterized core mechanism of FGF2 membrane translocation, the Na,K-ATPase has been proposed to play a so far unknown role in unconventional secretion of FGF2. Here, we define a direct physical interaction of FGF2 with a subdomain of the cytoplasmic part of the 1 subunit of the Na,K-ATPase. Employing NMR spectroscopy and molecular dynamics simulations, we identified two lysine residues on the molecular surface of FGF2 that are shown to be essential for its interaction with 1. In intact cells, the corresponding lysine-to-glutamate variants of FGF2 were characterized by inefficient secretion and reduced recruitment to the inner plasma membrane leaflet as shown by single molecule TIRF microscopy. Our findings suggest that 1 acts upstream of PI(4,5)P2 facilitating efficient membrane translocation of FGF2 to the cell surface of tumor cells.

biochemistry↗