Biology subjects

Sternke-Hoffmann, R.

Publications and source records attributed to Sternke-Hoffmann, R..

3 recordsLinked to original sources

bioRxiv2025

Protein-Driven Copper Redox Regulation: Uncovering the Role of Disulphide Bonds and Allosteric Modulation

Copper plays essential roles in enzymatic activity, redox reactions, and cellular signalling, but becomes toxic when redox homeostasis is disrupted. While Cu(II) reduction is commonly attributed to unfolded or amyloid proteins, here we show that the well-folded plasma protein human serum albumin (HSA) intrinsically reduces Cu(II) to Cu(I) in the absence of external reductants. Using X-ray absorption spectroscopy (XAS), small-angle X-ray scattering (SAXS), circular dichroism (CD) and computational modelling (QM/MM and DFT), we identify a redox mechanism involving the disulphide bond Cys392-Cys438 in domain III of HSA. Cu binding at the high-affinity ATCUN motif triggers conformational changes that expose this disulphide bond, enabling thiol-mediated electron transfer and Cu(I) formation. Chelation with tetrathiomolybdate (TTM) impairs this reduction by restricting access to the reactive disulphide site. Comparative analysis with other globular proteins reveals that Cu reduction requires both accessible disulphide motifs and a native folded structure. Simulations and spectroscopy of SOD1 confirm that disulphide cleavage enhances Cu-thiolate interaction, supporting a generalizable two-site redox mechanism. These findings reveal a previously unrecognized mode of protein-mediated copper reduction and suggest broader physiological roles for disulphide-regulated redox switching in metal homeostasis.

biochemistry↗

bioRxiv2024

Phase Separation and Aggregation of α-Synuclein Diverge at Different Salt Conditions

The coacervation and structural rearrangement of the protein alpha-synuclein (Syn) into cytotoxic oligomers and amyloid fibrils are considered pathological hallmarks of Parkinsons disease. While aggregation is recognized as the key element of amyloid diseases, liquid-liquid phase separation (LLPS) and its interplay with aggregation have gained increasing interest. Previous work showed that factors promoting or inhibiting amyloid formation have similar effects on phase separation. Here, we provide a detailed scanning of a wide range of parameters including protein, salt and crowding concentrations at multiple pH values, revealing different salt dependencies of aggregation and phase separation. The influence of salt on aggregation under crowded conditions follows a non-monotonic pattern, showing increased effects at medium salt concentrations. This behavior can be elucidated through a combination of electrostatic screening and salting-out effects on the intramolecular interactions between the N-terminal and C-terminal regions of Syn. By contrast, we find a monotonic salt dependence of phase separation due to the intermolecular interaction. Furthermore, we observe the time evolution of the two distinct assembly states, with macroscopic fibrillar-like bundles initially forming at medium salt concentration but subsequently converting into droplets after prolonged incubation. The droplet state is therefore capable of inhibiting aggregation or even dissolving the aggregates through a variety of heterotypic interactions, thus preventing Syn from its dynamically arrested state.

biophysics↗

bioRxiv2021

Universal amyloidogenicity of patient-derivedimmunoglobulin light chains

The deposition of immunoglobulin light chains (IgLCs) in the form of amorphous aggregates or amyloid fibrils in different tissues of patients can lead to severe and potentially fatal organ damage, requiring transplantation in some cases. There has been great interest in recent years to elucidate the origin of the very different in vivo solubilities of IgLCs, as well as the molecular determinants that drive either the formation of ordered amyloid fibrils or disordered amorphous aggregates. It is commonly thought that the reason of this differential aggregation behaviour is to be found in the amino acid sequences of the respective IgLCs, i.e. that some sequences display higher intrinsic tendencies to form amyloid fibrils. Here we perform in depth Thermodynamic and Aggregation Fingerprinting (ThAgg-Fip) of 9 multiple myeloma patient-derived IgLCs, the amino acid sequences of all of which we have solved by de novo protein sequencing with mass spectrometry. The latter technique was also used for one IgLc from a patient with AL amyloidosis. We find that all samples also contain proteases that fragment the proteins under physiologically relevant mildly acidic pH conditions, leading to amyloid fibril formation in all cases. Our results suggest that while every pathogenic IgLC has a unique ThAgg fingerprint, all sequences have comparable amyloidogenic potential. Therefore, extrinsic factors, in particular presence of, and susceptibility to, proteolytic cleavage is likely to be a strong determinant of in vivo aggregation behaviour. The important conclusion, which is corroborated by systematic analysis of our sequences, as well as many sequences of IgLCs from amyloidosis patients reported in the literature, challenges the current paradigm of the link between sequence and amyloid fibril formation of pathogenic light chains.

biophysics↗