Bettina Böttcher

The clinical efficacy of dexamethasone (DEX) in ocular therapy remains limited by its low aqueous solubility and restricted epithelial permeability. To address these limitations, we developed high-capacity micellar formulations by a modified thin-film hydration method utilizing two poly(2-oxazoline) (POx)-based ABA triblock copolymers (A-pBuOx-A and A-pPentOx-A). We achieved drug loading capacities of up to 33 wt.%. The DEX loaded nanoformulations were characterized by differential scanning calorimetry and powder X-ray diffraction confirming the amorphous nature of DEX in lyophilized formulations. The micelles had a hydrodynamic diameter of Dh ≈ 18−24 nm. Both polymers were well tolerated and did not show any toxicity in primary human conjunctival fibroblasts and epithelial cells up to 50 g/L. Furthermore, the A-pBuOx-A/DEX formulation increased the apparent permeability of DEX approximately 12.2-fold across a primary human conjunctival epithelial barrier compared with Dexa EDO, without evidence of compromised barrier integrity or cell viability. These findings establish the POx polymer platform as a promising approach for enhancing epithelial delivery of poorly water-soluble ophthalmic drugs.

Mechanosensitive channels of large conductance (MscL) are essential bacterial safety valves that prevent osmotic lysis by releasing solutes in response to membrane tension. Despite extensive functional studies on Escherichia coli MscL (EcMscL), its high-resolution structure remained unknown. Using cryo-electron microscopy, we present an experimental structure of EcMscL reconstituted in nanodiscs at 3.1 Å resolution. The structure reveals a pentameric assembly with a narrow hydrophobic gate at the cytosolic side and a periplasmic cavity, consistent with the canonical MscL-fold. Differences to earlier published crystal structures of MscL from other organisms are in the less conserved periplasmic loop. We observe a previously unreported dimeric association of EcMscL pentamers, mediated by residues 61-63 in the periplasmic loop. This dimeric interface is located at the periplasmic side and provides a structural basis for the formation of higher-order clusters. The observed arrangement enables a fluid-like, mosaic packing of channels with center-to-center distances of 5.9–9 nm, consistent with biophysical and imaging data. These findings provide a structural framework for understanding cluster organization of EcMscL that modulates its activity in cellular stress response.

Gephyrin, the principal scaffolding protein of inhibitory postsynaptic densities, clusters glycine and GABA _A receptors via multivalent interactions. It features structured N and C terminal domains connected by an intrinsically disordered linker. Although the structural and functional properties of its terminal domains are well characterized, the mechanism by which full-length gephyrin organizes into higher-order complexes remains unresolved. Here, we combine biochemical reconstitution, cryo-electron microscopy, and mutational analyses to elucidate the structural logic of gephyrin oligomerization. We demonstrate that gephyrin adopts a stable dimeric assembly which constitutes the basic unit for both linear and oblique tetramers as well as linear hexameric arrangements. High resolution structures reveal a critical segment of the flexible linker that adopts two distinct conformations, one of which occludes the receptor-binding site. This segment harbors key phosphorylation sites, suggesting a regulatory control mechanism. Our findings redefine the architecture of inhibitory postsynaptic sites and reconcile gephyrin oligomerization models with published in-situ postsynaptic densities characterized by cryo-electron tomography.

Proteins of the Drosophila behaviour/human splicing (DBHS) family are involved in many aspects of gene regulation and maintenance like transcription, splicing and DNA repair. DBHS proteins form obligate homo- and heterodimers through interactions within a globular domain and can further dynamically oligomerise through α-helical coiled-coils, which is crucial for many functions. While the atomic structures of the dimers are established, the arrangement in higher oligomers is unknown. Here we present the structure of a filamentous NONO/SFPQ heterooligomer resolved by cryo-EM. The filaments form a double helix which is stabilized by an interdigitating network of coiled-coil interactions.

A neutral block copolymer interacted with DNA oligomers and solubilized them in nonpolar solvents. This approach allowed for reacting DNA-tagged substrates by isocyanide multicomponent reactions with broad scope and excellent yields.

Gephyrin is the principal scaffolding protein of inhibitory postsynaptic densities, clustering glycine and GABA _A receptors via multivalent interactions. It features structured N and C terminal domains connected by an intrinsically disordered linker. Although the structural and functional properties of its terminal domains are well characterized, the mechanism by which full-length gephyrin organizes into higher-order complexes remains unresolved. Here, we combine biochemical reconstitution, cryo-electron microscopy, and mutational analyses to elucidate the structural logic of gephyrin oligomerization. We demonstrate that gephyrin adopts a stable dimeric assembly which constitutes the basic unit for both linear and oblique tetramers as well as linear hexameric arrangements. High resolution structures reveal a critical segment of the flexible linker that adopts two distinct conformations, one of which occludes the receptor-binding site. This segment harbors key phosphorylation sites, providing a mechanistic link between structural conformation and regulatory control. Our findings redefine the architecture of inhibitory synapses and reconcile gephyrin oligomerization models with published in-situ post-synaptic densities characterized by cryo-electron tomography.

Osmotically varying environments are challenging for bacterial cells. Sudden drops in osmolytes cause an increased membrane tension and rupture the cells in the absence of protective mechanisms. One family of protective proteins are mechanosensitive channels of small conductance that open in response to membrane tension. Although these channels have a common architecture, they vary widely in the number of transmembrane helices, conductivity, and gating characteristics. Although there are various structures of channels in the open and closed state, the underlying common principles of the gating mechanism remain poorly understood. Here we show that YnaI opens by radial relocation of the transmembrane sensor paddles together with a shortening of the pore, which contrasts the prototypic smaller MscS. A chimera of both channels with the YnaI sensor paddles and the pore containing C-terminal part of MscS is functional and has the tension response of the paddle donor. Our research shows that elements with different structural opening mechanisms can be mixed and matched within one channel as long as they support the common area expansion on the periplasmic side.

Membrane transporters and channels are generally assumed to be based on distinct structural and functional principles. SLC26A11, a solute carrier with high expression levels in the brain, has been proposed to function as either an anion transporter or a channel. Here, we resolve this apparent discrepancy by demonstrating that SLC26A11 is a dual-function protein capable of operating as both a sulfate transporter and a chloride channel. By resolving its structure and combining biochemical studies and molecular dynamics simulations, we show that SLC26A11 exhibits all the hallmarks of a secondary transporter. The mechanistic basis for its selective ion transport identifies the protein as the elusive lysosomal sulfate exporter. Additionally, we demonstrate that SLC26A11 exhibits an uncoupled, channel-like chloride conductance gated by proton:sulfate symport. Our finding that the chloride-conducting state arises from the transport cycle may contribute to the development of novel therapeutic strategies for treating brain edema, and the identification of its role in lysosome sulfate efflux may provide new approaches to study and treat lysosomal storage diseases.

Lymphostatin is a key virulence factor of enteropathogenic and enterohaemorrhagic Escherichia coli, playing roles in bacterial colonisation of the gut and in the inhibition of lymphocyte proliferation and proinflammatory responses. The protein’s glycosyltransferase and cysteine protease motifs are required for activity against lymphocytes, but high-resolution structural information has proven elusive. Here, we describe the structure of lymphostatin from enteropathogenic E. coli O127:H6, determined by electron cryo-microscopy at different pH values. We observe three conformations of a highly complex molecule with two glycosyltransferase domains, one PaToxP-like protease domain, an ADP-ribosyltransferase domain, a vertex domain and a delivery domain. Long linkers hold these domains together and occlude the catalytic sites of the N-terminal glycosyltransferase and protease domains. Lymphostatin binds to bovine T-lymphocytes and HEK-293T cells, forming clusters at the plasma membrane that are internalized. With six distinct domains, lymphostatin can be regarded as a multitool of pathogenic Escherichia coli, enabling complex interactions with host cells.