Speaker: Dr. Alexander von Appen, Research Group Leader, Max Planck Institute of Molecular Cell Biology and Genetics Dresden

Title: “Building a minimal nucleus to understand structure and mechanics of assembly”

Date: Tuesday, 16 June 2026

Time: 13:00

Room: B CUBE E73 + E74, Tatzberg 41, 01307 Dresden

Host: Research Training Group Biomolecular Condensates (RTG 3120)

Abstract: The nucleus, the largest organelle in human cells, plays a crucial role in protecting, organizing, and regulating our genome. Despite its complexity, it undergoes remarkable dynamics during cell division: as the cell enters mitosis, nuclear organization dissolves, leading to the detachment of the nuclear membrane from chromatin. The nucleoplasm and cytoplasm merge into a single entity, while the spindle distributes chromosomes to form daughter cells. Following this “open” mitosis, the entire organelle reassembles within minutes, prompting the central question: what molecular mechanisms drive nuclear self-assembly?

I will present our latest efforts to reconstitute nuclear self-assembly processes, which we study structurally using cryo-electron tomography and mechanically using optical tweezers. Specifically, I will show how ESCRT proteins assemble to close the nuclear membrane and how DNA is organized at the chromatin–nuclear membrane interface.

Speaker: Prof. Dr. Arash Nikoubashman, Professor, Theory of Biologically Inspired Polymers, Leibniz Institute of Polymer Research Dresden

Title: “Molecular insights into biomolecular condensates from coarse-grained simulations”

Date: Tuesday, 02 June 2026

Time: 12:00

Room: Left Auditorium, CRTD, Fetscherstrasse 105, 01307 Dresden

Host: Research Training Group Biomolecular Condensates (RTG 3120)

Abstract: Biomolecular condensates are essential to cellular processes and organization, and are formed by weak, multivalent interactions among biomolecules, such as intrinsically disordered proteins (IDPs). Leveraging the conceptual parallels between IDPs and classical polymers, physics-based theories and molecular simulations provide powerful tools to unravel their structural and dynamic properties. Using this approach, we show that IDPs within condensates typically adopt swollen, coil-like configurations that gradually collapse as the chains transition from the dense core, through the interface, into the surrounding aqueous phase. Beyond the intrinsic organization of the IDPs themselves, we demonstrate that small-molecule cosolutes such as ATP can modulate the phase separation of IDPs and reshape the morphology of the condensed phase, e.g., from core-shell to dewetted architectures. This structural richness is mirrored by an equally rich dynamical behavior. Through a systematic analysis of model proteins built from negatively charged glutamic acid and positively charged lysine residues, we uncover a universal correlation between microscopic contact dynamics and mesoscopic material properties as the sequence charge pattern is varied: with increasing charge segregation, the diffusion coefficient of the chains within the dense phase decreases, while both the dense-phase viscosity and the condensate-water surface tension increase.

Speaker: Dr. Lars Hubatsch, Postdoctoral Researcher, Max Planck Institute of Molecular Cell Biology and Genetics Dresden

Title: “Transport Kinetics Across Phase Boundaries”

Date: Tuesday, 19 May 2026

Time: 12:00

Room: Left Auditorium, CRTD, Fetscherstrasse 105, 01307 Dresden

Host: Research Training Group Biomolecular Condensates (RTG 3120)

Abstract: Biomolecular condensates organize intracellular chemistry, but to do so they must exchange molecules across their boundaries. I will discuss our theoretical and experimental work on the kinetics of transport across interfaces in phase-separated systems. We developed a non-equilibrium thermodynamic description of both interface motion and molecular exchange, linking single-molecule behavior to bulk transport. In the thin-interface limit, breaking local equilibrium generates an interfacial transport resistance, and I will give a physical picture for where this resistance comes from. Finally, I will present recent experiments in reconstituted condensates that support the existence of interface resistance and show how it can be measured, with direct consequences for exchange kinetics and therefore potential functions.

Speaker: Patrick McCall, Independent Research Associate, Division of Polymer Biomaterials Science, Max Bergmann Center, Leibniz Institute of Polymer Research Dresden

Title: “Contrasting phases: from biomolecular composition to condensate properties and functionality”

Date: Tuesday, 05 May 2026

Time: 12:00

Room: Left Auditorium, CRTD, Fetscherstrasse 105, 01307 Dresden

Host: Research Training Group Biomolecular Condensates (RTG 3120)

Abstract: Biomolecular condensates are dense phases enriched in specific molecules and their complex composition underlies their physical properties as well as their contribution to essential physiological processes. Reconstitution of minimal model systems from purified components is a powerful tool to handle this complexity but doesn’t provide control of local composition directly, as a condensate’s composition is itself an emergent property governed by a complex mix of entropic effects and molecular interactions. The loss of compositional control upon phase separation is most acute in multicomponent systems, as the local component stoichiometry need not reflect the average specified by an experimenter.

In this talk, I will describe how the composition of multicomponent condensates can be measured using a label-free method we developed recently based on the analysis of tie-lines and refractive index (ATRI). I will show how precise compositional measurements across a range of model systems reveal sequence-encoded variation in physical properties for RNA-binding protein (RBP) condensates, a decoupling transition between local RNA/RBP stoichiometry and density, and how local density can regulate enzymatic reactions in peptide/ribozyme condensates. Finally, I will also discuss how couplings between distinct aspects of composition, from density and stoichiometry to local charge content and pH, provide a useful basis for contrasting condensate microenvironments and potentially for interpreting their functional consequences for regulating biochemistry.