Visualizing the disordered nuclear transport machinery in situ

The approximately 120 MDa mammalian nuclear pore complex (NPC) acts as a gatekeeper for the transport between the nucleus and cytosol1. The central channel of the NPC is filled with hundreds of intrinsically disordered proteins (IDPs) called FG-nucleoporins (FG-NUPs)2,3. Although the structure of the NPC scaffold has been resolved in remarkable detail, the actual transport machinery built up by FG-NUPs—about 50 MDa—is depicted as an approximately 60-nm hole in even highly resolved tomograms and/or structures computed with artificial intelligence4,5,6,7,8,9,10,11. Here we directly probed conformations of the vital FG-NUP98 inside NPCs in live cells and in permeabilized cells with an intact transport machinery by using a synthetic biology-enabled site-specific small-molecule labelling approach paired with highly time-resolved fluorescence microscopy. Single permeabilized cell measurements of the distance distribution of FG-NUP98 segments combined with coarse-grained molecular simulations of the NPC allowed us to map the uncharted molecular environment inside the nanosized transport channel. We determined that the channel provides—in the terminology of the Flory polymer theory12—a ‘good solvent’ environment. This enables the FG domain to adopt expanded conformations and thus control transport between the nucleus and cytoplasm. With more than 30% of the proteome being formed from IDPs, our study opens a window into resolving disorder–function relationships of IDPs in situ, which are important in various processes, such as cellular signalling, phase separation, ageing and viral entry

Reliability and accuracy of single-molecule FRET studies for characterization of structural dynamics and distances in proteins

Single-molecule Förster-resonance energy transfer (smFRET) experiments allow the study of biomolecular structure and dynamics in vitro and in vivo. We performed an international blind study involving 19 laboratories to assess the uncertainty of FRET experiments for proteins with respect to the measured FRET efficiency histograms, determination of distances, and the detection and quantification of structural dynamics. Using two protein systems with distinct conformational changes and dynamics, we obtained an uncertainty of the FRET efficiency ≤0.06, corresponding to an interdye distance precision of ≤2 Å and accuracy of ≤5 Å. We further discuss the limits for detecting fluctuations in this distance range and how to identify dye perturbations. Our work demonstrates the ability of smFRET experiments to simultaneously measure distances and avoid the averaging of conformational dynamics for realistic protein systems, highlighting its importance in the expanding toolbox of integrative structural biology

Genetic code expansion for multiprotein complex engineering

We present a baculovirus-based protein engineering method that enables site-specific introduction of unique functionalities in a eukaryotic protein complex recombinantly produced in insect cells. We demonstrate the versatility of this efficient and robust protein production platform, \u2018MultiBacTATAG\u2019, (i) for the fluorescent labeling of target proteins and biologics using click chemistries, (ii) for glycoengineering of antibodies, and (iii) for structure\u2013function studies of novel eukaryotic complexes using single-molecule F\uf6rster resonance energy transfer as well as site-specific crosslinking strategies

High resolution standing-wave surface plasmon-resonance fluorescence microscopy using optical vortices

162 p.Studies of the dynamical process of biological samples always require realtime imaging microscopy which can provide wide-field high resolution with sufficient material contrast. Therefore, fluorescence-based microscopy has become one of the essential tools of modern biology. However, like all forms of optical tool, it suffers from the fundamental limitation of the wave-nature of electromagnetic waves. While resolution is denoted by the ability to discern different objects, much effort has been devoted to improve the spatial resolution of far-field fluorescence microscopy and it has spurred the emergence of many innovative techniques.Doctor of Philosophy (EEE

Monomeric Huntingtin Exon 1 Has Similar Overall Structural Features for Wild-Type and Pathological Polyglutamine Lengths

Huntington’s disease is caused by expansion of a polyglutamine (polyQ) domain within exon 1 of the huntingtin gene (Httex1). A popular hypothesis is that the Httex1 protein undergoes sharp conformational changes as the polyQ length exceeds a threshold of 36 residues. We test this hypothesis by combining novel semi-synthesis strategies with state-of-the-art single molecule Förster resonance energy transfer measurements on biologically relevant Httex1 proteins of five different polyQ lengths. Our results, integrated with atomistic simulations, negate the hypothesis of a sharp, polyQ length-dependent change in the structure of monomeric Httex1. Instead, they support a continuous global compaction with increasing polyQ length and this derives from increased prominence of the globular polyQ domain. More specifically, we show that that monomeric Httex1 adopts tadpole-like architectures for polyQ lengths above and beyond the pathological threshold. Additionally, our results suggest that higher order homo- and / or heterotypic interactions within distinct sub-populations of neurons are likely to be the main source of sharp polyQ length-dependencies of HD. These findings pave the way for uncovering the true structural basis of Httex1-mediated neurotoxicity