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SUMMARYAdhesive type 1 pili from uropathogenicEscherichia colistrains are filamentous, supramolecular protein complexes consisting of a short tip fibrillum and a long, helical rod formed by up to several thousand copies of the major pilus subunit FimA. Here, we reconstituted the entire type 1 pilus rod assembly reactionin vitro, using all constituent protein subunits in the presence of the assembly platform FimD, and identified the so-far uncharacterized subunit FimI as an irreversible assembly terminator. We provide a complete, quantitative model of pilus rod assembly kinetics based on the measured rate constants of FimD-catalyzed subunit incorporation. The model reliably predicts the length distribution of assembled pilus rods as a function of the ratio between FimI and the main pilus subunit FimA and is fully consistent with the length distribution of membrane-anchored pili assembledin vivo. The results show that the natural length distribution of adhesive pili formed via the chaperone-usher pathway results from a stochastic chain termination reaction.

RNA helicases of the DEAH/RHA family are involved in many essential cellular processes, such as splicing or ribosome biogenesis, where they remodel large RNA–protein complexes to facilitate transitions to the next intermediate. DEAH helicases couple adenosine triphosphate (ATP) hydrolysis to conformational changes of their catalytic core. This movement results in translocation along RNA, which is held in place by auxiliary C-terminal domains. The activity of DEAH proteins is strongly enhanced by the large and diverse class of G-patch activators. Despite their central roles in RNA metabolism, insight into the molecular basis of G-patch–mediated helicase activation is missing. Here, we have solved the structure of human helicase DHX15/Prp43, which has a dual role in splicing and ribosome assembly, in complex with the G-patch motif of the ribosome biogenesis factor NKRF. The G-patch motif binds in an extended conformation across the helicase surface. It tethers the catalytic core to the flexibly attached C-terminal domains, thereby fixing a conformation that is compatible with RNA binding. Structures in the presence or absence of adenosine diphosphate (ADP) suggest that motions of the catalytic core, which are required for ATP binding, are still permitted. Concomitantly, RNA affinity, helicase, and ATPase activity of DHX15 are increased when G-patch is bound. Mutations that detach one end of the tether but maintain overall binding severely impair this enhancement. Collectively, our data suggest that the G-patch motif acts like a flexible brace between dynamic portions of DHX15 that restricts excessive domain motions but maintains sufficient flexibility for catalysis., Proceedings of the National Academy of Sciences of the United States of America, 117 (13), ISSN:0027-8424, ISSN:1091-6490

Progress in NMR in general and in biomolecular applications in particular is driven by increasing magnetic-field strengths leading to improved resolution and sensitivity of the NMR spectra. Recently, persistent superconducting magnets at a magnetic field strength (magnetic induction) of 28.2 T corresponding to 1200 MHz proton resonance frequency became commercially available. We present here a collection of high-field NMR spectra of a variety of proteins, including molecular machines, membrane proteins and viral capsids and others. We show this large panel in order to provide an overview over a range of representative systems under study, rather than a single best performing model system. We discuss both carbon-13 and proton-detected experiments, and show that in13C spectra substantially higher numbers of peaks can be resolved compared to 850 MHz while for1H spectra the most impressive increase in resolution is observed for aliphatic side-chain resonances.

The Hepatitis C virus nonstructural protein 5A (NS5A) is a membrane‐associated protein involved in multiple steps of the viral life cycle. Direct‐acting antivirals (DAAs) targeting NS5A are a cornerstone of antiviral therapy, but the mode‐of‐action of these drugs is poorly understood. This is due to the lack of information on the membrane‐bound NS5A structure. Herein, we present the structural model of an NS5A AH‐linker‐D1 protein reconstituted as proteoliposomes. We use highly sensitive proton‐detected solid‐state NMR methods suitable to study samples generated through synthetic biology approaches. Spectra analyses disclose that both the AH membrane anchor and the linker are highly flexible. Paramagnetic relaxation enhancements (PRE) reveal that the dimer organization in lipids requires a new type of NS5A self‐interaction not reflected in previous crystal structures. In conclusion, we provide the first characterization of NS5A AH‐linker‐D1 in a lipidic environment shedding light onto the mode‐of‐action of clinically used NS5A inhibitors., The membrane orientation of the hepatitis C virus NS5A protein was assessed by combining a cell‐free protein synthesis approach with highly sensitive 1H‐detected solid‐state NMR. Insertion of lipids chelated with a paramagnetic Gd3+ ion allowed to orient the protein with respect to its membrane anchor using PRE. This information allowed to propose a model for the interaction of NS5A with a direct acting antiviral.