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Natural microbial communities are phylogenetically and metabolically diverse. In addition to underexplored organismal groups 1 , this diversity encompasses a rich discovery potential for ecologically and biotechnologically relevant enzymes and biochemical compounds 2 , 3 . However, studying this diversity to identify genomic pathways for the synthesis of such compounds 4 and assigning them to their respective hosts remains challenging. The biosynthetic potential of microorganisms in the open ocean remains largely uncharted owing to limitations in the analysis of genome-resolved data at the global scale. Here we investigated the diversity and novelty of biosynthetic gene clusters in the ocean by integrating around 10,000 microbial genomes from cultivated and single cells with more than 25,000 newly reconstructed draft genomes from more than 1,000 seawater samples. These efforts revealed approximately 40,000 putative mostly new biosynthetic gene clusters, several of which were found in previously unsuspected phylogenetic groups. Among these groups, we identified a lineage rich in biosynthetic gene clusters (‘ Candidatus Eudoremicrobiaceae’) that belongs to an uncultivated bacterial phylum and includes some of the most biosynthetically diverse microorganisms in this environment. From these, we characterized the phospeptin and pythonamide pathways, revealing cases of unusual bioactive compound structure and enzymology, respectively. Together, this research demonstrates how microbiomics-driven strategies can enable the investigation of previously undescribed enzymes and natural products in underexplored microbial groups and environments. Global ocean microbiome survey reveals the bacterial family ‘ Candidatus Eudoremicrobiaceae’, which includes some of the most biosynthetically diverse microorganisms in the ocean environment.

Baculovirus-infected insect cells have become a powerful tool to express recombinant proteins for structural and functional studies by NMR spectroscopy. This article provides an introduction into the insect cell/baculovirus expression system and its use for the production of recombinant isotope-labeled proteins. We discuss recent advances in inexpensive isotope-labeling methods using labeled algal or yeast extracts as the amino acid source and give examples of advanced NMR applications for proteins, which have become accessible by this eukaryotic expression host.

Naturally competent bacteria encode sophisticated protein machinery for the uptake and translocation of exogenous DNA into the cell. If this DNA is integrated into the bacterial genome, the bacterium is said to be naturally transformed. Most competent bacterial species utilise type IV pili for the initial DNA uptake step. These proteinaceous cell-surface structures are composed of thousands of pilus subunits (pilins), designated as major or minor according to their relative abundance in the pilus. Here, we show that the minor pilin FimT plays an important role in the natural transformation of Legionella pneumophila . We use NMR spectroscopy, in vitro DNA binding assays and in vivo transformation assays to understand the molecular basis of FimT’s role in this process. FimT binds to DNA via an electropositive patch, rich in arginines, several of which are well-conserved and located in a conformationally flexible C-terminal tail. FimT orthologues from other Gammaproteobacteria share the ability to bind to DNA. Our results suggest that FimT plays an important role in DNA uptake in a wide range of competent species. Many bacteria can take up exogenous DNA, in a process that often requires surface appendages composed of thousands of protein subunits called pilins. Here, Braus et al. show that a minor pilin binds directly to DNA and is important for DNA uptake in the pathogen Legionella pneumophila .

The nuclear spin-lattice relaxation rate 1/ T 1 depends on the correlation time τ c of the molecule bearing the nuclear spin, and can therefore probe changes of τ c upon binding of a rapidly moving small ligand to a more slowly moving larger protein. In practice however, the dependence is such that only a small difference in relaxation rate is obtained at high field. Here we present a scheme in which nuclear spins are first hyperpolarized using DNP, and then allowed to relax at low magnetic field in presence of a target protein, which generates a large T 1 contrast. The sample is subsequently transferred into a conventional nuclear magnetic resonance probe (NMR), where the effect of the low-field relaxation is read out using high-field liquid-state NMR. Using only 14 μM of a 13 C-labeled reporter ligand, we observe protein binding reliably for protein concentrations as low as 2 μM in a single scan. The scheme is expanded to a label-free ligand via a competitive binding experiment in which the label-free ligand displaces the 13 C-labeled reporter ligand. The nuclear spin-lattice relaxation rate can be used to probe binding of a rapidly moving small ligand to a more slowly moving larger protein, however, the measurements are challenging at high magnetic fields. Here, the authors report low-field relaxation as a sensitive contrast mechanism for detecting ligand binding, using a hyperpolarization experiment to detect ligand signals with high repeatability at concentrations as low as 14 μM.

In this work, we examine methyl nuclear magnetic resonance (NMR) spectra of the methionine ε-[13CH3] labelled thermostabilized β1 adrenergic receptor from turkey in association with a variety of different effectors, including mini-Gs and nanobody 60 (Nb60), which have not been previously studied in complex with β1 adrenergic receptor (β1AR) by NMR. Complexes with pindolol and Nb60 induce highly similar inactive states of the receptor, closely resembling the resting state conformational ensemble. We show that, upon binding of mini-Gs or nanobody 80 (Nb80), large allosteric changes throughout the receptor take place. The conformation of tβ1AR stabilized by the native-like mini-Gs protein is highly similar to the conformation induced by the currently used surrogate Nb80. Interestingly, in both cases residual dynamics are present, which were not observed in the resting states. Finally, we reproduce a pharmaceutically relevant situation, where an antagonist abolishes the interaction of the receptor with the mini-G protein in a competitive manner, validating the functional integrity of our preparation. The presented system is therefore well suited for reproducing the individual steps of the activation cycle of a G protein-coupled receptor (GPCR) in vitro and serves as a basis for functional and pharmacological characterizations of more native-like systems in the future.

Carbohydrates regulate an inimitable spectrum of biological functions, yet successfully leveraging this therapeutic avenue continues to be frustrated by low affinities with glycan-specific proteins. A conspicuous exception is the interaction of monosialotetrahexosylganglioside (GM1) with the carbohydrate-recognition domain of cholera toxin from Vibrio cholerae: this is one of the strongest protein–carbohydrate interactions known. To establish the importance of a long-discussed key hydrogen bond between C2 of the terminal galactose of GM1 and the B subunit pentamer of cholera toxin (CTB5), the total synthesis of a selectively fluorinated GM1 epitope was conducted in 19 steps. This process of molecular editing (Oδ‑H → Fδ‑) strategically deletes the hydrogen bond donor while retaining the localized partial charge of the substituent. Comparison of the binding affinity of F-GM1/CTB5 with native GM1, the GM1 carbohydrate epitope, and meta-mononitrophenyl-α-galactoside (MNPG) revealed a trend that fully supports the importance of this key interaction. These NMR data suggest that F-GM1 binds in a closely similar conformation as native GM1. Crystallographic analyses of the complex also confirm that the OH → F bioisosteric exchange at C2 of the terminal galactose induces a ring conformation that eliminates key hydrogen bonds: these interactions are compensated for by inter- and intramolecular fluorine-specific interactions.

The NMR structure of the recombinant elk prion protein (ePrP), which represents the cellular isoform ( ePrPC) in the healthy organism, is described here. As anticipated from the highly conserved amino acid sequence, ePrPChas the same global fold as other mammalian prion proteins (PrPs), with a flexibly disordered \"tail\" of residues 23-124 and a globular domain 125-226 with three α-helices and a short antiparallel β-sheet. However, ePrPCshows a striking local structure variation when compared with most other mammalian PrPs, in particular human, bovine, and mouse PrPC. A loop of residues 166-175, which links the β-sheet with the α2-helix and is part of a hypothetical \"protein X\" epitope, is outstandingly well defined, whereas this loop is disordered in the other species. Based on NMR structure determinations of two mouse PrP variants, mPrP[N174T] and mPrP[S170N,N174T], this study shows that the structured loop in ePrPCrelates to these two local amino acid exchanges, so that mPrP[S170N,N174T] exactly mimics ePrPC. These results are evaluated in the context of recent reports on chronic wasting disease (CWD) in captive and free-ranging deer and elk in the U.S. and Canada, and an animal model is proposed for support of future research on CWD.

Responses from G protein-coupled receptors (GPCRs) are downregulated in a precisely orchestrated process called desensitization. This process consists of two major steps: phosphorylation of the receptor by GPCR kinases (GRKs), predominantly on its C-terminus, and recruitment of arrestin, resulting in different signaling outcomes. Yet, it remains unclear how the phosphorylation pattern on the receptor is determined. We carried out an NMR-based study of the phosphorylation patterns generated by GRK1 and GRK2 on C-terminal peptides of selected receptors (rhodopsin for GRK1, and β 1 - and β 2 -adrenergic receptors (ARs) for GRK2). Our data reveal that the kinases are promiscuous with respect to the substrate peptide, but produce clearly defined phosphorylation patterns on each substrate. We found pronounced differences in the rates at which certain residues are phosphorylated, in particular in the PXPP motifs in rhodopsin and β 1 AR. These results show that GRKs produce well-defined phosphorylation patterns in absence of further modulators like the full receptor or Gβγ, and that the time profile of the phosphorylation barcode seems to be largely encoded in the minimal pair of C-terminal peptide and GRK. The data further suggest that arrestin might encounter different phosphorylation barcodes over time, hinting at the possibility of time-dependent arrestin responses. The investigation of GPCR C-terminal phosphorylation reveals inherent specificity of GRKs. The time-resolved NMR data hint at the possibility of time-dependent downstream signaling.

RAS mutations lead to a constitutively active oncogenic protein that signals through multiple effector pathways. In this chemical biology study, we describe a novel coupled biochemical assay that measures activation of the effector BRAF by prenylated KRASG12V in a lipid-dependent manner. Using this assay, we discovered compounds that block biochemical and cellular functions of KRASG12V with low single-digit micromolar potency. We characterized the structural basis for inhibition using NMR methods and showed that the compounds stabilized the inactive conformation of KRASG12V. Determination of the biophysical affinity of binding using biolayer interferometry demonstrated that the potency of inhibition matches the affinity of binding only when KRAS is in its native state, namely post-translationally modified and in a lipid environment. The assays we describe here provide a first-time alignment across biochemical, biophysical, and cellular KRAS assays through incorporation of key physiological factors regulating RAS biology, namely a negatively charged lipid environment and prenylation, into the in vitro assays. These assays and the ligands we discovered are valuable tools for further study of KRAS inhibition and drug discovery.

Fluorine NMR has recently gained high popularity in drug discovery as it allows efficient and sensitive screening of large numbers of ligands. However, the positive hits found in screening must subsequently be ranked according to their affinity in order to prioritize them for follow-up chemistry. Unfortunately, the primary read-out from the screening experiments, namely the increased relaxation rate upon binding, is not proportional to the affinity of the ligand, as it is polluted by effects such as exchange broadening. Here we present the method CSAR (Chemical Shift-anisotropy-based Affinity Ranking) for reliable ranking of fluorinated ligands by NMR, without the need of isotope labeled protein, titrations or setting up a reporter format. Our strategy is to produce relaxation data that is directly proportional to the binding affinity. This is achieved by removing all other contributions to relaxation as follows: (i) exchange effects are efficiently suppressed by using high power spin lock pulses, (ii) dipolar relaxation effects are approximately subtracted by measuring at two different magnetic fields and (iii) differences in chemical shift anisotropy are normalized using calculated values. A similar ranking can be obtained with the simplified approach FastCSAR that relies on a measurement of a single relaxation experiment at high field (preferably > 600 MHz). An affinity ranking obtained in this simple way will enable prioritizing ligands and thus improve the efficiency of fragment-based drug design.