A fragment screen of a library of 560 commercially available fragments using a kinetic assay identified a small molecule that increased the activity of the fungal glycoside hydrolase TrBgl2. An analogue by catalogue approach and detailed kinetic analysis identified improved compounds that behaved as nonessential activators with up to a 2-fold increase in maximum activation. The compounds did not activate the related bacterial glycoside hydrolase CcBglA demonstrating specificity. Interestingly, an analogue of the initial fragment inhibits both TrBgl2 and CcBglA, apparently through a mixed-model mechanism. Although it was not possible to determine crystal structures of activator binding to 55 kDa TrBgl2, solution NMR experiments demonstrated a specific binding site for the activator. A partial assignment of the NMR spectrum gave the identity of the amino acids at this site, allowing a model for TrBgl2 activation to be built. The activator binds at the entrance of the substrate-binding site, generating a productive conformation for the enzyme–substrate complex.

In the original publication of the article, the name of one of the authors is incorrect. The author's name is Eiso AB, but was modified to A. B. Eiso. The correct name is given in this Correction.

β-glucosidases have received considerable attention due to their essential role in bioethanol production from lignocellulosic biomass. β-glucosidase can hydrolyse cellobiose in cellulose degradation and its low activity has been considered as one of the main limiting steps in the process. Large-scale conversions of cellulose therefore require high enzyme concentration which increases the cost. β-glucosidases with improved activity and thermostability are therefore of great commercial interest. The fungus Trichoderma reseei expresses thermostable cellulolytic enzymes which have been widely studied as attractive targets for industrial applications. Genetically modified β-glucosidases from Trichoderma reseei have been recently commercialised. We have developed an approach in which screening of low molecular weight molecules (fragments) identifies compounds that increase enzyme activity and are currently characterizing fragment-based activators of TrBgl2. A structural analysis of the 55 kDa apo form of TrBgl2 revealed a classical (α/β)8-TIM barrel fold. In the present study we present a partial assignment of backbone chemical shifts, along with those of the Ile (I)-Val (V)-Leu (L) methyl groups of TrBgl2. These data will be used to characterize the interaction of TrBgl2 with the small molecule activators.

Abstract The single‐domain GH11 glycosidase from Bacillus circulans (BCX) is involved in the degradation of hemicellulose, which is one of the most abundant renewable biomaterials in nature. We demonstrate that BCX in solution undergoes minimal structural changes during turnover. NMR spectroscopy results show that the rigid protein matrix provides a frame for fast substrate binding in multiple conformations, accompanied by slow conversion, which is attributed to an enzyme‐induced substrate distortion. A model is proposed in which the rigid enzyme takes advantage of substrate flexibility to induce a conformation that facilitates the acyl formation step of the hydrolysis reaction.

No matter the source of compounds, drug discovery campaigns focused directly on the target are entirely dependent on a consistent stream of reliable data that reports on how a putative ligand interacts with the protein of interest. The data will derive from many sources including enzyme assays and many types of biophysical binding assays such as TR-FRET, SPR, thermophoresis and many others. Each method has its strengths and weaknesses, but none is as information rich and broadly applicable as NMR. Here we provide a number of examples of the utility of NMR for enabling and providing ongoing support for the early pre-clinical phase of small molecule drug discovery efforts. The examples have been selected for their usefulness in a commercial setting, with full understanding of the need for speed, cost-effectiveness and ease of implementation.

The divisome is a large protein complex that regulates bacterial cell division and therefore represents an attractive target for novel antibacterial drugs. In this study, we report on the ligandability of FtsQ, which is considered a key component of the divisome. For this, the soluble periplasmic domain of Escherichia coli FtsQ was immobilized and used to screen a library of 1501 low molecular weight (< 300 Da), synthetic compounds for those that interact with the protein. A primary screen was performed using target immobilized NMR screening (TINS) and yielded 72 hits. Subsequently, these hits were validated in an orthogonal assay. At first, we aimed to do this using surface plasmon resonance (SPR), but the lack of positive control hampered optimization of the experiment. Alternatively, a two-dimensional heteronuclear single quantum coherence (HSQC) NMR spectrum of FtsQ was obtained and used to validate these hits by chemical shift perturbation (CSP) experiments. This resulted in the identification of three fragments with weak affinity for the periplasmic domain of FtsQ, arguing that the ligandability of FtsQ is low. While this indicates that developing high affinity ligands for FtsQ is far from straightforward, the identified hit fragments can help to further interrogate FtsQ interactions.

NMR spectroscopy is a powerful technique that can provide valuable structural information for drug discovery endeavors. Here, we discuss the strengths (and limitations) of NMR applications to structure-based drug discovery, highlighting the different levels of resolution and throughput obtainable. Additionally, the emerging field of paramagnetic NMR in drug discovery and recent developments in approaches to speed up and automate protein-observed NMR data collection and analysis are discussed.

Methyl groups are powerful probes for the analysis of structure, dynamics and function of supramolecular assemblies, using both solution- and solid-state NMR. Widespread application of the methodology has been limited due to the challenges associated with assigning spectral resonances to specific locations within a biomolecule. Here, we present Methyl Assignment by Graph Matching (MAGMA), for the automatic assignment of methyl resonances. A graph matching protocol examines all possibilities for each resonance in order to determine an exact assignment that includes a complete description of any ambiguity. MAGMA gives 100% accuracy in confident assignments when tested against both synthetic data, and 9 cross-validated examples using both solution- and solid-state NMR data. We show that this remarkable accuracy enables a user to distinguish between alternative protein structures. In a drug discovery application on HSP90, we show the method can rapidly and efficiently distinguish between possible ligand binding modes. By providing an exact and robust solution to methyl resonance assignment, MAGMA can facilitate significantly accelerated studies of supramolecular machines using methyl-based NMR spectroscopy.

Retinoblastoma-binding protein-6 (RBBP6) plays a facilitating role, through its RING finger-like domain, in the ubiquitination of p53 by Hdm2 that is suggestive of E4-like activity. Although the presence of eight conserved cysteine residues makes it highly probable that the RING finger-like domain coordinates two zinc ions, analysis of the primary sequence suggests an alternative classification as a member of the U-box family, the members of which do not bind zinc ions. We show here that despite binding two zinc ions, the domain adopts a homodimeric structure highly similar to those of a number of U-boxes. Zinc ions could be replaced by cadmium ions without significantly disrupting the structure or the stability of the domain, although the rate of substitution was an order of magnitude slower than any previous measurement, suggesting that the structure is particularly stable, a conclusion supported by the high thermal stability of the domain. A hallmark of U-box-containing proteins is their association with chaperones, with which they cooperate in eliminating irretrievably unfolded proteins by tagging them for degradation by the proteasome. Using a yeast two-hybrid screen, we show that RBBP6 interacts with chaperones Hsp70 and Hsp40 through its N-terminal ubiquitin-like domain. Taken together with the structural similarities to U-box-containing proteins, our data suggest that RBBP6 plays a role in chaperone-mediated ubiquitination and possibly in protein quality control.

An efficient way to rapidly generate protein-ligand costructures based on solution-NMR using sparse NOE data combined with selective isotope labeling is presented. A docked model of the 27 kDa N-terminal ATPase domain of Hsp90 bound to a small molecule ligand was generated using only 21 intermolecular NOEs, which uniquely defined both the binding site and the orientation of the ligand. The approach can prove valuable for the early stages of fragment-based drug discovery.

We present a strategy to solve the high-resolution structure of amyloid fibrils by solid-state NMR and use it to determine the atomic-resolution structure of the prion domain of the fungal prion HET-s in its amyloid form. On the basis of 134 unambiguous distance restraints, we recently showed that HET-s(218-289) in its fibrillar state forms a left-handed β-solenoid, and an atomic-resolution NMR structure of the triangular core was determined from unambiguous restraints only. In this paper, we go considerably further and present a comprehensive protocol using six differently labeled samples, a collection of optimized solid-state NMR experiments, and adapted structure calculation protocols. The high-resolution structure obtained includes the less ordered but biologically important C-terminal part and improves the overall accuracy by including a large number of ambiguous distance restraints.

Membrane proteins are important pharmaceutical targets, but they pose significant challenges for fragment-based drug discovery approaches. Here, we present the first successful use of biophysical methods to screen for fragment ligands to an integral membrane protein. The Escherichia coli inner membrane protein DsbB was solubilized in detergent micelles and lipid bilayer nanodiscs. The solubilized protein was immobilized with retention of functionality and used to screen 1071 drug fragments for binding using target immobilized NMR Screening. Biochemical and biophysical validation of the eight most potent hits revealed an IC(50) range of 7-200 microM. The ability to insert a broad array of membrane proteins into nanodiscs, combined with the efficiency of TINS, demonstrates the feasibility of finding fragments targeting membrane proteins.

Fragment-based drug discovery (FBD) has become a widely accepted tool that is complementary to high-throughput screening (HTS) in developing small-molecule inhibitors of pharmaceutical targets. Because a fragment campaign can only be as successful as the hit matter found, it is critical that the first stage of the process be optimized. Here the authors compare the 3 most commonly used methods for hit discovery in FBD: high concentration screening (HCS), solution ligand-observed nuclear magnetic resonance (NMR), and surface plasmon resonance (SPR). They selected the commonly used saturation transfer difference (STD) NMR spectroscopy and the proprietary target immobilized NMR screening (TINS) as representative of the array of possible NMR methods. Using a target typical of FBD campaigns, the authors find that HCS and TINS are the most sensitive to weak interactions. They also find a good correlation between TINS and STD for tighter binding ligands, but the ability of STD to detect ligands with affinity weaker than 1 mM K-D is limited. Similarly, they find that SPR detection is most suited to ligands that bind with K-D better than 1 mM. However, the good correlation between SPR and potency in a bioassay makes this a good method for hit validation and characterization studies. (Journal of Biomolecular Screening 2010:978-989)

BRCA1 C-terminal domain (BRCT)-containing proteins are found widely throughout the animal and bacteria kingdoms where they are exclusively involved in cell cycle regulation and DNA metabolism. Whereas most BRCT domains are involved in protein-protein interactions, a small subset has bona fide DNA binding activity. Here, we present the solution structure of the BRCT region of the large subunit of replication factor C bound to DNA and a model of the structure-specific complex with 5'-phosphorylated double-stranded DNA. The replication factor C BRCT domain possesses a large basic patch on one face, which includes residues that are structurally conserved and ligate the phosphate in phosphopeptide binding BRCT domains. An extra alpha-helix at the N terminus, which is required for DNA binding, inserts into the major groove and makes extensive contacts to the DNA backbone. The model of the protein-DNA complex suggests 5'-phosphate recognition by the BRCT domains of bacterial NAD(+)-dependent ligases and a nonclamp loading role for the replication factor C complex in DNA transactions.

The yeast Paf1 complex consists of Paf1, Rtf1, Cdc73, Ctr9, and Leo1 and regulates histone H2B ubiquitination, histone H3 methylation, RNA polymerase II carboxy-terminal domain (CTD) Ser2 phosphorylation, and RNA 3' end processing. We provide structural insight into the Paf1 complex with the NMR structure of the conserved and functionally important Plus3 domain of human Rtf1. A predominantly beta-stranded subdomain displays structural similarity to Dicer/Argonaute PAZ domains and to Tudor domains. We further demonstrate that the highly basic Rtf1 Plus3 domain can interact in vitro with single-stranded DNA via residues on the rim of the beta sheet, reminiscent of siRNA binding by PAZ domains, but did not detect binding to double-stranded DNA or RNA. We discuss the potential role of Rtf1 Plus3 ssDNA binding during transcription elongation.

The MutS1 protein recognizes unpaired bases and initiates mismatch repair, which are essential for high-fidelity DNA replication. The homologous MutS2 protein does not contribute to mismatch repair, but suppresses homologous recombination. MutS2 lacks the damage-recognition domain of MutS1, but contains an additional C-terminal extension: the small MutS-related (Smr) domain. This domain, which is present in both prokaryotes and eukaryotes, has previously been reported to bind to DNA and to possess nicking endonuclease activity. We determine here the solution structure of the functionally active Smr domain of the Bcl3-binding protein (also known as Nedd4-binding protein 2), a protein with unknown function that lacks other domains present in MutS proteins. The Smr domain adopts a two-layer alpha-beta sandwich fold, which has a structural similarity to the C-terminal domain of IF3, the R3H domain, and the N-terminal domain of DNase I. The most conserved residues are located in three loops that form a contiguous, exposed, and positively charged surface with distinct sequence identity for prokaryotic and eukaryotic Smr domains. NMR titration experiments and DNA binding studies using Bcl3-binding protein-Smr domain mutants suggested that these most conserved loop regions participate in DNA binding to single-stranded/double-stranded DNA junctions. Based on the observed DNA-binding-induced multimerization, the structural similarity with both subdomains of DNase I, and the experimentally identified DNA-binding surface, we propose a model for DNA recognition by the Smr domain.