Screening of DNA-Encoded Small Molecule Libraries inside a Living Cell.

DNA-encoded small molecule libraries (DELs) have facilitated the discovery of novel modulators of many different therapeutic protein targets. We report the first successful screening of a multimillion membered DEL inside a living cell. We demonstrate a novel method using oocytes from the South African clawed frog Xenopus laevis. The large size of the oocytes of 1 µL, or 100 000 times bigger than a normal somatic cell, permits simple injection of DELs, thus resolving the fundamental problem of delivering DELs across cell membranes for in vivo screening. The target protein was expressed in the oocytes fused to a prey protein, to allow specific DNA labeling and hereby discriminate between DEL members binding to the target protein and the endogenous cell proteins. The 194 million member DEL was screened against three pharmaceutically relevant protein targets, p38α, ACSS2, and DOCK5. For all three targets multiple chemical clusters were identified. For p38α, validated hits with single digit nanomolar potencies were obtained. This work demonstrates a powerful new approach to DEL screening, which eliminates the need for highly purified active target protein and which performs the screening under physiological relevant conditions and thus is poised to increase the DEL amenable target space and reduce the attrition rates.

Structures of insect Imp-L2 suggest an alternative strategy for regulating the bioavailability of insulin-like hormones.

The insulin/insulin-like growth factor signalling axis is an evolutionary ancient and highly conserved hormonal system involved in the regulation of metabolism, growth and lifespan in animals. Human insulin is stored in the pancreas, while insulin-like growth factor-1 (IGF-1) is maintained in blood in complexes with IGF-binding proteins (IGFBP1-6). Insect insulin-like polypeptide binding proteins (IBPs) have been considered as IGFBP-like structural and functional homologues. Here, we report structures of the Drosophila IBP Imp-L2 in its free form and bound to Drosophila insulin-like peptide 5 and human IGF-1. Imp-L2 contains two immunoglobulin-like fold domains and its architecture is unrelated to human IGFBPs, suggesting a distinct strategy for bioavailability regulation of insulin-like hormones. Similar hormone binding modes may exist in other insect vectors, as the IBP sequences are highly conserved. Therefore, these findings may open research routes towards a rational interference of transmission of diseases such as malaria, dengue and yellow fevers.

Danish general practitioners' professional attention to children of parents with depression.

INTRODUCTION: Offspring of parents with depression has an increased risk of experiencing somatic and psychiatric diseases. Early child support can reduce this risk. This study aimed to describe general practitioners' (GPs) professional attention to children of depressed patients. METHODS: This was a survey study. We mailed ques-tion-naires to randomly selected Danish GPs. RESULTS: Among the 1,760 GPs invited, 890 (51%) partici-pated. Female GPs accounted for 45% of the respondents and 41% of the total GP population (p = 0.02). Respondents were younger than the mean GP population. A total of 94% of the GPs reported that giving attention to children of de-pressed parents was relevant, and 65% reported addressing the children's well-being during the consultation with the parent. A total of 39% of the GPs found that their knowledge about the significance of parental depression for the child was poor, and 41% were highly interested in learning more. Female GPs perceived that they had sufficient knowledge (66%) more frequently than male GPs (56%) (p < 0.001). GPs with sufficient perceived knowledge addressed the children's well-being more frequently than GPs with poor perceived knowledge (odds ratio = 5.8; 95% confidence interval: 4.14-8.07). CONCLUSIONS: This study showed a significant, under-utilised potential for improving GPs' awareness about children of parents with depression. Perceived knowledge of the potential impact of parental depression was crucial for the attention given to the children. FUNDING: The study was funded by The Central Denmark Region and the Danish National Research Foundation for Primary Care. TRIAL REGISTRATION: not relevant.

The Structure of a High-Affinity Kainate Receptor: GluK4 Ligand-Binding Domain Crystallized with Kainate.

Ionotropic glutamate receptors play a key role in fast neurotransmission in the CNS and have been linked to several neurological diseases and disorders. One subfamily is the kainate receptors, which are grouped into low-affinity (GluK1-3) and high-affinity (GluK4-5) receptors based on their affinity for kainate. Although structures of the ligand-binding domain (LBD) of all low-affinity kainate receptors have been reported, no structures of the high-affinity receptor subunits are available. Here, we present the X-ray structure of GluK4-LBD with kainate at 2.05 Å resolution, together with thermofluor and radiolabel binding affinity data. Whereas binding-site residues in GluK4 are most similar to the AMPA receptor subfamily, the domain closure and D1-D2 interlobe contacts induced by kainate are similar to the low-affinity kainate receptor GluK1. These observations provide a likely explanation for the high binding affinity of kainate at GluK4-LBD.

Structure and binding properties of a cameloid nanobody raised against KDM5B.

The histone demethylase KDM5B is considered to be a promising target for anticancer therapy. Single-chain antibodies from llama (nanobodies) have been raised to aid in crystallization and structure determination of this enzyme. The antigen-binding properties of 15 of these nanobodies have been characterized. The crystal structure of one of these (NB17) has been determined to a resolution of 1.85 Å. NB17 crystallizes in space group P4322 with six molecules in the asymmetric unit. The six molecules in the asymmetric unit pack as an entity with approximate D3 symmetry with interactions mediated by the CDR loops, which could act as a crystallization nucleus. NB17 does not bind to monomeric KDM5B residues 1-820, but is found to bind to aggregates formed after incubation at 310 K.

Crystal structure of the G3BP2 NTF2-like domain in complex with a canonical FGDF motif peptide.

The crystal structure of the NTF2-like domain of the human Ras GTPase SH3 Binding Protein (G3BP), isoform 2, was determined at a resolution of 2.75 Å in complex with a peptide containing a FGDF sequence motif. The overall structure of the protein is highly similar to the homodimeric N-terminal domains of the G3BP1 and Rasputin proteins. Recently, a subset of G3BP interacting proteins was recognized to share a common sequence motif, FGDF. The most studied binding partners, USP10 and viral nsP3, interfere with essential G3BP functions related to assembly of cellular stress granules. Reported molecular modeling suggested that FGDF-motif containing peptides bind in an extended conformation into a hydrophobic groove on the surface of the G3BP NTF2-like domain in a manner similar to the known binding of FxFG nucleoporin repeats. The results in this paper provide evidence for a different binding mode. The FGDF peptide binds and changes conformation of the protruding N-terminal residues by providing hydrophobic interactions to a symmetry related molecule that facilitated crystallization of the G3BP2 isoform.

Crystal structures of the human G3BP1 NTF2-like domain visualize FxFG Nup repeat specificity.

Ras GTPase Activating Protein SH3 Domain Binding Protein (G3BP) is a potential anti-cancer drug target implicated in several cellular functions. We have used protein crystallography to solve crystal structures of the human G3BP1 NTF2-like domain both alone and in complex with an FxFG Nup repeat peptide. Despite high structural similarity, the FxFG binding site is located between two alpha helices in the G3BP1 NTF2-like domain and not at the dimer interface as observed for nuclear transport factor 2. ITC studies showed specificity towards the FxFG motif but not FG and GLFG motifs. The unliganded form of the G3BP1 NTF2-like domain was solved in two crystal forms to resolutions of 1.6 and 3.3 Å in space groups P212121 and P6322 based on two different constructs, residues 1-139 and 11-139, respectively. Crystal packing of the N-terminal residues against a symmetry related molecule in the P212121 crystal form might indicate a novel ligand binding site that, however, remains to be validated. The crystal structures give insight into the nuclear transportation mechanisms of G3BP and provide a basis for future structure based drug design.

Crystal structure of the Rasputin NTF2-like domain from Drosophila melanogaster.

The crystal structure of the NTF2-like domain of the Drosophila homolog of Ras GTPase SH3 Binding Protein (G3BP), Rasputin, was determined at 2.7Å resolution. The overall structure is highly similar to nuclear transport factor 2: It is a homodimer comprised of a ß-sheet and three α-helices forming a cone-like shape. However, known binding sites for RanGDP and FxFG containing peptides show electrostatic and steric differences compared to nuclear transport factor 2. A HEPES molecule bound in the structure suggests a new, and possibly physiologically relevant, ligand binding site.

Structural model and trans-interaction of the entire ectodomain of the olfactory cell adhesion molecule.

The ectodomain of olfactory cell adhesion molecule (OCAM/NCAM2/RNCAM) consists of five immunoglobulin (Ig) domains (IgI-V), followed by two fibronectin-type 3 (Fn3) domains (Fn3I-II). A complete structural model of the entire ectodomain of human OCAM has been assembled from crystal structures of six recombinant proteins corresponding to different regions of the ectodomain. The model is the longest experimentally based composite structural model of an entire IgCAM ectodomain. It displays an essentially linear arrangement of IgI-V, followed by bends between IgV and Fn3I and between Fn3I and Fn3II. Proteins containing IgI-IgII domains formed stable homodimers in solution and in crystals. Dimerization could be disrupted in vitro by mutations in the dimer interface region. In conjunction with the bent ectodomain conformation, which can position IgI-V parallel with the cell surface, the IgI-IgII dimerization enables OCAM-mediated trans-interactions with an intercellular distance of about 20 nm, which is consistent with that observed in synapses.

Purification, crystallization and preliminary X-ray diffraction of the G3BP1 NTF2-like domain.

The nuclear transport factor 2-like (NTF2-like) domain of human G3BP1 was subcloned, overexpressed in Escherichia coli and purified. Crystals were obtained using the hanging-drop vapour-diffusion method. Diffraction data were collected to 3.6 Šresolution using synchrotron radiation. The crystals belonged to the hexagonal space group P6(3)22, with unit-cell parameters a=b=89.84, c=70.02 Å. The crystals contained one molecule per asymmetric unit, with an estimated solvent content of 56%. Initial phases were obtained by molecular replacement.

Bioinformatics and structural characterization of a hypothetical protein from Streptococcus mutans: implication of antibiotic resistance.

As an oral bacterial pathogen, Streptococcus mutans has been known as the aetiologic agent of human dental caries. Among a total of 1960 identified proteins within the genome of this organism, there are about 500 without any known functions. One of these proteins, SMU.440, has very few homologs in the current protein databases and it does not fall into any protein functional families. Phylogenetic studies showed that SMU.440 is related to a particular ecological niche and conserved specifically in some oral pathogens, due to lateral gene transfer. The co-occurrence of a MarR protein within the same operon among these oral pathogens suggests that SMU.440 may be associated with antibiotic resistance. The structure determination of SMU.440 revealed that it shares the same fold and a similar pocket as polyketide cyclases, which indicated that it is very likely to bind some polyketide-like molecules. From the interlinking structural and bioinformatics studies, we have concluded that SMU.440 could be involved in polyketide-like antibiotic resistance, providing a better understanding of this hypothetical protein. Besides, the combination of multiple methods in this study can be used as a general approach for functional studies of a protein with unknown function.

Structure of a fatty-acid-binding protein from Bacillus subtilis determined by sulfur-SAD phasing using in-house chromium radiation.

Sulfur single-wavelength anomalous dispersion (S-SAD) and halide-soaking methods are increasingly being used for ab initio phasing. With the introduction of in-house Cr X-ray sources, these methods benefit from the enhanced anomalous scattering of S and halide atoms, respectively. Here, these methods were combined to determine the crystal structure of BsDegV, a DegV protein-family member from Bacillus subtilis. The protein was cocrystallized with bromide and low-redundancy data were collected to 2.5 A resolution using Cr Kalpha radiation. 17 heavy-atom sites (ten sulfurs and seven bromides) were located using standard methods. The anomalous scattering of some of the BsDegV S atoms and Br atoms was weak, thus neither sulfurs nor bromides could be used alone for structure determination using the collected data. When all 17 heavy-atom sites were used for SAD phasing, an easily interpretable electron-density map was obtained after density modification. The model of BsDegV was built automatically and a palmitate was found tightly bound in the active site. Sequence alignment and comparisons with other known DegV structures provided further insight into the specificity of fatty-acid selection and recognition within this protein family.

Structure of the first PDZ domain of human PSD-93.

The crystal structure of the PDZ1 domain of human PSD-93 has been determined to 2.0 A resolution. The PDZ1 domain forms a crystallographic trimer that is also predicted to be stable in solution. The main contributions to the stabilization of the trimer seem to arise from interactions involving the PDZ1-PDZ2 linker region at the extreme C-terminus of PDZ1, implying that the oligomerization that is observed is not of biological significance in full-length PSD-93. Comparison of the structures of the binding cleft of PSD-93 PDZ1 with the previously reported structures of PSD-93 PDZ2 and PDZ3 as well as of the closely related human PSD-95 PDZ1 shows that they are very similar in terms of amino-acid composition. However, the cleft is significantly narrower in PSD-95. This could be part of the basis of peptide selectivity between PSD-93 PDZ1 and PSD-95 PDZ1.

Crystal structure of the Ig1 domain of the neural cell adhesion molecule NCAM2 displays domain swapping.

The crystal structure of the first immunoglobulin (Ig1) domain of neural cell adhesion molecule 2 (NCAM2/OCAM/RNCAM) is presented at a resolution of 2.7 A. NCAM2 is a member of the immunoglobulin superfamily of cell adhesion molecules (IgCAMs). In the structure, two Ig domains interact by domain swapping, as the two N-terminal beta-strands are interchanged. beta-Strand swapping at the terminal domain is the accepted mechanism of homophilic interactions amongst the cadherins, another class of CAMs, but it has not been observed within the IgCAM superfamily. Gel-filtration chromatography demonstrated the ability of NCAM2 Ig1 to form dimers in solution. Taken together, these observations suggest that beta-strand swapping could have a role in the molecular mechanism of homophilic binding for NCAM2.

Drug-induced pertubation of the aminothiol redox-status in patients with epilepsy: improvement by B-vitamins.

OBJECTIVES: Patients with epilepsy have excess morbidity and mortality due to ischemic cardiovascular disease. Many of these patients have elevated concentrations of plasma total homocysteine (Hcy), which is an acknowledged risk factor for cardiovascular disease, venous thromboembolic disease, foetal malformations and dementia. Hyperhomocysteinemia may have negative effects through mechanisms involving oxidative damage. In the present study, we have investigated the aminothiol redox-status in patients on antiepileptic drugs. Thereafter, in a subset of patients with elevated total Hcy, we evaluated the effect of B-vitamin therapy. METHODS: In the first part of the study, 101 patients on antiepileptic drugs were compared with 101 matched healthy controls. The redox-species of Hcy, cysteine and cysteinylglycine, the major aminothiols in plasma, were analyzed by high-performance liquid chromatography (HPLC). Hyperhomocysteinemia was defined as fasting total Hcy above 12 micromol/L and/or post-methionine load concentrations above 38 micromol/L. In the second part of the study, 33 patients identified with hyperhomocysteinemia were supplemented with three B-vitamins for 30 days; folic acid (B9), pyridoxine (B6) and riboflavin (B2). RESULTS: All redox-species of Hcy were significantly elevated in the patients, except the fasting concentrations of reduced Hcy (p=0.09). The reduced/total ratio of cysteine in fasting plasma was lower in the patients than in the controls: 5.20% vs. 6.19%, respectively (p=0.006). After 30 days of B-vitamin supplementation, the plasma concentrations of reduced, oxidized and protein-bound Hcy species were significantly lowered by 17%, 22% and 28%, respectively. The reduced/total ratio of cysteine rose from 4.9% to 7.9% (p=0.007). CONCLUSIONS: Patients on antiepileptic drugs have abnormal aminothiol redox-status associated with hyperhomocysteinemia. This is similar to findings in patients with cardiovascular disease. B-vitamin supplementation partially corrects the abnormal aminothiol redox-status. Possibly, B-vitamin supplementation may be useful in drug-induced hyperhomocysteinemia.

Structure of a SARS coronavirus-derived peptide bound to the human major histocompatibility complex class I molecule HLA-B*1501.

The human leukocyte antigen (HLA) class I system comprises a highly polymorphic set of molecules that specifically bind and present peptides to cytotoxic T cells. HLA-B*1501 is a prototypical member of the HLA-B62 supertype and only two peptide-HLA-B*1501 structures have been determined. Here, the crystal structure of HLA-B*1501 in complex with a SARS coronavirus-derived nonapeptide (VQQESSFVM) has been determined at high resolution (1.87 A). The peptide is deeply anchored in the B and F pockets, but with the Glu4 residue pointing away from the floor in the peptide-binding groove, making it available for interactions with a potential T-cell receptor.

Structure of the PPX/GPPA phosphatase from Aquifex aeolicus in complex with the alarmone ppGpp.

The crystal structure of the prototype exopolyphosphatase/guanosine pentaphosphate phosphohydrolase protein family member from Aquifex aeolicus in complex with the intracellular second messenger guanosine tetraphosphate was determined at 2.7-A resolution. The hydrolytic base is identified as E119. The dual specificity established for the Escherichia coli homolog is shown to be compatible with a common active site for guanosine pentaphosphate and polyphosphate hydrolysis. Distinct and different degrees of closure between the two domains of the enzyme are associated with substrate binding. The arginines R22 and R267, residing in different domains, are crucial for guanosine pentaphosphate specificity as they interact with the unique 3'-ribose phosphorylation.

Structure of rat acidic fibroblast growth factor at 1.4 A resolution.

Fibroblast growth factors (FGFs) constitute a family of 22 structurally related heparin-binding polypeptides that are involved in the regulation of cell growth, survival, differentiation and migration. Here, a 1.4 A resolution X-ray structure of rat FGF1 is presented. Two molecules are present in the asymmetric unit of the crystal and they coordinate a total of five sulfate ions. The structures of human, bovine and newt FGF1 have been published previously. Human and rat FGF1 are found to have very similar structures.

High resolution crystal structures of the p120 RasGAP SH3 domain.

X-ray structures of two crystal forms of the Src homology 3 domain (SH3) of the Ras GTPase activating protein (RasGAP) were determined at 1.5 and 1.8A resolution. The overall structure comprises a single domain with two tightly packed beta-sheets linked by a short helical segment. An important motif for peptide binding in other SH3 domains is not conserved in RasGAP. The RasGAP SH3 domain forms dimers in the crystal structures, which may provide new functional insight. The dimer interface involves residues also present in a peptide previously identified as an apoptotic sensitizer of tumor cells.