Solution structure of the cyclic-nucleotide binding homology domain of a KCNH channel

Identification of small-molecule binding sites of a ubiquitin-conjugating enzyme-UBE2T through fragment-based screening

UBE2T is an attractive target for drug development due to its linkage with several types of cancers. However, the druggability of ubiquitin-conjugating E2 (UBE2T) is low because of the lack of a deep and hydrophobic pocket capable of forming strong binding interactions with drug-like small molecules. Here, we performed fragment screening using 19 F-nuclear magnetic resonance (NMR) and validated the hits with 1 H-15 N-heteronuclear single quantum coherence (HSQC) experiment and X-ray crystallographic studies. The cocrystal structures obtained revealed the binding modes of the hit fragments and allowed for the characterization of the fragment-binding sites. Further screening of structural analogues resulted in the identification of a compound series with inhibitory effect on UBE2T activity. Our current study has identified two new binding pockets in UBE2T, which will be useful for the development of small molecules to regulate the function of this protein. In addition, the compounds identified in this study can serve as chemical starting points for the development of UBE2T modulators.

Identification and characterization of inhibitors covalently modifying catalytic cysteine of UBE2T and blocking ubiquitin transfer

UBE2T is an E2 ubiquitin ligase critical for ubiquitination of substrate and plays important roles in many diseases. Despite the important function, UBE2T is considered as an undruggable target due to lack of a pocket for binding to small molecules with satisfied properties for clinical applications. To develop potent and specific UBE2T inhibitors, we adopted a high-throughput screening assay and two compounds-ETC-6152 and ETC-9004 containing a sulfone tetrazole scaffold were identified. Solution NMR study demonstrated the direct interactions between UBE2T and compounds in solution. Further co-crystal structures reveal the binding modes of these compounds. Both compound hydrolysation and formation of a hydrogen bond with the thiol group of the catalytic cysteine were observed. The formation of covalent complex was confirmed with mass spectrometry. As these two compounds inhibit ubiquitin transfer, our study provides a strategy to develop potent inhibitors of UBE2T.

1 H, 15 N and 13 C resonance assignments of the Q61H mutant of human KRAS bound to GDP

KRAS proteins are small GTPases binding to the cell membrane and playing important roles in signal transduction. KRAS proteins form complexes with GTP and GDP to result in active and inactive conformations favouring interactions with different proteins. Mutations in KRAS have impact on the GTPase activity and some mutants are related to certain types of cancers. In addition to mutation at position 12, the Q61H mutant is also identified as an oncogenic mutant. Here, we describe resonance assignment for Q61H mutant of human KRAS-4B. A construct containing 1-169 residues of KRAS with a point mutation at position 61 (Q to H) was made for solution NMR studies. The backbone and some side chain resonance assignments were obtained using conventional multi-dimensional experiments. The secondary structures were analysed based on the assigned residues. As NMR is a powerful tool in probing target and ligand interactions, the assignment will be useful for later compound binding studies.

1H, 13C and 15N resonance assignments of the first BIR domain of cellular inhibitor of apoptosis protein 1

Cellular inhibitor of apoptosis protein-1 (cIAP-1) is member of inhibitor of apoptosis proteins (IAPs) which can affect apoptosis through interactions with caspases. cIAP-1 is a multi-domain protein and able to regulate apoptosis through interactions with proteins such as caspases and possesses E3 ligase activity. Human cIAP-1 contains three baculovirus IAP repeat (BIR) domains which are critical for protein-protein interactions. Here, we report NMR resonance assignments of the first BIR domain of human cIAP. Its secondary structures in solution were determined based on the assigned resonances. The dynamics of this domain was obtained, and our hydrogen-deuterium exchange experiment reveals that the first helix in BIR1 is exposed to the solvent. The availability of assignments of backbone and side chain resonances will be useful for probing protein-protein interactions.

Secondary Structures of the Transmembrane Domain of SARS-CoV-2 Spike Protein in Detergent Micelles

Spike protein of SARS-CoV-2 contains a single-span transmembrane (TM) domain and plays roles in receptor binding, viral attachment and viral entry to the host cells. The TM domain of spike protein is critical for viral infectivity. Herein, the TM domain of spike protein of SARS-CoV-2 was reconstituted in detergent micelles and subjected to structural analysis using solution NMR spectroscopy. The results demonstrate that the TM domain of the protein forms a helical structure in detergent micelles. An unstructured linker is identified between the TM helix and heptapeptide repeat 2 region. The linker is due to the proline residue at position 1213. Side chains of the three tryptophan residues preceding to and within the TM helix important for the function of S-protein might adopt multiple conformations which may be critical for their function. The side chain of W1212 was shown to be exposed to solvent and the side chains of residues W1214 and W1217 are buried in micelles. Relaxation study shows that the TM helix is rigid in solution while several residues have exchanges. The secondary structure and dynamics of the TM domain in this study provide insights into the function of the TM domain of spike protein.

Backbone resonance assignments for the SET domain of human methyltransferase NSD3 in complex with its cofactor

NSD3 is a histone H3 methyltransferase that plays an important role in chromatin biology. A construct containing the methyltransferase domain encompassing residues Q1049-K1299 of human NSD3 was obtained and biochemical activity was demonstrated using histone as a substrate. Here we report the backbone HN, N, Cα, C', and side chain Cβ assignments of the construct in complex with S-adenosyl-L-methionine (SAM). Based on these assignments, secondary structures of NSD3/SAM complex in solution were determined.

Structure of the Cyclic Nucleotide-Binding Homology Domain of the hERG Channel and Its Insight into Type 2 Long QT Syndrome

The human ether-à-go-go related gene (hERG) channel is crucial for the cardiac action potential by contributing to the fast delayed-rectifier potassium current. Mutations in the hERG channel result in type 2 long QT syndrome (LQT2). The hERG channel contains a cyclic nucleotide-binding homology domain (CNBHD) and this domain is required for the channel gating though molecular interactions with the eag domain. Here we present solution structure of the CNBHD of the hERG channel. The structural study reveals that the CNBHD adopts a similar fold to other KCNH channels. It is self-liganded and it contains a short β-strand that blocks the nucleotide-binding pocket in the β-roll. Folding of LQT2-related mutations in this domain was shown to be affected by point mutation. Mutations in this domain can cause protein aggregation in E. coli cells or induce conformational changes. One mutant-R752W showed obvious chemical shift perturbation compared with the wild-type, but it still binds to the eag domain. The helix region from the N-terminal cap domain of the hERG channel showed unspecific interactions with the CNBHD.

NMR structural characterization of the N-terminal active domain of the gyrase B subunit from Pseudomonas aeruginosa and its complex with an inhibitor

The N-terminal ATP binding domain of the DNA gyrase B subunit is a validated drug target for antibacterial drug discovery. Structural information for this domain (pGyrB) from Pseudomonas aeruginosa is still missing. In this study, the interaction between pGyrB and a bis-pyridylurea inhibitor was characterized using several biophysical methods. We further carried out structural analysis of pGyrB using NMR spectroscopy. The secondary structures of free and inhibitor bound pGyrB were obtained based on backbone chemical shift assignment. Chemical shift perturbation and NOE experiments demonstrated that the inhibitor binds to the ATP binding pocket. The results of this study will be helpful for drug development targeting P. aeruginosa.

Getting to the heart of hERG K(+) channel gating

Potassium ion channels encoded by the human ether-a-go-go related gene (hERG) form the ion-conducting subunit of the rapid delayed rectifier potassium current (IKr ). Although hERG channels exhibit a widespread tissue distribution they play a particularly important role in the heart. There has been considerable interest in hERG K(+) channels for three main reasons. First, they have very unusual gating kinetics, most notably rapid and voltage-dependent inactivation coupled to slow deactivation, which has led to the suggestion that they may play a specific role in the suppression of arrhythmias. Second, mutations in hERG are the cause of 30-40% of cases of congenital long QT syndrome (LQTS), the commonest inherited primary arrhythmia syndrome. Third, hERG is the molecular target for the vast majority of drugs that cause drug-induced LQTS, the commonest cause of drug-induced arrhythmias and cardiac death. Drug-induced LQTS has now been reported for a large range of both cardiac and non-cardiac drugs, in which this side effect is entirely undesired. In recent years there have been comprehensive reviews published on hERG K(+) channels (Vandenberg et al. 2012) and we will not re-cover this ground. Rather, we focus on more recent work on the structural basis and dynamics of hERG gating with an emphasis on how the latest developments may facilitate translational research in the area of stratifying risk of arrhythmias.

Insight into the molecular interaction between the cyclic nucleotide-binding homology domain and the eag domain of the hERG channel

The gating of the hERG channel is regulated by its eag domain through molecular interaction with either the cyclic nucleotide-binding homology domain (CNBHD) or the linker between transmembrane segments 4 and 5. Our NMR study on the purified CNBHD demonstrated that it contains nine β-strands and does not bind cAMP. We show that the eag domain binds to the CBND through an interface containing several disease-associated mutations. The N-terminal cap domain and R56 in the eag domain are important for the interaction with the CNBHD. Residues from the CNBHD that were affected by the interaction with the eag domain were also identified. A R56Q mutation does not cause major structural changes in the eag domain and showed reduced interaction with the CNBHD.