MJK2, a K+Channel from M. Jannaschii Mediates pH Dependent Potassium Transport Activity

MjK2 was expressed in E. coli cells as a fusion protein containing N-or C-terminal an antibody binding site and a histidinehexamer. The C-terminal tagged fusion protein allows the expression and purification of an extra soluble RCK domain at p34 kDa, whereas this additional RCK domain was lost when the N-terminal tagged construct was used. Upon removal of the fusion peptide from the purified N-terminal tagged channel monomer, MjK2 occurred as a stable tetramer when incubated with synthetic lipid. The channel activity was studied after reconstitution into liposomes by single channel recording or by an optical assay with the potassium sensing dye, PBFI. First the channel function was improved by single channel recording. Single channel recording confirmed the pH dependence of the channel activity with single channel conductances of 42, 70, 85 and 202 pS and indicated that a functional K+ channel was formed. To study the function of the reconstituted MjK2 activity in an optical assay the potassium release was initiated when the external BaCl2 block was compensated by addition of EDTA. The release of potassium was mediated by reconstituted MjK2 at low pH or by the presence of internal calcium at high pH. MgCl2 had no or weak effect, whereas cAMP at low pH caused a complete loss of potassium during the preparation. Alignments studies revealed that MjK2 has different structural features in the channel pore and the RCK composition and therefore a different function can be expected. Amino acid sequence and structural alignments showed that a Ca2+ binding site and a typical nucleotide-binding site is not present in the RCK domain of MjK2 and therefore a different behavior could be expected. In addition a lysine reach linker region as found in human sperm K+ channels hslo1 and hslo3can play similar role in the gating behavior.Leibniz University Hannover/WiF programDF

Triiodothyronine Acts as a Smart Influencer on Hsp90 via a Triiodothyronine Binding Site

Microarray-based experiments revealed that thyroid hormone triiodothyronine (T3) enhanced the binding of Cy5-labeled ATP on heat shock protein 90 (Hsp90). By molecular docking experiments with T3 on Hsp90, we identified a T3 binding site (TBS) near the ATP binding site on Hsp90. A synthetic peptide encoding HHHHHHRIKEIVKKHSQFIGYPITLFVEKE derived from the TBS on Hsp90 showed, in MST experiments, the binding of T3 at an EC50 of 50 μM. The binding motif can influence the activity of Hsp90 by hindering ATP accessibility or the release of ADP

Microarray-based screening system identifies temperature-controlled activity of Connexin 26 that is distorted by mutations

Here, we show that human Connexin 26 (hCx26 or Cx26WT) hemichannel opening rapidly enables the transport of small molecules when triggered by temperature and by compensation of the Ca2+ blockade with EDTA. Point mutations within Cx26 were analysed by a novel optical microarray-based Lucifer Yellow uptake assay or by two electrode voltage clamp (TEVC) on frog oocytes to monitor simultaneous activities of channel proteins. Point mutations L90P, F161S, R184P or K188N influenced the temperature-dependent activity drastically. Since several mutations blocked trafficking, the temperature-dependent activity of the recombinant synthesized and purified wild-type Cx26WT and Cx26K188N hemichannel was tested by liposome flux assay (LFA) and on a microarray-based Lucifer Yellow uptake assay under warm conditions (>30 °C). The data from TEVC measurements and dye flux experiments showed that the mutations gave no or only a weak activity at increased temperature (>30 °C). We conclude that the position K188 in the Cx26WT forms a temperature-sensitive salt bridge with E47 whereas the exchange to K188N destabilizes the network loop- gating filter, which was recently identified as a part of the flexible Ca2+ binding site. We assume that the temperature sensitivity of Cx26 is required to protect cells from uncontrolled release or uptake activities through Cx26 hemichannels

Fluorescence Masking Based Multifunctional Quantum Dots’ Assay for HSP90α Interactions Detection

HSP90α is one of the most common stress proteins in cells; hence, it is a good target for developing drugs and testing systems for cancer or physical stress levels in humans. Streptavidin conjugated quantum dots (Sav-QDs) are widely used as fluorophores for biosensing to overcome chemical labelling problems. In this work, we have attempted to develop a multifunctional and robust assay for HSP90α. The detection technique was based on the masking of the fluorescence of spotted Sav-QDs on nitrocellulose chips (NC). Biotinylated ligand/antibody attaches to the spotted Sav-QD and then HSP90α is attached, which causes the masking of fluorescence. The masking of fluorescence was used to detect protein–ligand interactions, the effect of inhibitors, protein–protein interactions, and the presence of protein in the biological sample. The load of detection (LoD) of the assay lies in the nano molar range, making it a sensitive assay. The results from the experiments suggest that the used approach is promising for developing a multifunctional, robust, and sensitive assay for proteins that can be used for point-of-care detection in complex biological samples

Analysis of SARS-CoV-2 spike RBD binding to ACE2 and its inhibition by fungal cohaerin C using surface enhanced Raman spectroscopy

The structure of the SARS-CoV-2 spike RBD and human ACE2 as well as changes in the structure due to binding activities were analysed using surface enhanced Raman spectroscopy. The inhibitor cohaerin C was applied to inhibit the binding between spike RBD and ACE2. Differences and changes in the Raman spectra were determined using deconvolution of the amide bands and principal component analysis. We thus demonstrate a fast and label-free analysis of the protein structures and the differentiation between bound and unbound states. The approach is suitable for sensing and screening and might be relevant to investigate other protein systems as well

Multiplexed heat shock protein microarray as a screening platform for the selection of novel drug compounds

In diseases such as cancer, Alzheimer’s disease or malaria, disease-related proteins take advantage of the heat shock protein (HSP) control system for their own activation or maturation. There is a quest to find inhibitors that specifically bind to the HSPs. Here, we report on a novel multiplexed assay system for inhibitor screening based on a protein microarray (MA) technique that was developed for routine applications with storable MAs. Purified HSPs are printed as full-length proteins on microarrays and used as a drug target for the screening of new inhibitors. Derivatives obtained by a combination of biological and chemical synthesis were tested as competitors of ATP with a suggested affinity for several HSP proteins which are hHSP from human, AtHSP83 (Arabidopsis thaliana) and HtpG from Helicobacter pylori. Some of these new derivatives exerted selectivity between human and bacterial heat shock proteins. Printed human HSP90 was used to test the binding of denatured proteins on the client binding site of human HSP90, since the full-length HSP maintains the capability to bind putative clients or cochaperones. Initial data revealed that the microarray application can be used to identify directly elevated heat-shock protein levels in cancer cell lysates. We suggest that microarray-based assaying of HSP levels can be used as a marker for determining stress levels.DFG/Ki 13-

Multiformin-Type Azaphilones Prevent SARS-CoV-2 Binding to ACE2 Receptor

Protein microarray screenings identified fungal natural products from the azaphilone family as potent inhibitors of SARS-CoV-2 spike protein binding to host ACE2 receptors. Cohaerin F, as the most potent substance from the cohaerin group, led to more than 50% less binding of ACE2 and SARS-CoV-2 spike protein. A survey for structurally related azaphilones yielded the structure elucidation of six new multiformins E–J (10–15) and the revision of the stereochemistry of the multiformins. Cohaerin and multiformin azaphilones (1–5, 8, 12) were assessed for their activity in a cell-based infection assay. Calu-3 cells expressing human ACE2 receptor showed more than 75% and 50% less infection by SARS-CoV-2 pseudotyped lentivirus particles after treatment with cohaerin C (1) and cohaerin F (4), respectively. Multiformin C (8) and G (12) that nearly abolished the infection of cells. Our data show that multiformin-type azaphilones prevent the binding of SARS-CoV-2 to the cell entry receptor ACE2

A Chemical Chaperone Restores Connexin 26 Mutant Activity

Mutations in connexin 26 (Cx26) cause hearing disorders of a varying degree. Herein, to identify compounds capable of restoring the function of mutated Cx26, a novel miniaturized microarray-based screening system was developed to perform an optical assay of Cx26 functionality. These molecules were identified through a viability assay using HeLa cells expressing wild-type (WT) Cx26, which exhibited sensitivity toward the HSP90 inhibitor radicicol in the submicromolar concentration range. Open Cx26 hemichannels are assumed to mediate the passage of molecules up to 1000 Da in size. Thus, by releasing radicicol, WT Cx26 active hemichannels in HeLa cells contribute to a higher survival rate and lower cell viability when Cx26 is mutated. HeLa cells expressing Cx26 mutations exhibited reduced viability in the presence of radicicol, such as the mutants F161S or R184P. Next, molecules exhibiting chemical chaperoning activity, suspected of restoring channel function, were assessed regarding whether they induced superior sensitivity toward radicicol and increased HeLa cell viability. Through a viability assay and microarray-based flux assay that uses Lucifer yellow in HeLa cells, compounds 3 and 8 were identified to restore mutant functionality. Furthermore, thermophoresis experiments revealed that only 3 (VRT-534) exhibited dose-responsive binding to recombinant WT Cx26 and mutant Cx26K188N with half maximal effective concentration values of 19 and ∼5 μM, respectively. The findings of this study reveal that repurposing compounds already being used to treat other diseases, such as cystic fibrosis, in combination with functional bioassays and binding tests can help identify novel potential candidates that can be used to treat hearing disorders

Is Simultaneous Binding to DNA and Gyrase Important for the Antibacterial Activity of Cystobactamids?

Cystobactamids are aromatic oligoamides that exert their natural antibacterial properties by inhibition of bacterial gyrases. Such aromatic oligoamides were proposed to inhibit α-helix-mediated protein-protein interactions and may serve for specific recognition of DNA. Based on this suggestion, we designed new derivatives that have duplicated cystobactamid triarene units as model systems to decipher the specific binding mode of cystobactamids to double stranded DNA. Solution NMR analyses revealed that natural cystobactamids as well as their elongated analogues show an overall bent shape at their central aliphatic unit, with an average CX-CY-CZ angle of ~110 degrees. Our finding is corroborated by the target-bound structure of close analogues, as established by cryo-EM very recently. Cystobactamid CN-861-2 binds directly to the bacterial gyrase with an affinity of 9 μM, and also exhibits DNA-binding properties with specificity for AT-rich DNA. Elongation/dimerization of the triarene subunit of native cystobactamids is demonstrated to lead to an increase in DNA binding affinity. This implies that cystobactamids’ gyrase inhibitory activity necessitates not just interaction with the gyrase itself, but also with DNA via their triarene unit

Identification of a Thyroid Hormone Binding Site in Hsp90 with Implications for Its Interaction with Thyroid Hormone Receptor Beta

While many proteins are known clients of heat shock protein 90 (Hsp90), it is unclear whether the transcription factor, thyroid hormone receptor beta (TRb), interacts with Hsp90 to control hormonal perception and signaling. Higher Hsp90 expression in mouse fibroblasts was elicited by the addition of triiodothyronine (T3). T3 bound to Hsp90 and enhanced adenosine triphosphate (ATP) binding of Hsp90 due to a specific binding site for T3, as identified by molecular docking experiments. The binding of TRb to Hsp90 was prevented by T3 or by the thyroid mimetic sobetirome. Purified recombinant TRb trapped Hsp90 from cell lysate or purified Hsp90 in pull-down experiments. The affinity of Hsp90 for TRb was 124 nM. Furthermore, T3 induced the release of bound TRb from Hsp90, which was shown by streptavidin-conjugated quantum dot (SAv-QD) masking assay. The data indicate that the T3 interaction with TRb and Hsp90 may be an amplifier of the cellular stress response by blocking Hsp90 activity