IceBear: an intuitive and versatile web application for research-data tracking from crystallization experiment to PDB deposition

HEIDI: an experiment-management platform enabling high-throughput fragment and compound screening

The Swiss Light Source facilitates fragment-based drug-discovery campaigns for academic and industrial users through the Fast Fragment and Compound Screening (FFCS) software suite. This framework is further enriched by the option to utilize the Smart Digital User (SDU) software for automated data collection across the PXI, PXII and PXIII beamlines. In this work, the newly developed HEIDI webpage (https://heidi.psi.ch) is introduced: a platform crafted using state-of-the-art software architecture and web technologies for sample management of rotational data experiments. The HEIDI webpage features a data-review tab for enhanced result visualization and provides programmatic access through a representational state transfer application programming interface (REST API). The migration of the local FFCS MongoDB instance to the cloud is highlighted and detailed. This transition ensures secure, encrypted and consistently accessible data through a robust and reliable REST API tailored for the FFCS software suite. Collectively, these advancements not only significantly elevate the user experience, but also pave the way for future expansions and improvements in the capabilities of the system.

Discovery of 2-Amide-3-methylester Thiophenes that Target SARS-CoV-2 Mac1 and Repress Coronavirus Replication, Validating Mac1 as an Antiviral Target

The COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus has made it clear that further development of antiviral therapies will be needed. Here, we describe small-molecule inhibitors for SARS-CoV-2 Mac1, which counters ADP-ribosylation-mediated innate immune responses. Three high-throughput screening hits had the same 2-amide-3-methylester thiophene scaffold. We studied the compound binding mode using X-ray crystallography, allowing us to design analogues. Compound 27 (MDOLL-0229) had an IC50 of 2.1 μM and was selective for CoV Mac1 proteins after profiling for activity against a panel of viral and human proteins. The improved potency allowed testing of its effect on virus replication, and indeed, 27 inhibited replication of both murine hepatitis virus (MHV) prototypes CoV and SARS-CoV-2. Sequencing of a drug-resistant MHV identified mutations in Mac1, further demonstrating the specificity of 27. Compound 27 is the first Mac1-targeted small molecule demonstrated to inhibit coronavirus replication in a cell model.

Structural enzymology studies with the substrate 3S-hydroxybutanoyl-CoA: bifunctional MFE1 is a less efficient dehydrogenase than monofunctional HAD

Multifunctional enzyme, type-1 (MFE1) catalyzes the second and third step of the β-oxidation cycle, being, respectively, the 2E-enoyl-CoA hydratase (ECH) reaction (N-terminal part, crotonase fold) and the NAD+-dependent, 3S-hydroxyacyl-CoA dehydrogenase (HAD) reaction (C-terminal part, HAD fold). Structural enzymological properties of rat MFE1 (RnMFE1) as well as of two of its variants, namely the E123A variant (a glutamate of the ECH active site is mutated into alanine) and the BCDE variant (without domain A of the ECH part), were studied, using as substrate 3S-hydroxybutanoyl-CoA. Protein crystallographic binding studies show the hydrogen bond interactions of 3S-hydroxybutanoyl-CoA as well as of its 3-keto, oxidized form, acetoacetyl-CoA, with the catalytic glutamates in the ECH active site. Pre-steady state binding experiments with NAD+ and NADH show that the kon and koff rate constants of the HAD active site of monomeric RnMFE1 and the homologous human, dimeric 3S-hydroxyacyl-CoA dehydrogenase (HsHAD) for NAD+ and NADH are very similar, being the same as those observed for the E123A and BCDE variants. However, steady state and pre-steady state kinetic data concerning the HAD-catalyzed dehydrogenation reaction of the substrate 3S-hydroxybutanoyl-CoA show that, respectively, the kcat and kchem rate constants for conversion into acetoacetyl-CoA by RnMFE1 (and its two variants) are about 10 fold lower as when catalyzed by HsHAD. The dynamical properties of dehydrogenases are known to be important for their catalytic efficiency, and it is discussed that the greater complexity of the RnMFE1 fold correlates with the observation that RnMFE1 is a slower dehydrogenase than HsHAD.

Discovery of 2-amide-3-methylester thiophenes that target SARS-CoV-2 Mac1 and repress coronavirus replication, validating Mac1 as an anti-viral target

The COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus has made it clear that further development of antiviral therapies will be needed to combat additional SARS-CoV-2 variants or novel CoVs. Here, we describe small molecule inhibitors for SARS-CoV-2 Mac1, which counters ADP-ribosylation mediated innate immune responses. The compounds inhibiting Mac1 were discovered through high-throughput screening (HTS) using a protein FRET-based competition assay and the best hit compound had an IC50 of 14 μM. Three validated HTS hits have the same 2-amide-3-methylester thiophene scaffold and the scaffold was selected for structure-activity relationship (SAR) studies through commercial and synthesized analogs. We studied the compound binding mode in detail using X-ray crystallography and this allowed us to focus on specific features of the compound and design analogs. Compound 27 (MDOLL-0229) had an IC50 of 2.1 μM and was generally selective for CoV Mac1 proteins after profiling for activity against a panel of viral and human ADP-ribose binding proteins. The improved potency allowed testing of its effect on virus replication and indeed, 27 inhibited replication of both MHVa prototype CoV, and SARS-CoV-2. Furthermore, sequencing of a drug-resistant MHV identified mutations in Mac1, further demonstrating the specificity of 27. Compound 27 is the first Mac1 targeted small molecule demonstrated to inhibit coronavirus replication in a cell model. This, together with its well-defined binding mode, makes 27 a good candidate for further hit/lead-optimization efforts.

Structural basis for different membrane-binding properties of E. coli anaerobic and human mitochondrial β-oxidation trifunctional enzymes

Facultative anaerobic bacteria such as Escherichia coli have two α2β2 heterotetrameric trifunctional enzymes (TFE), catalyzing the last three steps of the β-oxidation cycle: soluble aerobic TFE (EcTFE) and membrane-associated anaerobic TFE (anEcTFE), closely related to the human mitochondrial TFE (HsTFE). The cryo-EM structure of anEcTFE and crystal structures of anEcTFE-α show that the overall assembly of anEcTFE and HsTFE is similar. However, their membrane-binding properties differ considerably. The shorter A5-H7 and H8 regions of anEcTFE-α result in weaker α-β as well as α-membrane interactions, respectively. The protruding H-H region of anEcTFE-β is therefore more critical for membrane-association. Mutational studies also show that this region is important for the stability of the anEcTFE-β dimer and anEcTFE heterotetramer. The fatty acyl tail binding tunnel of the anEcTFE-α hydratase domain, as in HsTFE-α, is wider than in EcTFE-α, accommodating longer fatty acyl tails, in good agreement with their respective substrate specificities.

An engineered variant of MECR reductase reveals indispensability of long-chain acyl-ACPs for mitochondrial respiration

Mitochondrial fatty acid synthesis (mtFAS) is essential for respiratory function. MtFAS generates the octanoic acid precursor for lipoic acid synthesis, but the role of longer fatty acid products has remained unclear. The structurally well-characterized component of mtFAS, human 2E-enoyl-ACP reductase (MECR) rescues respiratory growth and lipoylation defects of a Saccharomyces cerevisiae Δetr1 strain lacking native mtFAS enoyl reductase. To address the role of longer products of mtFAS, we employed in silico molecular simulations to design a MECR variant with a shortened substrate binding cavity. Our in vitro and in vivo analyses indicate that the MECR G165Q variant allows synthesis of octanoyl groups but not long chain fatty acids, confirming the validity of our computational approach to engineer substrate length specificity. Furthermore, our data imply that restoring lipoylation in mtFAS deficient yeast strains is not sufficient to support respiration and that long chain acyl-ACPs generated by mtFAS are required for mitochondrial function.

[1,2,4]Triazolo[3,4-b]benzothiazole Scaffold as Versatile Nicotinamide Mimic Allowing Nanomolar Inhibition of Different PARP Enzymes

We report [1,2,4]triazolo[3,4-b]benzothiazole (TBT) as a new inhibitor scaffold, which competes with nicotinamide in the binding pocket of human poly- and mono-ADP-ribosylating enzymes. The binding mode was studied through analogues and cocrystal structures with TNKS2, PARP2, PARP14, and PARP15. Based on the substitution pattern, we were able to identify 3-amino derivatives 21 (OUL243) and 27 (OUL232) as inhibitors of mono-ARTs PARP7, PARP10, PARP11, PARP12, PARP14, and PARP15 at nM potencies, with 27 being the most potent PARP10 inhibitor described to date (IC₅₀ of 7.8 nM) and the first PARP12 inhibitor ever reported. On the contrary, hydroxy derivative 16 (OUL245) inhibits poly-ARTs with a selectivity toward PARP2. The scaffold does not possess inherent cell toxicity, and the inhibitors can enter cells and engage with the target protein. This, together with favorable ADME properties, demonstrates the potential of TBT scaffold for future drug development efforts toward selective inhibitors against specific enzymes.

Crystal structure of the collagen prolyl 4-hydroxylase (C-P4H) catalytic domain complexed with PDI: Toward a model of the C-P4H α(2)β(2) tetramer

Collagen prolyl 4-hydroxylases (C-P4H) are α₂β₂ tetramers, which catalyze the prolyl 4-hydroxylation of procollagen, allowing for the formation of the stable triple-helical collagen structure in the endoplasmic reticulum. The C-P4H α-subunit provides the N-terminal dimerization domain, the middle peptide-substrate-binding (PSB) domain, and the C-terminal catalytic (CAT) domain, whereas the β-subunit is identical to the enzyme protein disulfide isomerase (PDI). The structure of the N-terminal part of the α-subunit (N-terminal region and PSB domain) is known, but the structures of the PSB-CAT linker region and the CAT domain as well as its mode of assembly with the β/PDI subunit, are unknown. Here, we report the crystal structure of the CAT domain of human C-P4H-II complexed with the intact β/PDI subunit, at 3.8 Å resolution. The CAT domain interacts with the a, b', and a' domains of the β/PDI subunit, such that the CAT active site is facing bulk solvent. The structure also shows that the C-P4H-II CAT domain has a unique N-terminal extension, consisting of α-helices and a β-strand, which is the edge strand of its major antiparallel β-sheet. This extra region of the CAT domain interacts tightly with the β/PDI subunit, showing that the CAT-PDI interface includes an intersubunit disulfide bridge with the a' domain and tight hydrophobic interactions with the b' domain. Using this new information, the structure of the mature C-P4H-II α₂β₂ tetramer is predicted. The model suggests that the CAT active-site properties are modulated by α-helices of the N-terminal dimerization domains of both subunits of the α₂-dimer.

Analogs of TIQ-A as inhibitors of human mono-ADP-ribosylating PARPs

The scaffold of TIQ-A, a previously known inhibitor of human poly-ADP-ribosyltransferase PARP1, was utilized to develop inhibitors against human mono-ADP-ribosyltransferases through structure-guided design and activity profiling. By supplementing the TIQ-A scaffold with small structural changes, based on a PARP10 inhibitor OUL35, selectivity changed from poly-ADP-ribosyltransferases towards mono-ADP-ribosyltransferases. Binding modes of analogs were experimentally verified by determining complex crystal structures with mono-ADP-ribosyltransferase PARP15 and with poly-ADP-ribosyltransferase TNKS2. The best analogs of the study achieved 10-20-fold selectivity towards mono-ADP-ribosyltransferases PARP10 and PARP15 while maintaining micromolar potencies. The work demonstrates a route to differentiate compound selectivity between mono- and poly-ribosyltransferases of the human ARTD family.

Substrate specificity and conformational flexibility properties of the Mycobacterium tuberculosis β-oxidation trifunctional enzyme

The Mycobacterium tuberculosis trifunctional enzyme (MtTFE) is an α₂β₂ tetrameric enzyme. The α -chain harbors the 2E-enoyl-CoA hydratase (ECH) and 3S-hydroxyacyl-CoA dehydrogenase (HAD) activities and the β -chain provides the 3-ketoacyl-CoA thiolase (KAT) activity. Enzyme kinetic data reported here show that medium and long chain enoyl-CoA molecules are preferred substrates for MtTFE. Modelling studies indicate how the linear medium and long chain acyl chains of these substrates can bind to each of the active sites. In addition, crystallographic binding studies have identified three new CoA binding sites which are different from the previously known CoA binding sites of the three TFE active sites. Structure comparisons provide new insights into the properties of ECH, HAD and KAT active sites of MtTFE. The interactions of the adenine moiety of CoA with loop-2 of the ECH active site cause a conformational change of this loop by which a competent ECH active site is formed. The NAD⁺ binding domain (domain C) of the HAD part of MtTFE has only a few interactions with the rest of the complex and adopts a range of open conformations, whereas the A-domain of the ECH part is rigidly fixed with respect to the HAD part. Two loops, the CB1-CA1 region and the catalytic CB4-CB5 loop, near the thiolase active site and the thiolase dimer interface, have high B-factors. Structure comparisons suggest that a competent and stable thiolase dimer is formed only when complexed with the α -chains, highlighting the importance of the assembly for the proper functioning of the complex.

Crystallographic binding studies of rat peroxisomal multifunctional enzyme type 1 with 3-ketodecanoyl-CoA: capturing active and inactive states of its hydratase and dehydrogenase catalytic sites

The peroxisomal multifunctional enzyme type 1 (MFE1) catalyzes two successive reactions in the β-oxidation cycle: the 2E-enoyl-CoA hydratase (ECH) and NAD+-dependent 3S-hydroxyacyl-CoA dehydrogenase (HAD) reactions. MFE1 is a monomeric enzyme that has five domains. The N-terminal part (domains A and B) adopts the crotonase fold and the C-terminal part (domains C, D and E) adopts the HAD fold. A new crystal form of MFE1 has captured a conformation in which both active sites are noncompetent. This structure, at 1.7 Å resolution, shows the importance of the interactions between Phe272 in domain B (the linker helix; helix H10 of the crotonase fold) and the beginning of loop 2 (of the crotonase fold) in stabilizing the competent ECH active-site geometry. In addition, protein crystallographic binding studies using optimized crystal-treatment protocols have captured a structure with both the 3-ketodecanoyl-CoA product and NAD+bound in the HAD active site, showing the interactions between 3-ketodecanoyl-CoA and residues of the C, D and E domains. Structural comparisons show the importance of domain movements, in particular of the C domain with respect to the D/E domains and of the A domain with respect to the HAD part. These comparisons suggest that the N-terminal part of the linker helix, which interacts tightly with domains A and E, functions as a hinge region for movement of the A domain with respect to the HAD part.