First Evidence of Acyl-Hydrolase/Lipase Activity From Human Probiotic Bacteria: Lactobacillus rhamnosus GG and Bifidobacterium longum NCC 2705

Lactobacillus rhamnosus GG (ATCC 53103) and Bifidobacterium longum NCC 2705 are among the most studied probiotics. However, the first evidence of acyl hydrolase/lipase of two annotated proteins, one in each genome of these strains, is reported in this work. Signal peptide analysis has predicted that these proteins are exported to the extracellular medium. Both proteins were produced in Escherichia coli, purified and characterized. Molecular masses (without signal peptides) were 27 and 52.3 kDa for the proteins of L. rhamnosus and B. longum, respectively. Asymmetrical flow field-flow fractionation analysis has shown that both proteins are present as monomers in their native forms at pH 7. Both have shown enzymatic activity on pNP-laurate at pH 7 and 37°C. The enzyme from L. rhamnosus was characterized deeper, showing preference on pNP-esters with short chain fatty acids. In addition, a computational model of the 3D structure has allowed the prediction of the catalytic amino acids. The enzymatic activities using synthetic substrates were very low for both enzymes. The investigation of natural substrates and biological functions of these enzymes is still open.

Cancer-Associated Substitutions in RNA Recognition Motifs of PUF60 and U2AF65 Reveal Residues Required for Correct Folding and 3' Splice-Site Selection

U2AF65 (U2AF2) and PUF60 (PUF60) are splicing factors important for recruitment of the U2 small nuclear ribonucleoprotein to lariat branch points and selection of 3′ splice sites (3′ss). Both proteins preferentially bind uridine-rich sequences upstream of 3′ss via their RNA recognition motifs (RRMs). Here, we examined 36 RRM substitutions reported in cancer patients to identify variants that alter 3′ss selection, RNA binding and protein properties. Employing PUF60- and U2AF65-dependent 3′ss previously identified by RNA-seq of depleted cells, we found that 43% (10/23) and 15% (2/13) of independent RRM mutations in U2AF65 and PUF60, respectively, conferred splicing defects. At least three RRM mutations increased skipping of internal U2AF2 (~9%, 2/23) or PUF60 (~8%, 1/13) exons, indicating that cancer-associated RRM mutations can have both cis- and trans-acting effects on splicing. We also report residues required for correct folding/stability of each protein and map functional RRM substitutions on to existing high-resolution structures of U2AF65 and PUF60. These results identify new RRM residues critical for 3′ss selection and provide relatively simple tools to detect clonal RRM mutations that enhance the mRNA isoform diversity.

Structural and biophysical properties of RIG-I bound to dsRNA with G-U wobble base pairs

Retinoic acid-inducible gene I (RIG-I) is responsible for innate immunity via the recognition of short double-stranded RNAs in the cytosol. With the clue that G-U wobble base pairs in the influenza A virus's RNA promoter region are responsible for RIG-I activation, we determined the complex structure of RIG-I ΔCARD and a short hairpin RNA with G-U wobble base pairs by X-ray crystallography. Interestingly, the overall helical backbone trace was not affected by the presence of the wobble base pairs; however, the base pair inclination and helical axis angle changed upon RIG-I binding. NMR spectroscopy revealed that RIG-I binding renders the flexible base pair of the influenza A virus's RNA promoter region between the two G-U wobble base pairs even more flexible. Binding to RNA with wobble base pairs resulted in a more flexible RIG-I complex. This flexible complex formation correlates with the entropy-favoured binding of RIG-I and RNA, which results in tighter binding affinity and RIG-I activation. This study suggests that the structure and dynamics of RIG-I are tailored to the binding of specific RNA sequences with different flexibility.

Thermodynamic contribution of iodine atom to the binding of heterogeneously polyhalogenated benzotriazoles by the catalytic subunit of human protein kinase CK2

A series of novel benzotriazole derivatives containing iodine atom(s) were synthesized. The binding of these compounds to the catalytic subunit of human protein kinase CK2 was evaluated using differential scanning fluorimetry. The obtained thermodynamic data were compared with those determined previously for the brominated and chlorinated benzotriazole analogues to get a deeper insight into the thermodynamic contribution of iodine substitution to the free energy of ligand binding. We have shown that iodine atom(s) attached to the benzene ring of benzotriazole enhance(s) its binding by the target protein. This effect is the strongest when two iodine atoms are attached at positions peripheral to the triazole ring, which according to the structures deposited in protein data bank may be indicative for the formation of the halogen bond between iodine and carbonyl groups of residues located in the hinge region of the protein. Finally, quantitative structure-activity relationship analysis pointed the solute hydrophobicity as the main factor contributing to the binding affinity.

Targeting of Fumarate Hydratase from Mycobacterium tuberculosis Using Allosteric Inhibitors with a Dimeric-Binding Mode

With the growing worldwide prevalence of antibiotic-resistant strains of tuberculosis (TB), new targets are urgently required for the development of treatments with novel modes of action. Fumarate hydratase (fumarase), a vulnerable component of the citric acid cycle in Mycobacterium tuberculosis (Mtb), is a metabolic target that could satisfy this unmet demand. A key challenge in the targeting of Mtb fumarase is its similarity to the human homolog, which shares an identical active site. A potential solution to this selectivity problem was previously found in a high-throughput screening hit that binds in a nonconserved allosteric site. In this work, a structure-activity relationship study was carried out with the determination of further structural biology on the lead series, affording derivatives with sub-micromolar inhibition. Further, the screening of this series against Mtb in vitro identified compounds with potent minimum inhibitory concentrations.

SimpleDSFviewer: A tool to analyze and view differential scanning fluorimetry data for characterizing protein thermal stability and interactions

Differential scanning fluorimetry (DSF) is a widely used thermal shift assay for measuring protein stability and protein-ligand interactions that are simple, cheap, and amenable to high throughput. However, data analysis remains a challenge, requiring improved methods. Here, the program SimpleDSFviewer, a user-friendly interface, is described to help the researchers who apply DSF technique in their studies. SimpleDSFviewer integrates melting curve (MC) normalization, smoothing, and melting temperature (Tm) analysis and directly previews analyzed data, providing an efficient analysis tool for DSF. SimpleDSFviewer is developed in Matlab, and it is freely available for all users to use in Matlab workspace or with Matlab Runtime. It is easy to use and an efficient tool for researchers to preview and analyze their data in a very short time.

Sulfated polysaccharides interact with fibroblast growth factors and protect from denaturation

Fibroblast growth factors (FGFs) regulate embryonic development and homeostasis, including tissue and organ repair and specific aspects of metabolism. The basic FGF and acidic FGF, now known as FGF2 and FGF1, are widely used protein drugs for tissue repair. However, they are susceptible to denaturation at ambient temperatures and during long-time storage, which will reduce their biological activity. The interaction of FGFs with the sulfated domains of heparan sulfate and heparin is essential for their cellular signaling and stability. Therefore, we analyzed the interactions of FGF1 and FGF2 with four sulfated polysaccharides: heparin, dextran sulfate (DXS), λ-carrageenan, and chondroitin sulfate. The results of thermal stability and cell proliferation assays demonstrate that heparin, DXS, and λ-carrageenan bound to both FGFs and protected them from denaturation. Our results suggest heparin, DXS, and λ-carrageenan are potential formulation materials that bind and stabilize FGFs, and which may also potentiate their activity and control their delivery.

ATP-specificity of succinyl-CoA synthetase from Blastocystis hominis

Succinyl-CoA synthetase (SCS) catalyzes the only step of the tricarboxylic acid cycle that leads to substrate-level phosphorylation. Some forms of SCS are specific for ADP/ATP or for GDP/GTP, while others can bind all of these nucleotides, generally with different affinities. The theory of `gatekeeper' residues has been proposed to explain the nucleotide-specificity. Gatekeeper residues lie outside the binding site and create specific electrostatic interactions with incoming nucleotides to determine whether the nucleotides can enter the binding site. To test this theory, the crystal structure of the nucleotide-binding domain in complex with Mg²⁺-ADP was determined, as well as the structures of four proteins with single mutations, K46βE, K114βD, V113βL and L227βF, and one with two mutations, K46βE/K114βD. The crystal structures show that the enzyme is specific for ADP/ATP because of interactions between the nucleotide and the binding site. Nucleotide-specificity is provided by hydrogen-bonding interactions between the adenine base and Gln20β, Gly111β and Val113β. The O atom of the side chain of Gln20β interacts with N6 of ADP, while the side-chain N atom interacts with the carbonyl O atom of Gly111β. It is the different conformations of the backbone at Gln20β, of the side chain of Gln20β and of the linker that make the enzyme ATP-specific. This linker connects the two subdomains of the ATP-grasp fold and interacts differently with adenine and guanine bases. The mutant proteins have similar conformations, although the L227βF mutant shows structural changes that disrupt the binding site for the magnesium ion. Although the K46βE/K114βD double mutant of Blastocystis hominis SCS binds GTP better than ATP according to kinetic assays, only the complex with Mg²⁺-ADP was obtained.

TSA-CRAFT: A Free Software for Automatic and Robust Thermal Shift Assay Data Analysis

Thermal shift assay (TSA) is an increasingly popular technique used for identifying protein stabilizing conditions or interacting ligands in X-ray crystallography and drug discovery applications. Although the setting up and running of TSA reactions is a relatively simple process, the subsequent analysis of TSA data, especially in high-throughput format, requires substantial amount of effort if conducted manually. We therefore developed the Thermal Shift Assay-Curve Rapid and Automatic Fitting Tool (TSA-CRAFT), a freely available software that enable automatic analysis of TSA data of any throughput. TSA-CRAFT directly reads real-time PCR instrument data files and displays the analyzed results in a web browser. This software features streamlined data processing and Boltzmann equation fitting, which is demonstrated in this study to provide more accurate data analysis than the commonly used first-derivative method. TSA-CRAFT is freely available as a cross-operating system-compatible standalone tool ( https://sourceforge.net/projects/tsa-craft/ ) and also as a freely accessible web server ( http://tbtlab.org/tsacraft.html ).

nanoDSF as screening tool for enzyme libraries and biotechnology development

Enzymes are attractive tools for synthetic applications. To be viable for industrial use, enzymes need sufficient stability towards the desired reaction conditions such as high substrate and cosolvent concentration, non-neutral pH and elevated temperatures. Thermal stability is an attractive feature not only because it allows for protein purification by thermal treatment and higher process temperatures but also due to the associated higher stability against other destabilising factors. Therefore, high-throughput screening (HTS) methods are desirable for the identification of thermostable biocatalysts by discovery from nature or by protein engineering but current methods have low throughput and require time-demanding purification of protein samples. We found that nanoscale differential scanning fluorimetry (nanoDSF) is a valuable tool to rapidly and reliably determine melting points of native proteins. To avoid intrinsic problems posed by crude protein extracts, hypotonic extraction of overexpressed protein from bacterial host cells resulted in higher sample quality and accurate manual determination of several hundred melting temperatures per day. We have probed the use of nanoDSF for HTS of a phylogenetically diverse aldolase library to identify novel thermostable enzymes from metagenomic sources and for the rapid measurements of variants from saturation mutagenesis. The feasibility of nanoDSF for the screening of synthetic reaction conditions was proved by studies of cosolvent tolerance, which showed protein melting temperature to decrease linearly with increasing cosolvent concentration for all combinations of six enzymes and eight water-miscible cosolvents investigated, and of substrate affinity, which showed stabilisation of hexokinase by sugars in the absence of ATP cofactor. ENZYMES: Alcohol dehydrogenase (NADP⁺ ) (EC 1.1.1.2), transketolase (EC 2.2.1.1), hexokinase (EC 2.7.1.1), 2-deoxyribose-5-phosphate aldolase (EC 4.1.2.4), fructose-6-phosphate aldolase (EC 4.1.2.n).

Biophysical insights into a highly selective l-arginine-binding lipoprotein of a pathogenic treponeme

Biophysical and biochemical studies on the lipoproteins and other periplasmic proteins from the spirochetal species Treponema pallidum have yielded numerous insights into the functioning of the organism's peculiar membrane organization, its nutritional requirements, and intermediary metabolism. However, not all T. pallidum proteins have proven to be amenable to biophysical studies. One such recalcitrant protein is Tp0309, a putative polar-amino-acid-binding protein of an ABC transporter system. To gain further information on its possible function, a homolog of the protein from the related species T. vincentii was used as a surrogate. This protein, Tv2483, was crystallized, resulting in the determination of its crystal structure at a resolution of 1.75 Å. The protein has a typical fold for a ligand-binding protein, and a single molecule of l-arginine was bound between its two lobes. Differential scanning fluorimetry and isothermal titration calorimetry experiments confirmed that l-arginine bound to the protein with unusually high selectivity. However, further comparison to Tp0309 showed differences in key amino-acid-binding residues may impart an alternate specificity for the T. pallidum protein.

The calcium-binding site of human glutamate carboxypeptidase II is critical for dimerization, thermal stability, and enzymatic activity

Calcium ions are required for proper function of a wide spectrum of proteins within cells. X-ray crystallography of human glutamate carboxypeptidase II (GCPII) revealed the presence of a Ca²⁺ -binding site, but its importance for the structure and function of this metallopeptidase has not been elucidated to date. Here, we prepared a panel of mutants targeting residues that form the Ca²⁺ coordination sphere of GCPII and analyzed their structural and enzymatic properties using an array of complementary biophysical and biochemical approaches. Our data unequivocally show that even a slight disruption of the Ca²⁺ -binding site destabilizes the three-dimensional fold of GCPII and is associated with impaired secretion, a high propensity to form nonphysiological oligomers, and an inability to bind active site-targeted ligands. Additionally, the Ca²⁺ -binding site is critical for maintenance of the native homodimeric quaternary arrangement of GCPII, which is indispensable for its enzymatic activity. Overall, our results offer a clear picture of the importance of Ca²⁺ for the structural integrity and hydrolytic activity of human GCPII and by extension homologous members of the M28 zinc-dependent metallopeptidase family.

Persulfide Dioxygenase From Acidithiobacillus caldus: Variable Roles of Cysteine Residues and Hydrogen Bond Networks of the Active Site

Persulfide dioxygenases (PDOs) are abundant in Bacteria and also crucial for H2S detoxification in mitochondria. One of the two pdo-genes of the acidophilic bacterium Acidithiobacillus caldus was expressed in Escherichia coli. The protein (AcPDO) had 0.77 ± 0.1 Fe/subunit and an average specific sulfite formation activity of 111.5 U/mg protein (Vmax) at 40°C and pH 7.5 with sulfur and GSH following Michaelis-Menten kinetics. KM for GSH and Kcat were 0.5 mM and 181 s-1, respectively. Glutathione persulfide (GSSH) as substrate gave a sigmoidal curve with a Vmax of 122.3 U/mg protein, a Kcat of 198 s-1 and a Hill coefficient of 2.3 ± 0.22 suggesting positive cooperativity. Gel permeation chromatography and non-denaturing gels showed mostly tetramers. The temperature optimum was 40-45°C, the melting point 63 ± 1.3°C in thermal unfolding experiments, whereas low activity was measurable up to 95°C. Site-directed mutagenesis showed that residues located in the predicted GSH/GSSH binding site and in the central hydrogen bond networks including the iron ligands are essential for activity. Among these, the R139A, D141A, and H171A variants were inactive concomitant to a decrease of their melting points by 3-8 K. Other variants were inactivated without significant melting point change. Two out of five cysteines are likewise essential, both of which lie presumably in close proximity at the surface of the protein (C87 and C224). MalPEG labeling experiments suggests that they form a disulfide bridge. The reducing agent Tris(2-carboxyethyl)phosphine was inhibitory besides N-ethylmaleimide and iodoacetamide suggesting an involvement of cysteines and the disulfide in catalysis and/or protein stabilization. Mass spectrometry revealed modification of C87, C137, and C224 by 305 mass units equivalent to GSH after incubation with GSSH and with GSH in case of the C87A and C224A variants. The results of this study suggest that disulfide formation between the two essential surface-exposed cysteines and Cys-S-glutathionylation serve as a protective mechanism against uncontrolled thiol oxidation and the associated loss of enzyme activity.

Bacterial Expression of Human Butyrylcholinesterase as a Tool for Nerve Agent Bioscavengers Development

Human butyrylcholinesterase is a performant stoichiometric bioscavenger of organophosphorous nerve agents. It is either isolated from outdated plasma or functionally expressed in eukaryotic systems. Here, we report the production of active human butyrylcholinesterase in a prokaryotic system after optimization of the primary sequence through the Protein Repair One Stop Shop process, a structure- and sequence-based algorithm for soluble bacterial expression of difficult eukaryotic proteins. The mutant enzyme was purified to homogeneity. Its kinetic parameters with substrate are similar to the endogenous human butyrylcholinesterase or recombinants produced in eukaryotic systems. The isolated protein was prone to crystallize and its 2.5-Å X-ray structure revealed an active site gorge region identical to that of previously solved structures. The advantages of this alternate expression system, particularly for the generation of butyrylcholinesterase variants with nerve agent hydrolysis activity, are discussed.

Combining Fungicides and Prospective NPR1-Based "Just-in-Time" Immunomodulating Chemistries for Crop Protection

Each year, crop yield is lost to weeds competing for resources, insect herbivory and diseases caused by pathogens. To thwart these insults and preserve yield security and a high quality of traits, conventional agriculture makes use of improved cultivars combined with fertilizer and agrochemical applications. However, given that regulatory bodies and consumers are demanding environmentally safer agrochemicals, while at the same time resistance to agrochemicals is mounting, it is crucial to adopt a "holistic" approach to agriculture by not excluding any number of management tools at our disposal. One such tool includes chemicals that stimulate plant immunity. The development of this particular type of alternative crop protection strategy has been of great interest to us. We have approached this paradigm by studying plant immunity, specifically systemic acquired resistance (SAR). The deployment of SAR immunity requires the production by the crop plant of an endogenous small molecule metabolite called salicylic acid (SA). Furthermore, immunity can only be deployed if SA can bind to its receptor and activate the genes responsible for the SAR program. The key receptor for SAR is a transcription coactivator called NPR1. Since discovering this NPR1-SA receptor-ligand pair, we have embarked on a journey to develop novel chemistries capable of deploying SAR in the field. The journey begins with the development of a scalable assay to identify these novel chemistries. One such assay, presented here, is based on differential scanning fluorimetry technology and demonstrates that NPR1 is destabilized by binding to SA.

Thermal Stability as a Determinant of AAV Serotype Identity

Currently, there are over 150 ongoing clinical trials utilizing adeno-associated viruses (AAVs) to target various genetic diseases, including hemophilia (AAV2 and AAV8), congenital heart failure (AAV1 and AAV6), cystic fibrosis (AAV2), rheumatoid arthritis (AAV2), and Batten disease (AAVrh.10). Prior to patient administration, AAV vectors must have their serotype, concentration, purity, and stability confirmed. Here, we report the application of differential scanning fluorimetry (DSF) as a good manufacturing practice (GMP) capable of determining the melting temperature (Tm) for AAV serotype identification. This is a simple, rapid, cost effective, and robust method utilizing small amounts of purified AAV capsids (∼25 μL of ∼1011 particles). AAV1-9 and AAVrh.10 exhibit specific Tms in buffer formulations commonly used in clinical trials. Notably, AAV2 and AAV3, which are the least stable, have varied Tms, whereas AAV5, the most stable, has a narrow Tm range in the different buffers, respectively. Vector stability was dictated by VP3 only, specifically, the ratio of basic/acidic amino acids, and was independent of VP1 and VP2 content or the genome packaged. Furthermore, stability of recombinant AAVs differing by a single basic or acidic amino acid residue are distinguishable. Hence, AAV DSF profiles can serve as a robust method for serotype identification of clinical vectors.

Evaluation of compound selectivity of aldo-keto reductases using differential scanning fluorimetry

Inhibitors of AKR1B10 belonging to the aldo-keto reductase (AKR) superfamily are considered promising candidates for anti-cancer drugs. AKR1B1, a structurally similar isoform of AKR1B10, is involved in glucose metabolism. Thus, selective inhibition of AKR1B10 is required for the development of anti-cancer drugs. In this study, we first compared correlations between melting temperature and the 50% inhibition concentration obtained from differential scanning fluorimetry (DSF) and an enzyme inhibitory experiment, respectively, and a good correlation was found, except for compounds with low solubility. This result indicates that the DSF method is useful for drug screening for the AKR superfamily. We then evaluated their selectivity as inhibitors against all seven major human AKR1 family proteins and found that C18 is most specific for AKR1B10.

Functional clues from the crystal structure of an orphan periplasmic ligand-binding protein from Treponema pallidum

The spirochete Treponema pallidum is the causative agent of syphilis, a sexually transmitted infection of major global importance. Other closely related subspecies of Treponema also are the etiological agents of the endemic treponematoses, such as yaws, pinta, and bejel. The inability of T. pallidum and its close relatives to be cultured in vitro has prompted efforts to characterize T. pallidum's proteins structurally and biophysically, particularly those potentially relevant to treponemal membrane biology, with the goal of possibly revealing the functions of those proteins. This report describes the structure of the treponemal protein Tp0737; this polypeptide has a fold characteristic of a class of periplasmic ligand-binding proteins associated with ABC-type transporters. Although no ligand for the protein was observed in electron-density maps, and thus the nature of the native ligand remains obscure, the structural data described herein provide a foundation for further efforts to elucidate the ligand and thus the function of this protein in T. pallidum.

Stabilization of tryptophan hydroxylase 2 by l-phenylalanine-induced dimerization

Tryptophan hydroxylase 2 (TPH2) catalyses the initial and rate‐limiting step in the biosynthesis of serotonin, which is associated with a variety of disorders such as depression, obsessive compulsive disorder, and schizophrenia. Full‐length TPH2 is poorly characterized due to low purification quantities caused by its inherent instability. Three truncated variants of human TPH2 (rchTPH2; regulatory and catalytic domain, NΔ47‐rchTPH2; truncation of 47 residues in the N terminus of rchTPH2, and chTPH2; catalytic domain) were expressed, purified, and examined for changes in transition temperature, inactivation rate, and oligomeric state. chTPH2 displayed 14‐ and 11‐fold higher half‐lives compared to rchTPH2 and NΔ47‐rchTPH2, respectively. Differential scanning calorimetry experiments demonstrated that this is caused by premature unfolding of the less stable regulatory domain. By differential scanning fluorimetry, the unfolding transitions of rchTPH2 and NΔ47‐rchTPH2 are found to shift from polyphasic to apparent two‐state by the addition of l‐Trp or l‐Phe. Analytical gel filtration revealed that rchTPH2 and NΔ47‐rchTPH2 reside in a monomer–dimer equilibrium which is significantly shifted toward dimer in the presence of l‐Phe. The dimerizing effect induced by l‐Phe is accompanied by a stabilizing effect, which resulted in a threefold increase in half‐lives of rchTPH2 and NΔ47‐rchTPH2. Addition of l‐Phe to the purification buffer significantly increases the purification yields, which will facilitate characterization of hTPH2.

The influence of angiotensin converting enzyme mutations on the kinetics and dynamics of N-domain selective inhibition

Angiotensin-1-converting enzyme (ACE) is a zinc metalloprotease that plays a major role in blood pressure regulation via the renin-angiotensin-aldosterone system. ACE consists of two domains with differences in inhibitor binding affinities despite their 90% active site identity. While the C-domain primarily controls blood pressure, the N-domain is selective for cleavage of the antifibrotic N-acetyl-Ser-Asp-Lys-Pro. Inhibitors, such as 33RE, that selectively bind to the N-domain thus show potential for treating fibrosis without affecting blood pressure. The aim of this study was to elucidate the molecular mechanism of this selectivity. ACE inhibition by 33RE was characterized using a continuous kinetic assay with fluorogenic substrate. The N-domain displayed nanomolar (K_i = 11.21 ± 0.74 nm) and the C-domain micromolar (K_i = 11 278 ± 410 nm) inhibition, thus 1000-fold selectivity. Residues predicted to contribute to selectivity based on the N-domain-33RE co-crystal structure were subsequently mutated to their C-domain counterparts. S₂ subsite mutation with resulting loss of a hydrogen bond drastically decreased the affinity (K_i = 2 794 ± 156 nm), yet did not entirely account for selectivity. Additional substitution of all unique S₂ ' residues, however, completely abolished selectivity (K_i = 10 009 ± 157 nm). Interestingly, these residues do not directly bind 33RE. All mutants were therefore subjected to molecular dynamics simulations in the presence and absence of 33RE. Trajectory analyses highlighted the importance of these S₂ ' residues in formation of a favourable interface between the ACE subdomains and thus a closed, ligand-bound complex. This study provides a molecular basis for the intersubsite synergism governing 33RE's 1000-fold N-selectivity and aids the future design of novel inhibitors for fibrosis treatment.

ENZYMES

Angiotensin converting enzyme (ACE, EC 3.4.15.1).

Structure of an ABC transporter solute-binding protein specific for the amino sugars glucosamine and galactosamine

The uptake of exogenous solutes by prokaryotes is mediated by transport systems embedded in the plasma membrane. In many cases, a solute-binding protein (SBP) is utilized to bind ligands with high affinity and deliver them to the membrane-bound components responsible for translocation into the cytoplasm. In the present study, Avi_5305, an Agrobacterium vitis SBP belonging to Pfam13407, was screened by differential scanning fluorimetry (DSF) and found to be stabilized by D-glucosamine and D-galactosamine. Avi_5305 is the first protein from Pfam13407 shown to be specific for amino sugars, and co-crystallization resulted in structures of Avi_5305 bound to D-glucosamine and D-galactosamine. Typical of Pfam13407, Avi_5305 consists of two α/β domains linked through a hinge region, with the ligand-binding site located in a cleft between the two domains. Comparisons with Escherichia coli ribose-binding protein suggest that a cation-π interaction with Tyr168 provides the specificity for D-glucosamine/D-galactosamine over D-glucose/D-galactose.

Maltase protein of Ogataea (Hansenula) polymorpha is a counterpart to the resurrected ancestor protein ancMALS of yeast maltases and isomaltases

Saccharomyces cerevisiae maltases use maltose, maltulose, turanose and maltotriose as substrates, isomaltases use isomaltose, α‐methylglucoside and palatinose and both use sucrose. These enzymes are hypothesized to have evolved from a promiscuous α‐glucosidase ancMALS through duplication and mutation of the genes. We studied substrate specificity of the maltase protein MAL1 from an earlier diverged yeast, Ogataea polymorpha (Op), in the light of this hypothesis. MAL1 has extended substrate specificity and its properties are strikingly similar to those of resurrected ancMALS. Moreover, amino acids considered to determine selective substrate binding are highly conserved between Op MAL1 and ancMALS. Op MAL1 represents an α‐glucosidase in which both maltase and isomaltase activities are well optimized in a single enzyme. Substitution of Thr200 (corresponds to Val216 in S. cerevisiae isomaltase IMA1) with Val in MAL1 drastically reduced the hydrolysis of maltose‐like substrates (α‐1,4‐glucosides), confirming the requirement of Thr at the respective position for this function. Differential scanning fluorimetry (DSF) of the catalytically inactive mutant Asp199Ala of MAL1 in the presence of its substrates and selected monosaccharides suggested that the substrate‐binding pocket of MAL1 has three subsites (–1, +1 and +2) and that binding is strongest at the –1 subsite. The DSF assay results were in good accordance with affinity (K_m) and inhibition (K_i) data of the enzyme for tested substrates, indicating the power of the method to predict substrate binding. Deletion of either the maltase (MAL1) or α‐glucoside permease (MAL2) gene in Op abolished the growth of yeast on MAL1 substrates, confirming the requirement of both proteins for usage of these sugars. © 2016 The Authors. Yeast published by John Wiley & Sons, Ltd.

Discovery of Strecker-type α-aminonitriles as a new class of human carbonic anhydrase inhibitors using differential scanning fluorimetry

A new type of carbonic anhydrase inhibitors was identified via differential scanning fluorimetry (DSF) screening. The compounds displayed interesting inhibition profile against human carbonic anhydrase isoforms I, II, IX and XII with an obvious selectivity displayed by one compound toward carbonic anhydrase (CA) IX, an established anti-cancer target. A hypothetical mechanism of inhibitory action by the Strecker-type α-aminonitriles has been proposed.

Formulation screening by differential scanning fluorimetry: how often does it work?

There is strong evidence to suggest that a protein sample needs to be well folded and uniform in order to form protein crystals, and it is accepted knowledge that the formulation can have profound effects on the behaviour of the protein sample. The technique of differential scanning fluorimetry (DSF) is a very accessible method to determine protein stability as a function of the formulation chemistry and the temperature. A diverse set of 252 soluble protein samples was subjected to a standard formulation-screening protocol using DSF. Automated analysis of the DSF results suggest that in over 35% of cases buffer screening significantly increases the stability of the protein sample. Of the 28 standard formulations tested, three stood out as being statistically better than the others: these included a formulation containing the buffer citrate, long known to be `protein friendly'; bis-tris and ADA were also identified as being very useful buffers in protein formulations.