Unbound Protein Research Articles

Intra- or extra-exosomal secretion of HDGF isoforms: the extraordinary function of the HDGF-A N-terminal peptide.

Hepatoma-derived growth factor (HDGF) is a protein with diverse intracellular functions. Moreover, after non-conventional secretion, extracellular HDGF is able to influence different signaling pathways, leading for example to induction of processes like epithelial-mesenchymal transition (EMT) and cell migration. Intriguingly, in recent proteome studies, HDGF was also found secreted by special microvesicles called exosomes. Recently, we demonstrated the existence of two new HDGF isoforms (B and C). These isoforms are involved in different cellular processes than HDGF-A. Along this line, in the present study we discovered that full length HDGF-A clearly is located inside of exosomes, whereas the isoforms HDGF-B and HDGF-C are found exclusively on the outer surface. Furthermore, while HDGF-B and HDGF-C seem to use exosomes mediated pathway exclusively, HDGF-A was found also as unbound protein in the conditioned media. The new finding of an intra- or extra-exosomal localisation of protein splice variants opens a fascinating new perspective concerning functional diversity of HDGF isoforms. Dysregulation of HDGF expression during cancer development and tumor progression is a commonly known fact. With our new findings, unraveling the potential functional impact according to physiological versus pathophysiologically altered levels and compositions of intra- and extra-exosomal HDGF has to be addressed in future studies.

Paradoxical effects of SAA on lipoprotein oxidation suggest a new antioxidant function for SAA

Oxidative stress and inflammation, which involve a dramatic increase in serum amyloid A (SAA) levels, are critical in the development of atherosclerosis. Most SAA circulates on plasma HDL particles, altering their cardioprotective properties. SAA-enriched HDL has diminished anti-oxidant effects on LDL, which may contribute to atherogenesis. We determined combined effects of SAA enrichment and oxidation on biochemical changes in HDL. Normal human HDLs were incubated with SAA, oxidized by various factors (Cu2+, myeloperoxidase, H2O2, OCl-), and analyzed for lipid and protein modifications and biophysical remodeling. Three novel findings are reported: addition of SAA reduces oxidation of HDL and LDL lipids; oxidation of SAA-containing HDL in the presence of OCl- generates a covalent heterodimer of SAA and apoA-I that resists the release from HDL; and mild oxidation promotes spontaneous release of proteins (SAA and apoA-I) from SAA-enriched HDL. We show that the anti-oxidant effects of SAA extend to various oxidants and are mediated mainly by the unbound protein. We propose that free SAA sequesters lipid hydroperoxides and delays lipoprotein oxidation, though much less efficiently than other anti-oxidant proteins, such as apoA-I, that SAA displaces from HDL. These findings prompt us to reconsider the role of SAA in lipid oxidation in vivo.

GENIUS In Silico Screening Technology for HCV Drug Discovery.

The various reported in silico screening protocols such as molecular docking are associated with various drawbacks as well as benefits. In molecular docking, on interaction with ligand, the protein or receptor molecule gets activated by adopting conformational changes. These conformational changes cannot be utilized to predict the 3D structure of a protein-ligand complex from unbound protein conformations rigid docking, which necessitates the demand for understanding protein flexibility. Therefore, efficiency and accuracy of docking should be achieved and various available/developed protocols may be adopted. One such protocol is GENIUS induced-fit docking and it is used effectively for the development of anti-HCV NS3-4A serine protease inhibitors. The present review elaborates the GENIUS docking protocol along with its benefits and drawbacks.

Enrichment of Two Isomeric Heparin Oligosaccharides Exhibiting Different Affinities toward Monocyte Chemoattractant Protein-1.

Chemokine-GAG interactions are crucial to facilitate chemokine immobilization, resulting in the formation of chemokine gradients that guide cell migration. Here we demonstrate chromatographic isolation and purification of two heparin hexasaccharide isomers that interact with the oligomeric chemokine Monocyte Chemoattractant Protein-1 (MCP-1)/CCL2 with different binding affinities. The sequences of these two hexasaccharides were deduced from unique MS/MS product ions and HPLC compositional analysis. Ion mobility mass spectrometry (IM-MS) showed that the two isolated oligosaccharides have different conformations and both displayed preferential binding for one of the two distinct conformations known for MCP-1 dimers. A significant shift in arrival time distribution of close to 70 Å2 was observed, indicating a more compact protein:hexasaccharide conformation. Clear differences in the MS spectra between bound and unbound protein allowed calculation of Kd values from the resulting data. The structural difference between the two hexasaccharides was defined as the differential location of a single sulfate at either C-6 of glucosamine or C-2 of uronic acid in the reducing disaccharide, resulting in a 200-fold difference in binding affinity for MCP-1. These data indicate sequence specificity for high affinity binding, supporting the view that sulfate position, and not simply the number of sulfates, is important for heparan sulfate protein binding.

Protein-RNA interactions: structural biology and computational modeling techniques.

RNA-binding proteins are functionally diverse within cells, being involved in RNA-metabolism, translation, DNA damage repair, and gene regulation at both the transcriptional and post-transcriptional levels. Much has been learnt about their interactions with RNAs through structure determination techniques and computational modeling. This review gives an overview of the structural data currently available for protein-RNA complexes, and discusses the technical issues facing structural biologists working to solve their structures. The review focuses on three techniques used to solve the 3-dimensional structure of protein-RNA complexes at atomic resolution, namely X-ray crystallography, solution nuclear magnetic resonance (NMR) and cryo-electron microscopy (cryo-EM). The review then focuses on the main computational modeling techniques that use these atomic resolution data: discussing the prediction of RNA-binding sites on unbound proteins, docking proteins, and RNAs, and modeling the molecular dynamics of the systems. In conclusion, the review looks at the future directions this field of research might take.

Immunoaffinity chromatography in antivenomics studies: Various parameters that can affect the results

Antivenomics is a recently developed powerful method for the study of antivenom antibody profiles when bound to homologous and heterologous snake venoms. The information obtained is useful in gaining an understanding of venom protein immunogenicity, antivenom potency and also for the improvement of antivenom potency and paraspecificity. The preferred method used in this type of study is immunoaffinity chromatography of the venom proteins on an antivenom IgG (or F(ab′)2) column where the bound and unbound proteins can be separated and identified. However, there are some parameters of the immunochromatography that can significantly affect the binding of the proteins to the immunoaffinity matrix and lead to imprecise results in antivenom immunoprofiling. The present study demonstrated that the ligand density (mg IgG/ml of the matrix), the buffers used for binding and washing the venom proteins, the amount of venom loaded, the abundance of some venom protein(s) and the eluting buffers can significantly alter the binding of the proteins to the matrix and consequently the conclusions drawn from antivenomics studies. Furthermore, the immunochromatographic procedure can be extended to include the estimation of the relative affinity of venom protein-antibody interactions that can provide additional information useful to antivenomics study.

Partial denaturation of recombinant protein for affinity purification

In this study, we investigate the absence of binding between the 6-His-tagged human transthyretin–green fluorescent protein fusion and the affinity sorbent. Also, the proposal that a partial conformational change makes the 6-His sequence sterically inaccessible and prevents its incorporation into the nickel ion coordination sphere is confirmed. After prolonged incubation (4 weeks) in the presence of imidazole, the protein almost completely lost its capability of binding with Ni-agarose. The treatment of the unbound protein fraction with 0.5 M guanidine hydrochloride recovered this capability. Notably, the recovered protein was in regular conformation and had no signs of denaturation. This approach of partial denaturation resulting in the melted globule can be used for the affinity purification of other recombinant proteins synthesized in bacterial systems, when they are incapable of binding with affinity sorbents or can be solubilized only in the presence of denaturing agents.

Discrimination of Glycoproteins from Unglycosylated Proteins in Capillary Electrophoresis: Two-Color LIF Detection Coupled with Post-column Derivatization.

Glycosylation is one of the most important posttranslational modifications (PTMs) which lead to the functionalization of proteins. Here, we describe one method for discriminating glycosylated proteins from unglycosylated ones in their mixture sample by capillary electrophoretic separation and two-color laser-induced fluorescence detection coupled with post-column derivatization. Two lasers emitting at 450 and 532 nm permit the detection of amino groups of proteins derivatized by naphthalene-2,3-dicarboxaldehyde and a fluorescently labeled lectin, tetramethylrhodamine-labeled concanavalin A (Rh-Con A), respectively. When a protein mixture react with Rh-Con A, the glycoproteins bound with Rh-Con A exhibit signals at the same migration time in two electropherograms obtained by 450- and 532-nm lasers whereas unbound proteins show a signal only in the electropherogram of the 450-nm laser. So, when one protein is glycosylated it is detected at the same migration time in the electropherograms obtained by two lasers.

DNA-Directed Assembly of Nanogold Dimers: A Unique Dynamic Light Scattering Sensing Probe for Transcription Factor Detection.

We have developed a unique DNA-assembled gold nanoparticles (AuNPs) dimer for dynamic light scattering (DLS) sensing of transcription factors, exemplified by estrogen receptor (ER) that binds specifically to a double-stranded (ds) DNA sequence containing estrogen response element (ERE). Here, ERE sequence is incorporated into the DNA linkers to bridge the AuNPs dimer for ER binding. Coupled with DLS, this AuNP dimer-based DLS detection system gave distinct readout of a single ‘complex peak’ in the presence of the target molecule (i.e., ER). This unique signature marked the first time that such nanostructures can be used to study transcription factor-DNA interactions, which DLS alone cannot do. This was also unlike previously reported AuNP-DLS assays that gave random and broad distribution of particles size upon target binding. In addition, the ERE-containing AuNP dimers could also suppress the light-scattering signal from the unbound proteins and other interfering factors (e.g., buffer background), and has potential for sensitive detection of target proteins in complex biological samples such as cell lysates. In short, the as-developed AuNP dimer probe coupled with DLS is a simple (mix and test), rapid (readout in ~5 min) and sensitive (low nM levels of ER) platform to detect sequence-specific protein-DNA binding event.

T3: Targeted proteomics of DNA-binding proteins

A technique that allows the inclusion of a specific DNA to enrich and direct proteomic identification of transcription factors (TFs) while providing a route for high-throughput screening on a single platform would be valuable in investigations of gene expression and regulation. Polyvinylpyrrolidone binds DNA avidly while binding negligible amounts of protein. This observation is used in a proof-of-concept method to enrich for TFs by combining nuclear extract with a specific DNA sequence and immobilizing the DNA–protein complex on a polyvinylpyrrolidone (PVP)-coated MALDI (matrix-assisted laser desorption/ionization) plate. Any unbound proteins are washed away and further processed for analysis in a MALDI–TOF/TOF (tandem time-of-flight) mass spectrometer. Enrichment on a PVP-coated plate gives the unique advantage of purification, enzymatic digestion, and analysis on a single platform. The method is termed T3 because it combines Targeted purification on a Target plate with Targeted proteomics. Validation was achieved in model experiments with a chimeric fusion protein, green fluorescent protein–CAAT enhancer binding protein (GFP-C/EBP), with an oligonucleotide containing the CAAT sequence. Both domains were identified with an expectation value of less than 10–15 and more than 15% sequence coverage. The same oligonucleotide mixed with HEK293 cell nuclear extract allowed the unambiguous identification of native human C/EBP alpha with 24.3% sequence coverage.

Abstract 1246: Development and validation of a global proteomics approach for identifying novel binding partners of resveratrol

Abstract The dietary constituent resveratrol (trans-3,5,4′-trihydroxystilbene) has received a great deal of scientific attention and publicity due to its broad ranging pharmacological effects in preclinical systems, including cancer chemoprevention in a variety of rodent carcinogenesis models. It has been hypothesized that resveratrol exerts its effects by interacting directly with specific proteins such as cyclooxygenase 2 (COX2) and NAD(P)H dehydrogenase quinone 2 (NQO2). Nevertheless the key targets which may mediate its anticancer activity in humans have not yet been identified. An affinity purification (pull-down) assay coupled with global LC-MS/MS analysis was developed to identify proteins that bind directly to resveratrol. Resveratrol was synthetically linked via one of its phenol moieties to agarose beads using a short amine linker, generating two resveratrol bead species. Resveratrol beads were incubated with cell lysate from human-derived colon adenocarcinoma (HCA7) or adenoma cells (AAC1) and then washed to remove unbound proteins. Resveratrol-bound proteins were eluted from the beads by heat denaturation in SDS buffer. Control beads end-capped with ethanolamine were used to identify non-specific protein binding. Proteins were eluted from the beads and identified in trypsinised gel slices by PAGE coupled with either LC-MS/MS to identify all proteins bound to resveratrol or immunoblotting to identify known target proteins. More than 30 proteins were identified by LC-MS/MS that were reproducibly ‘pulled’ from cell lysates by resveratrol beads. The proteins identified fall into five main groups, including enzymes and proteins associated with nuclear transport, apoptosis, DNA repair, prostaglandin and fatty acid synthesis. Following MS/MS, 30 proteins were confirmed as selective binding partners of resveratrol by Western blotting, with 97% agreement between the two detection methods. Among the proteins identified were COX2, NQO2, fatty acid synthase (FAS) and Exportin 1 (CRM1). The first two are known resveratrol targets, which supports the validity of the method. Resveratrol at clinically achievable concentrations (0.001-10 μM) did not change the expression of the proteins identified in the pull-down assay. It is conceivable that resveratrol modulates the function of the proteins to which it binds. To test this hypothesis the effects of resveratrol on FAS activity and on Exportin 1 and its cargoes is currently under investigation. In conclusion, the protein pull-down assay described here may help discover mechanism-related protein biomarkers that can be used to monitor the efficacy of multi-targeted cancer chemopreventive diet constituents in individuals in chemoprevention trials. Citation Format: Christina J. Kovoor, Robert G. Britton, Emma Horner-Glister, Catherine Andreadi, Raj Singh, Rebekah Jukes-Jones, Kelvin Cain, William P. Steward, Andreas Gescher, Karen Brown. Development and validation of a global proteomics approach for identifying novel binding partners of resveratrol. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1246. doi:10.1158/1538-7445.AM2014-1246

PH-dependent vesicle fusion induced by the ectodomain of the human immunodeficiency virus membrane fusion protein gp41: Two kinetically distinct processes and fully-membrane-associated gp41 with predominant β sheet fusion peptide conformation

The gp41 protein of the Human Immunodeficiency Virus (HIV) catalyzes fusion between HIV and host cell membranes. The ~180-residue ectodomain of gp41 is outside the virion and is the most important gp41 region for membrane fusion. The ectodomain consists of an apolar fusion peptide (FP) region hypothesized to bind to the host cell membrane followed by N-heptad repeat (NHR), loop, and C-heptad repeat (CHR) regions. The present study focuses on the large gp41 ectodomain constructs “Hairpin” (HP) containing NHR+loop+CHR and “FP–Hairpin” (FP–HP) containing FP+NHR+loop+CHR. Both proteins induce rapid and extensive fusion of anionic vesicles at pH4 where the protein is positively-charged but do not induce fusion at pH7 where the protein is negatively charged. This observation, along with lack of fusion of neutral vesicles at either pH supports the significance of attractive protein/membrane electrostatics in fusion. There are two kinetically distinct fusion processes at pH4: (1) a faster ~100ms−1 process with rate strongly positively correlated with vesicle charge; and (2) a slower ~5ms−1 process with extent strongly inversely correlated with this charge. The slower process may be more physiologically relevant because HIV/host cell fusion occurs at physiologic pH with gp41 restricted to the narrow region between the two membranes. Previous solid-state NMR (SSNMR) of membrane-associated FP–HP has supported protein oligomers with FP's in an intermolecular antiparallel sheet. There was an additional population of molecules with α helical FPs and the samples likely contained a mixture of membrane-bound and -unbound proteins. For the present study, samples were prepared with fully membrane-bound FP–HP and subsequent SSNMR showed dominant β FP conformation at both low and neutral pH. SSNMR also showed close contact of the FP with the lipid headgroups at both low and neutral pH whereas the NHR+CHR regions had contact at low pH and were more distant at neutral pH, consistent with the protein/membrane electrostatics. This article is part of a Special Issue entitled:NMR Spectroscopy for Atomistic Views of Biomembranes and Cell Surfaces. Guest Editors: Lynette Cegelski and David P. Weliky.

Protein expression and purification

Production of recombinant proteins is essential for many applications in both basic research and also in medicine, where recombinant proteins are used as pharmaceuticals. This review summarizes procedures involved in recombinant protein expression and purification, including molecular cloning of target genes into expression vectors, selection of the appropriate expression system, and protein purification techniques. Recombinant DNA technology allows protein engineering to modify protein stability, activity and function or to facilitate protein purification by affinity tag fusions. A wide range of cloning systems enabling fast and effective design of expression vectors is currently available. A first choice of protein expression system is usually the bacteria Escherichia coli. The main advantages of this prokaryotic expression system are low cost and simplicity; on the other hand this system is often unsuitable for production of complex mammalian proteins. Protein expression mediated by eukaryotic cells (yeast, insect and mammalian cells) usually produces properly folded and posttranslationally modified proteins. How-ever, cultivation of insect and, especially, mammalian cells is time consuming and expensive. Affinity tagged recombinant proteins are purified efficiently using affinity chromatography. An affinity tag is a protein or peptide that mediates specific binding to a chromatography column, unbound proteins are removed during a washing step and pure protein is subsequently eluted.

Identification of New IκBα Complexes by an Iterative Experimental and Mathematical Modeling Approach

The transcription factor nuclear factor kappa-B (NFκB) is a key regulator of pro-inflammatory and pro-proliferative processes. Accordingly, uncontrolled NFκB activity may contribute to the development of severe diseases when the regulatory system is impaired. Since NFκB can be triggered by a huge variety of inflammatory, pro-and anti-apoptotic stimuli, its activation underlies a complex and tightly regulated signaling network that also includes multi-layered negative feedback mechanisms. Detailed understanding of this complex signaling network is mandatory to identify sensitive parameters that may serve as targets for therapeutic interventions. While many details about canonical and non-canonical NFκB activation have been investigated, less is known about cellular IκBα pools that may tune the cellular NFκB levels. IκBα has so far exclusively been described to exist in two different forms within the cell: stably bound to NFκB or, very transiently, as unbound protein. We created a detailed mathematical model to quantitatively capture and analyze the time-resolved network behavior. By iterative refinement with numerous biological experiments, we yielded a highly identifiable model with superior predictive power which led to the hypothesis of an NFκB-lacking IκBα complex that contains stabilizing IKK subunits. We provide evidence that other but canonical pathways exist that may affect the cellular IκBα status. This additional IκBα:IKKγ complex revealed may serve as storage for the inhibitor to antagonize undesired NFκB activation under physiological and pathophysiological conditions.

Chromatin Fractionation Assay in Fission Yeast

The protein recruitment onto chromatin is a critical process for DNA metabolism, including DNA replication, DNA repair and DNA recombination. Especially DNA modification enzymes and checkpoint proteins are loaded onto DNA damage sites in a context-dependent manner. In our recent study (Kunoh and Habu, 2014), the chromatin association of Pcf1, a large subunit of Chromatin Assembly Factor-1 (CAF-1), was monitored after exposure of cells to hydroxyurea which slowed down the DNA replication. Results of the chromatin fractionation assay provided evidence that Pcf1 was recruited to chromatin upon DNA replication stress. A similar procedure enabled to reveal the chromatin association of Orp1, Mcm proteins, and Swi6 (Sadaie et al., 2008; Ogawa et al., 1999). This assay allows us to fractionate chromatin-bound and -unbound proteins from living cells. The following immunoblot of the respective fractions provides the information concerning the chromatin binding status of our target proteins.

In Silico Insight into Potent of Anthocyanin Regulation of FKBP52 to Prevent Alzheimer's Disease.

Alzheimer's disease (AD) is caused by the hyperphosphorylation of Tau protein aggregation. FKBP52 (FK506 binding protein 52) has been found to inhibit Tau protein aggregation. This study found six different kinds of anthocyanins that have high binding potential. After analyzing the docking positions, hydrophobic interactions, and hydrogen bond interactions, several amino acids were identified that play important roles in protein and ligand interaction. The proteins' variation is described using eigenvectors and the distance between the amino acids during a molecular dynamics simulation (MD). This study investigates the three loops based around Glu85, Tyr113, and Lys121—all of which are important in inducing FKBP52 activation. By performing a molecular dynamic simulation process between unbound proteins and the protein complex with FK506, it was found that ligand targets that docked onto the FK1 domain will decrease the distance between Glu85/Tyr113 and Glu85/Lys121. The FKBP52 structure variation may induce FKBP52 activation and inhibit Tau protein aggregation. The results indicate that anthocyanins might change the conformation of FKBP52 during binding. In addition, the purple anthocyanins, such as cyanidin-3-glucoside and malvidin-3-glucoside, might be better than FK506 in regulating FKBP52 and treating Alzheimer's disease.

Experimental and Simulation Studies on the Mechanical Properties of Sumo Proteins

Protein structure plays an important role in determining its mechanical stability. In order to understand the role of amino acid sequence on the mechanical stability, mechanical unfolding experiments were performed using atomic force microscope based single-molecule force spectroscopy (SMFS) on structurally homologous proteins - ubiquitin, SUMO1, and SUMO2. SUMOs are found to be mechanically weaker than ubiquitin, in spite of their high structural homology, when pulled along N-C direction [1]. The unfolding forces of these proteins follow the same trend as the number of sidechain contacts within them. The energy landscape parameters reveal that SUMOs are more flexible than ubiquitin. We have performed steered molecular dynamics simulations on these proteins to gain atomistic insights into their unfolding pathways. The hydrogen bonds in the mechanical clamp between the terminal β-strands of these proteins are ruptured at the transtion state and proteins unfolded in an all-or-none fashion. The interactions between the β2 strand and the α-helix also weaken at the transition state. We examine the different types of inter-resiude interactions in these proteins to rationalize the lower mechanical stability of SUMOs relative to ubiquitin. Role of water penetration during mechanical unfolding was also investigated.We have further studied the effect of ligand binding on the mechanical stability of SUMO proteins using SMFS in presence of short peptides derived from the binding motifs of SUMO targets. The unfolding force of SUMO1 increased from ∼130pN to ∼170pN upon ligand binding. Dependence of the unfolding force on the pulling speed was higher for SUMO1 bound to the peptides than the unbound protein. The flexibility of SUMOs decreased upon ligand binding suggesting a possible role of SUMO flexibility in SUMOylation.[1] Kotamarthi HC, Sharma R, Ainavarapu SRK, Biophys. J (2013), 104, p2273.

The role of the C-terminal helix of U1A protein in the interaction with U1hpII RNA

Previous kinetic investigations of the N-terminal RNA Recognition Motif (RRM) domain of spliceosomal A protein of the U1 small nuclear ribonucleoprotein particle (U1A) interacting with its RNA target U1 hairpin II (U1hpII) provided experimental evidence for a ‘lure and lock’ model of binding. The final step of locking has been proposed to involve conformational changes in an α-helix immediately C-terminal to the RRM domain (helix C), which occludes the RNA binding surface in the unbound protein. Helix C must shift its position to accommodate RNA binding in the RNA–protein complex. This results in a new hydrophobic core, an intraprotein hydrogen bond and a quadruple stacking interaction between U1A and U1hpII. Here, we used a surface plasmon resonance-based biosensor to gain mechanistic insight into the role of helix C in mediating the interaction with U1hpII. Truncation, removal or disruption of the helix exposes the RNA-binding surface, resulting in an increase in the association rate, while simultaneously reducing the ability of the complex to lock, reflected in a loss of complex stability. Disruption of the quadruple stacking interaction has minor kinetic effects when compared with removal of the intraprotein hydrogen bonds. These data provide new insights into the mechanism whereby sequences C-terminal to an RRM can influence RNA binding.

Abstract 4136: Development of a new and sensitive detection technology for galectin cancer proteins.

Abstract The galectin protein family consists of fifteen galactoside-binding proteins that are present in all classes of life where they function as cell-cell and cell-matrix interaction mediators. Galectins are however also highly overexpressed in various processes related to cancer, including apoptosis, angiogenesis and metastasis. Galectins are therefore excellent targets for tumor diagnostics and medical prognostic purposes. Current proteomic tools, e.g. Polymerase Chain Reaction (PCR) and Enzyme-linked Immunosorbent Assay (ELISA), are based on protein abundance rather than protein activity. In contrast, we have developed a galectin detection assay that visualizes galactoside-binding, i.e. functional, galectins using PamChip® microarray technology. Firstly, antibodies directed against different galectins are efficiently immobilized on the microarray surface by the Fc-binding protein A/G. Then galectin-1 was captured from a spiked cell lysate that is added to the microarray and the unbound proteins are washed away. The galectin presence is subsequently quantified with a general fluorescent ligand that is only bound by active galectins. Several ligands based on lactose and lactosamine were designed and tested. With the best ligands it was possible to detect galectin quantities in the low nanogram range using only 1 μg or less of precious anti-galectin antibodies per measurement. These results are truly promising for the use of the newly developed galectin detection technology in a clinical setting. Citation Format: Hilde van Hattum, Rob Ruijtenbeek, Riet Hilhorst, Roland Pieters. Development of a new and sensitive detection technology for galectin cancer proteins. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4136. doi:10.1158/1538-7445.AM2013-4136

Rice Os9BGlu31 Is a Transglucosidase with the Capacity to Equilibrate Phenylpropanoid, Flavonoid, and Phytohormone Glycoconjugates

Glycosylation is an important mechanism of controlling the reactivities and bioactivities of plant secondary metabolites and phytohormones. Rice (Oryza sativa) Os9BGlu31 is a glycoside hydrolase family GH1 transglycosidase that acts to transfer glucose between phenolic acids, phytohormones, and flavonoids. The highest activity was observed with the donors feruloyl-glucose, 4-coumaroyl-glucose, and sinapoyl-glucose, which are known to serve as donors in acyl and glucosyl transfer reactions in the vacuole, where Os9BGlu31 is localized. The free acids of these compounds also served as the best acceptors, suggesting that Os9BGlu31 may equilibrate the levels of phenolic acids and carboxylated phytohormones and their glucoconjugates. The Os9BGlu31 gene is most highly expressed in senescing flag leaf and developing seed and is induced in rice seedlings in response to drought stress and treatment with phytohormones, including abscisic acid, ethephon, methyljasmonate, 2,4-dichlorophenoxyacetic acid, and kinetin. Although site-directed mutagenesis of Os9BGlu31 indicated a function for the putative catalytic acid/base (Glu(169)), catalytic nucleophile residues (Glu(387)), and His(386), the wild type enzyme displays an unusual lack of inhibition by mechanism-based inhibitors of GH1 β-glucosidases that utilize a double displacement retaining mechanism.