Architecture of the Sema3A/PlexinA4/Neuropilin tripartite complex

Secreted class 3 semaphorins (Sema3s) form tripartite complexes with the plexin receptor and neuropilin coreceptor, which are both transmembrane proteins that together mediate semaphorin signal for neuronal axon guidance and other processes. Despite extensive investigations, the overall architecture of and the molecular interactions in the Sema3/plexin/neuropilin complex are incompletely understood. Here we present the cryo-EM structure of a near intact extracellular region complex of Sema3A, PlexinA4 and Neuropilin 1 (Nrp1) at 3.7 Å resolution. The structure shows a large symmetric 2:2:2 assembly in which each subunit makes multiple interactions with others. The two PlexinA4 molecules in the complex do not interact directly, but their membrane proximal regions are close to each other and poised to promote the formation of the intracellular active dimer for signaling. The structure reveals a previously unknown interface between the a2b1b2 module in Nrp1 and the Sema domain of Sema3A. This interaction places the a2b1b2 module at the top of the complex, far away from the plasma membrane where the transmembrane regions of Nrp1 and PlexinA4 embed. As a result, the region following the a2b1b2 module in Nrp1 must span a large distance to allow the connection to the transmembrane region, suggesting an essential role for the long non-conserved linkers and the MAM domain in neuropilin in the semaphorin/plexin/neuropilin complex.

Generation of novel trimeric fragments of human SP-A and SP-D after recombinant soluble expression in E. coli

Surfactant treatment for neonatal respiratory distress syndrome has dramatically improved survival of preterm infants. However, this has resulted in a markedly increased incidence of sequelae such as neonatal chronic inflammatory lung disease. The current surfactant preparations in clinical use lack the natural lung defence proteins surfactant proteins (SP)-A and D. These are known to have anti-inflammatory and anti-infective properties essential for maintaining healthy non-inflamed lungs.

Supplementation of currently available animal derived surfactant therapeutics with these anti-inflammatory proteins in the first few days of life could prevent the development of inflammatory lung disease in premature babies. However, current systems for production of recombinant versions of SP-A and SP-D require a complex solubilisation and refolding protocol limiting expression at scale for drug development.

Using a novel solubility tag, we describe the expression and purification of recombinant fragments of human (rfh) SP-A and SP-D using Escherichia coli without the need for refolding. We obtained a mean (± SD) of 23.3 (± 5.4) mg and 86 mg (± 3.5) per litre yield of rfhSP-A and rfhSP-D, respectively. rfhSP-D was trimeric and 68% bound to a ManNAc-affinity column, giving a final yield of 57.5 mg/litre of highly pure protein, substantially higher than the 3.3 mg/litre obtained through the standard refolding protocol. Further optimisation of this novel lab based method could potentially make rfhSP-A and rfhSP-D production more commercially feasible to enable development of novel therapeutics for the treatment of lung infection and inflammation.

Identification of midgut membrane proteins from different instars of Helicoverpa armigera (Lepidoptera: Noctuidae) that bind to Cry1Ac toxin

Helicoverpa armigera is a polyphagous pest sensitive to Cry1Ac protein from Bacillus thuringiensis (Bt). The susceptibility of the different larval instars of H. armigera to Cry1Ac protoxin showed a significant 45-fold reduction in late instars compared to early instars. A possible hypothesis is that gut surface proteins that bind to Cry1Ac differ in both instars, although higher Cry toxin degradation in late instars could also explain the observed differences in susceptibility. Here we compared the Cry1Ac-binding proteins from second and fifth instars by pull-down assays and liquid chromatography coupled to mass spectrometry analysis (LC-MS/MS). The data show differential protein interaction patterns of Cry1Ac in the two instars analyzed. Alkaline phosphatase, and other membrane proteins, such as prohibitin and an anion selective channel protein were identified only in the second instar, suggesting that these proteins may be involved in the higher toxicity of Cry1Ac in early instars of H. armigera. Eleven Cry1Ac binindg proteins were identified exclusively in late instar larvae, like different proteases such as trypsin-like protease, azurocidin-like proteinase, and carboxypeptidase. Different aminopeptidase N isofroms were identified in both instar larvae. We compared the Cry1Ac protoxin degradation using midgut juice from late and early instars, showing that the midgut juice from late instars is more efficient to degrade Cry1Ac protoxin than that of early instars, suggesting that increased proteolytic activity on the toxin could also explain the low Cry1Ac toxicity in late instars.

Identification of Aminopeptidase-N2 as a Cry2Ab binding protein in Manduca sexta

Bacillus thuringiensis Cry2Ab toxin has been used in combination with Cry1Ac for resistance management on the Bt-cotton that is widely planted worldwide. However, little is known regarding Cry2Ab mode of action. Particularly, there is a gap of knowledge on the identification of insect midgut proteins that bind Cry2Ab and mediate toxicity. In the case of Cry1Ab toxin, a transmembrane cadherin protein and glycosyl-phosphatidylinositol (GPI) anchored proteins like aminopeptidase-N1 (APN1) or alkaline-phosphatase (ALP) from Manduca sexta, have been shown to be important for oligomer formation and insertion into the membrane. Binding competition experiments showed that Cry2Ab toxin does not share binding sites with Cry1Ab toxin in M. sexta brush border membrane vesicles (BBMV). Also, that Cry2Ab shows reduced binding to the Cry1Ab binding molecules cadherin, APN1 or ALP. Finally, ligand blot experiments and protein sequence by LC-MS/MS identified APN2 isoform as a Cry2Ab binding protein. Cloning and expression of APN2 confirmed that APN2 is a Cry2Ab binding protein.

Purification of Plant Receptor Kinases from Plant Plasma Membranes

Receptor kinases play a central role in various biological processes, but due to their low abundance and highly hydrophobic and dynamic nature, only a few of them have been functionally characterized, and their partners and ligands remain unidentified. Receptor protein extraction and purification from plant tissues is one of the most challenging steps for the success of various biochemical analyses to characterize their function. Immunoprecipitation is a widely used and selective method for enriching or purifying a specific protein. Here we describe two different optimized protein purification protocols, batch and on-chip immunoprecipitation, which efficiently isolate plant membrane receptor kinases for functional analysis.

Fate of insecticidal Bacillus thuringiensis Cry protein in soil: differences between purified toxin and biopesticide formulation

BACKGROUND

Bacillus thuringiensis produces insecticidal proteins known as Cry, and its efficiency and absence of side effects make it the most widely used biopesticide. There is little information on the role of soils in the fate of Cry proteins from commercial biopesticide formulations, unlike toxins from genetically modified crops, which have been intensively studied in recent years. The persistence of Cry in soil was followed under field and laboratory conditions.

RESULTS

Sunlight accelerated loss of detectable Cry under laboratory conditions, but little effect of shade was observed under field conditions. The half-life of biopesticide proteins in soil under natural conditions was about 1 week. Strong temperature effects were observed, but they differed for biopesticide and purified protein, indicating different limiting steps.

CONCLUSION

For the biopesticide, the observed decline in detectable protein was due to biological factors, possibly including the germination of B. thuringiensis spores, and was favoured by higher temperature. In contrast, for purified proteins, the decline in detectable protein was slower at low temperature, probably because the conformational changes of the soil-adsorbed protein, which cause fixation and hence reduced extraction efficiency, are temperature dependent. © 2016 Society of Chemical Industry.

Analysis of the carbohydrate-binding-module from Fragaria x ananassa α-L-arabinofuranosidase 1

α-L-arabinofuranosidases (EC 3.2.1.55) are enzymes involved in the catabolism of several cell-wall polysaccharides such as pectins and hemicelluloses, catalyzing the hydrolysis of terminal non-reducing α-L-arabinofuranosil residues. Bioinformatic analysis of the aminoacidic sequences of Fragaria x ananassa α-L-arabinofuranosidases predict a putative carbohydrate-binding-module of the family CBM_4_9, associated to a wide range of carbohydrate affinities. In this study, we report the characterization of the binding affinity profile to different cell wall polysaccharides of the putative CBM of α-L-arabinofuranosidase 1 from Fragaria x ananassa (CBM-FaARA1). The sequence encoding for the putative CBM was cloned and expressed in Escherichia coli, and the resultant recombinant protein was purified from inclusion bodies by a Nickel affinity chromatography under denaturing conditions. The refolded recombinant protein was then subjected to binding assays and affinity gel electrophoresis, which indicated its ability to bind cellulose and also high affinity for homogalacturonans.

A Rapid Method for Refolding Cell Surface Receptors and Ligands

Production of membrane-associated cell surface receptors and their ligands is often a cumbersome, expensive, and time-consuming process that limits detailed structural and functional characterization of this important class of proteins. Here we report a rapid method for refolding inclusion-body-based, recombinant cell surface receptors and ligands in one day, a speed equivalent to that of soluble protein production. This method efficiently couples modular on-column immobilized metal ion affinity purification and solid-phase protein refolding. We demonstrated the general utility of this method for producing multiple functionally active immunoreceptors, ligands, and viral decoys, including challenging cell surface proteins that cannot be produced using typical dialysis- or dilution-based refolding approaches.

Streptococcal Infection-related Nephritis (SIRN) Manifesting Membranoproliferative Glomerulonephritis Type I

We herein report the case of an 18-year-old boy who developed nephrotic syndrome and hypertension after upper airway inflammation. Post-streptococcal acute glomerulonephritis was diagnosed on the basis of a high antistreptolysin O titer, hypocomplementemia, proteinuria, and microscopic hematuria. A renal biopsy was performed due to persistent proteinuria, and the pathological diagnosis was membranoproliferative glomerulonephritis (MPGN) type I. Glomeruli showed positive staining for nephritis-associated plasmin receptor (NAPlr), a nephritogenic group A streptococcal antigen, and plasmin activity was found in a similar distribution as NAPlr deposition. This rare case of streptococcal infection-related nephritis (SIRN) manifesting MPGN type I supports the histological diversity of SIRN.

Production of recombinant PvDBPII, receptor binding domain of Plasmodium vivax Duffy binding protein, and evaluation of immunogenicity to identify an adjuvant formulation for vaccine development

Plasmodium vivax is dependent on interaction with the Duffy antigen receptor for chemokines (DARC) for invasion of human erythrocytes. The P. vivax Duffy binding protein (PvDBP) mediates interaction of P. vivax merozoites with DARC. The DARC receptor-binding domain lies in a conserved N-terminal cysteine-rich region of PvDBP referred to as region II (PvDBPII). PvDBPII is an attractive vaccine candidate since antibodies raised against PvDBPII block erythrocyte invasion by P. vivax. Here, we describe methods to produce recombinant PvDBPII in its correctly folded conformation. A synthetic gene optimized for expression of PvDBPII in Escherichia coli and fed batch fermentation process based on exponential feeding strategy was used to achieve high levels of expression of recombinant PvDBPII. Recombinant PvDBPII was isolated from inclusion bodies, refolded by rapid dilution and purified by ion exchange chromatography. Purified recombinant PvDBPII was characterized for identity, purity and functional activity using standardized release assays. Recombinant PvDBPII formulated with various human compatible adjuvants including glycosylpyranosyl lipid A-stable emulsion (GLA-SE) and alhydrogel was used for immunogenicity studies in small animals to downselect a suitable formulation for clinical development. Sera collected from immunized animals were tested for recognition of PvDBPII and inhibition of PvDBPII-DARC binding. GLA-SE formulations of PvDBPII yielded higher ELISA and binding inhibition titres compared to PvDBPII formulated with alhydrogel. These data support further development of a recombinant vaccine for P. vivax based on PvDBPII formulated with GLA-SE.

Two nucleoside receptors from Streptomyces coelicolor: expression of the genes and characterization of the recombinant proteins

Streptomyces coelicolor is a soil-dwelling bacterium that undergoes an intricate, saprophytic lifecycle. The bacterium takes up exogenous nucleosides for nucleic acid synthesis or use as carbon and energy sources. However, nucleosides must pass through the membrane with the help of transporters. In the present work, the SCO4884 and SCO4885 genes were cloned into pCOLADuet-1 and overexpressed in Escherichia coli BL21. Each protein was monomeric. Using isothermal titration calorimetry, we determined that SCO4884 and SCO4885 are likely nucleoside receptors with affinity for adenosine and pyrimidine nucleosides. On the basis of bioinformatics analysis and the transporter classification system, we speculate that SCO4884-SCO4888 is an ABC-like transporter responsible for the uptake of adenosine and pyrimidine nucleosides.

Kallikrein-related peptidases in cancers of gastrointestinal tract: an inside view of their role and clinical significance

Human tissue kallikrein (KLK1) and is related peptidases (KLK2-KLK15) are a family of 15 homologous serine proteases, participating in numerous processes of normal physiology. Considering the irreversible impact of proteases on substrates, the tissue-dependent regulation of KLKs activity becomes crucial for their beneficial role in normal homeostasis. Moreover, KLKs expression is strongly regulated at the transcriptional and post-transcriptional level by steroid hormones and miRNAs, respectively. Deregulation of KLKs expression, secretion and/or activation has been observed in most human malignancies and there is a trend to identify their role in the multi-complex process of cancer development. The identification of extracellular matrix (ECM) proteins, cell-surface receptors, cell-surface adhesion molecules and growth factors among substrates, clearly support the driving role of KLK abnormal expression and function during tumorigenesis and cancer progression. KLKs have also clinical utility in cancer diagnosis and monitoring like KLK 3 (PSA) in prostate cancer. In this review, we tried to summarize the existing literature about the role of KLKs in gastrointestinal cancers as well as to emphasize their clinical significance for patients' prognosis.

Molecular characterization of the vitellogenin receptor from the tick, Amblyomma hebraeum (Acari: Ixodidae)

We have identified the full-length cDNA encoding a vitellogenin receptor (VgR) from the African bont tick Amblyomma hebraeum Koch (1844). VgRs are members of the low-density lipoprotein receptor superfamily that promote the uptake of the yolk protein vitellogenin (Vg), from the haemolymph. The AhVgR (GenBank accession No. JX846592) is 5703 bp, and encodes an 1801 aa protein with a 196.5 kDa molecular mass following cleavage of a 22 aa signal peptide. Phylogenetic analysis indicates that AhVgR is highly similar to other tick VgRs. AhVgR is expressed in only the ovary of mated, engorged females, and is absent in all other female tissues and in both fed and unfed males. Unfed, adult females injected with a VgR-dsRNA probe to knock-down VgR expression experienced a significant delay in ovary development and started oviposition significantly later than controls. These results indicate that the expression of AhVgR is important for the uptake of Vg and subsequent maturation of the oocytes.

Cloning, overexpression, purification and preliminary X-ray analysis of the catalytic domain of the ethylene receptor ETR1 from Arabidopsis thaliana

Ethylene is a gaseous plant hormone which controls many aspects of plant growth and development. It is perceived by membrane-bound receptors with a similarity to bacterial two-component systems. The catalytic and ATP-binding domain of the histidine kinase domain of ETR1 from Arabidopsis thaliana has been cloned, overexpressed and crystallized. The protein was crystallized together with various nucleotides. Crystals obtained in the presence of ADP belonged to space group I222 or I2(1)2(1)2(1) with one molecule per asymmetric unit. They diffracted X-ray radiation to beyond 1.85 Å resolution.

Bioactive hyaluronan fragment (hexasaccharide) detects specific hexa-binding proteins in human breast and stomach cancer: possible role in tumorogenesis

Hyaluronan (HA) is a component of extracellular matrix that influences cell-proliferation, migration, development, regeneration, normal tissue remodeling, tissues undergoing malignancy and tumor cell interaction. The widespread occurrence of HA binding proteins, their involvement in tissue organization and the control of cellular behavior are well documented. The low molecular mass HA fragments can also induce a variety of biological events, including chemokine gene expression, transcription factor expression and angiogenesis. It is believed that these fragments are more potent in cellular activities than high molecular mass HA. In this study, we isolated the various fragments by gel permeation chromatography of hyaluronidase digested HA and characterized by fluoro assisted carbohydrate electrophoresis (FACE) and matrix assisted laser desorption ionization analysis (MALDI). Detection and distribution of cellular receptors in invasive tumor tissues for HA polymer and HA fragments were determined both by Western blot and histochemistry. The study demonstrated the overexpression of HA-hexa binding protein in human tumors of breast and stomach and its involvement in tumorogenesis.

One-step immunopurification and lectinochemical characterization of the Duffy atypical chemokine receptor from human erythrocytes

Duffy antigen/receptor for chemokines (DARC) is a glycosylated seven-transmembrane protein acting as a blood group antigen, a chemokine binding protein and a receptor for Plasmodium vivax malaria parasite. It is present on erythrocytes and endothelial cells of postcapillary venules. The N-terminal extracellular domain of the Duffy glycoprotein carries Fy(a)/Fy(b) blood group antigens and Fy6 linear epitope recognized by monoclonal antibodies. Previously, we have shown that recombinant Duffy protein expressed in K562 cells has three N-linked oligosaccharide chains, which are mainly of complex-type. Here we report a one-step purification method of Duffy protein from human erythrocytes. DARC was extracted from erythrocyte membranes in the presence of 1% n-dodecyl-β-D-maltoside (DDM) and 0.05% cholesteryl hemisuccinate (CHS) and purified by affinity chromatography using immobilized anti-Fy6 2C3 mouse monoclonal antibody. Duffy glycoprotein was eluted from the column with synthetic DFEDVWN peptide containing epitope for 2C3 monoclonal antibody. In this single-step immunoaffinity purification method we obtained highly purified DARC, which migrates in SDS-polyacrylamide gel as a major diffuse band corresponding to a molecular mass of 40-47 kDa. In ELISA purified Duffy glycoprotein binds anti-Duffy antibodies recognizing epitopes located on distinct regions of the molecule. Results of circular dichroism measurement indicate that purified DARC has a high content of α-helical secondary structure typical for chemokine receptors. Analysis of DARC glycans performed by means of lectin blotting and glycosidase digestion suggests that native Duffy N-glycans are mostly triantennary complex-type, terminated with α2-3- and α2-6-linked sialic acid residues with bisecting GlcNAc and α1-6-linked fucose at the core.

Novel transmembrane receptor involved in phagosome transport of lysozymes and β-hexosaminidase in the enteric protozoan Entamoeba histolytica

Lysozymes and hexosaminidases are ubiquitous hydrolases in bacteria and eukaryotes. In phagocytic lower eukaryotes and professional phagocytes from higher eukaryotes, they are involved in the degradation of ingested bacteria in phagosomes. In Entamoeba histolytica, which is the intestinal protozoan parasite that causes amoebiasis, phagocytosis plays a pivotal role in the nutrient acquisition and the evasion from the host defense systems. While the content of phagosomes and biochemical and physiological roles of the major phagosomal proteins have been established in E. histolytica, the mechanisms of trafficking of these phagosomal proteins, in general, remain largely unknown. In this study, we identified and characterized for the first time the putative receptor/carrier involved in the transport of the above-mentioned hydrolases to phagosomes. We have shown that the receptor, designated as cysteine protease binding protein family 8 (CPBF8), is localized in lysosomes and mediates transport of lysozymes and β-hexosaminidase α-subunit to phagosomes when the amoeba ingests mammalian cells or Gram-positive bacillus Clostridium perfringens. We have also shown that the binding of CPBF8 to the cargos is mediated by the serine-rich domain, more specifically three serine residues of the domain, which likely contains trifluoroacetic acid-sensitive O-phosphodiester-linked glycan modifications, of CPBF8. We further showed that the repression of CPBF8 by gene silencing reduced the lysozyme and β-hexosaminidase activity in phagosomes and delayed the degradation of C. perfringens. Repression of CPBF8 also resulted in decrease in the cytopathy against the mammalian cells, suggesting that CPBF8 may also be involved in, besides the degradation of ingested bacteria, the pathogenesis against the mammalian hosts. This work represents the first case of the identification of a transport receptor of hydrolytic enzymes responsible for the degradation of microorganisms in phagosomes.

Phagocytosis is the cellular process of engulfing solid particles to form an internal phagosome in protozoa, algae, and professional phagocytes of multicellular eukaryotic organisms. In phagocytic protozoa, phagocytosis is involved in the acquisition of nutrients, and the evasion from the host immune system and inflammation. While hydrolytic enzymes that are essential for the efficient and regulated degradation of phagocytosed particles, such as bacteria, fungi, and eukaryotic organisms, have been characterized, the mechanisms of the transport of these proteins are poorly understood. In the present study, we have demonstrated, for the first time, the molecular mechanisms of how the digestive enzymes are transported to phagosomes. Understanding of such mechanisms of the transport of phagosomal proteins at the molecular level may lead to the identification of a novel target for the development of new preventive measures against parasitic infections caused by phagocytic protozoa.

Simplified evaluation of apoptosis using the Muse cell analyzer

The degree of apoptosis in a cell population is an important parameter of cell health and is characterized by distinct morphological changes. Current methods of accurate detection and measurement of cellular apoptosis require expensive and complicated instrument platforms and expertise. The Muse Cell Analyzer is a unique instrument that enables multidimensional cell health analysis on a single platform. In this study, we used the Muse Cell Analyzer for apoptosis studies using the Muse Annexin V & Dead Cell Assay. The assay is based on the detection of phosphatidylserine (PS) on the surface of apoptotic cells. The results obtained from Muse Cell Analyzer were compared with traditional methods for apoptosis analysis. Our results indicate that Muse Annexin V & Dead Cell Assay and software module enabled the acquisition of accurate and highly precise measurements of cellular apoptosis. The assay is versatile and works with both suspension and adherent cell lines and multiple treatment conditions.

[The efficacy of enhancing murine zona pellucid 3 DNA vaccine immunized through intranasal vaccination by IL-15]

AIM

To observe the efficacy of enhancing murine zona pellucid 3(mZP3) DNA vaccine immunized through intranasal vaccination by IL-15 as adjuvant and chitosan as delivery vactor.

METHODS

C57BL/6 mice were delivered with chitosan-loaded mZP3 DNA vaccine or IL-15+pcD-mZP3 vaccine by intranasal route, and to detect specific IgG in serum and sIgA in vaginal fluid by indirect ELISA, and to perform fertility experiment that all female C57BL/6 mice were mated(one male for each female) with normal males of similar age. To do histology analysis of immunized mice ovary and lungs for morphology of ovary.

RESULTS

The results of ELISA showed IL-15 can promote IgG antibody level of immunized mice, and the fertility rate was decreased to some degrees.

CONCLUSION

IL-15 and chitosan can enhance the antibody levels induced by mZP3 DNA vaccine, and reduce murine fertility rate to a certain extent.

A comprehensive assessment of the effects of Bt cotton on Coleomegilla maculata demonstrates no detrimental effects by Cry1Ac and Cry2Ab

The ladybird beetle, Coleomegilla maculata (DeGeer), is a common and abundant predator in many cropping systems. Its larvae and adults are predaceous, feeding on aphids, thrips, lepidopteran larvae and plant tissues, such as pollen. Therefore, this species is exposed to insecticidal proteins expressed in insect-resistant, genetically engineered cotton expressing Cry proteins derived from Bacillus thuringiensis (Bt). A tritrophic bioassay was conduced to evaluate the potential impact of Cry2Ab- and Cry1Ac-expressing cotton on fitness parameters of C. maculata using Bt-susceptible and -resistant larvae of Trichoplusia ni as prey. Coleomegilla maculata survival, development time, adult weight and fecundity were not different when they were fed with resistant T. ni larvae reared on either Bt or control cotton. To ensure that C. maculata were not sensitive to the tested Cry toxins independent from the plant background and to add certainty to the hazard assessment, C. maculata larvae were fed artificial diet incorporated with Cry2Ab, Cry1Ac or both at >10 times higher concentrations than in cotton tissue. Artificial diet containing E-64 was included as a positive control. No differences were detected in any life-table parameters between Cry protein-containing diet treatments and the control diet. In contrast, larvae of C. maculata fed the E-64 could not develop to the pupal stage and the 7-d larval weight was significantly negatively affected. In both feeding assays, the stability and bioactivity of Cry proteins in the food sources were confirmed by ELISA and sensitive-insect bioassays. Our results show that C. maculata is not affected by Bt cotton and is not sensitive to Cry2Ab and Cry1Ac at concentrations exceeding the levels in Bt cotton, thus demonstrating that Bt cotton will pose a negligible risk to C. maculata. More importantly, this study demonstrates a comprehensive system for assessing the risk of genetically modified plants on non-target organisms.

Synthesis and application of an N-acylated l-homoserine lactone derivatized affinity matrix for the isolation of quorum sensing signal receptors

The design and synthesis of an agarose resin functionalized with a Gram-negative quorum sensing (QS) signaling molecule analogue is described. The modified resin was utilized in affinity pull-down assays to successfully isolate QscR, a LuxR-type QS receptor from Pseudomonas aeruginosa. This resin may facilitate the identification of novel QS signal receptors using affinity chromatography techniques.

Drosophila photoreceptor cells exploited for the production of eukaryotic membrane proteins: receptors, transporters and channels

BACKGROUND

Membrane proteins (MPs) play key roles in signal transduction. However, understanding their function at a molecular level is mostly hampered by the lack of protein in suitable amount and quality. Despite impressive developments in the expression of prokaryotic MPs, eukaryotic MP production has lagged behind and there is a need for new expression strategies. In a pilot study, we produced a Drosophila glutamate receptor specifically in the eyes of transgenic flies, exploiting the naturally abundant membrane stacks in the photoreceptor cells (PRCs). Now we address the question whether the PRCs also process different classes of medically relevant target MPs which were so far notoriously difficult to handle with conventional expression strategies.

PRINCIPAL FINDINGS

We describe the homologous and heterologous expression of 10 different targets from the three major MP classes--G protein-coupled receptors (GPCRs), transporters and channels in Drosophila eyes. PRCs offered an extraordinary capacity to produce, fold and accommodate massive amounts of MPs. The expression of some MPs reached similar levels as the endogenous rhodopsin, indicating that the PRC membranes were almost unsaturable. Expression of endogenous rhodopsin was not affected by the target MPs and both could coexist in the membrane stacks. Heterologous expression levels reached about 270 to 500 pmol/mg total MP, resulting in 0.2-0.4 mg purified target MP from 1 g of fly heads. The metabotropic glutamate receptor and human serotonin transporter--both involved in synaptic transmission--showed native pharmacological characteristics and could be purified to homogeneity as a prerequisite for further studies.

SIGNIFICANCE

We demonstrate expression in Drosophila PRCs as an efficient and inexpensive tool for the large scale production of functional eukaryotic MPs. The fly eye system offers a number of advantages over conventional expression systems and paves the way for in-depth analyses of eukaryotic MPs that have so far not been accessible to biochemical and biophysical studies.

[Preparation and characterization of a polyclonal antibody against human Fibrocystin-L]

AIM

PKHDL1 (the gene for Polycystic Kidney and Hepatic Disease Like-1) had been recently identified, but characteristics of the gene product, Fibrocystin-L (FPC-L), still remain unknown. We therefore produced a rabbit polyclonal antibody hFL-Np to explore the cellular characteristics of this novel protein.

METHODS

Based on the hydrophobic/hydrophilic analyses, chose a cDNA fragment which encodes 633L-768K amino acids of the FPC-L and amplified it by RT-PCR. The PCR product was then cloned into a prokaryotic expression vector pGEX-GST. With IPTG induction, the antigen hFL-N was produced and further purified. A rabbit was immunized with the antigen and its antiserum was collected. Applied Western blot with the polyclonal antiserum hFL-Np and validated the antibody specific for FPC-L protein. In addition, also used immunofluorescence staining with hFL-Np to detect the subcellular distribution in cultured HEK293 cells.

RESULTS

The prokaryotic expression vector pGEX-hFL-N was successfully constructed and a hFL-N antigen was produced in E.coli Rossetta cells. Using the antigen, a polyclonal antibody hFL-Np was produced and the specificity for FPC-L was also proved by biochemistry and cellular assays. Using the antibody, the cellular staining reveals that FPC-L was a cytosolic protein.

CONCLUSION

We produced an anti-FPC-L polyclonal antibody hFL-Np. By biochemistry and cellular characterization, proved that the polyclonal antibody hFL-Np is specific for FPC-L and demonstrated FPC-L is a cytosolic protein. The finding provides a platform for further dissecting FPC-L functions in mammalian development.

Characterization of receptor proteins using affinity cross-linking with biotinylated ligands

The plant genome encodes a wide range of receptor-like proteins but the function of most of these proteins is unknown. We propose the use of affinity cross-linking of biotinylated ligands for a ligand-based survey of the corresponding receptor molecules. Biotinylated ligands not only enable the analysis of receptor-ligand interactions without the use of radioactive compounds but also the isolation and identification of receptor molecules by a simple affinity trapping method. We successfully applied this method for the characterization, isolation and identification of the chitin elicitor binding protein (CEBiP). A biocytin hydrazide conjugate of N-acetylchitooctaose (GN8-Bio) was synthesized and used for the detection of CEBiP in the plasma or microsomal membrane preparations from rice and carrot cells. Binding characteristics of CEBiP analyzed by inhibition studies were in good agreement with the previous results obtained with the use of a radiolabeled ligand. The biotin-tagged CEBiP could be purified by avidin affinity chromatography and identified by LC-MALDI-MS/MS after tryptic digestion. We also used this method to detect OsFLS2, a rice receptor-like kinase for the perception of the peptide elicitor flg22, in membrane preparations from rice cells overexpressing OsFLS2. This work demonstrates the applicability of this method to the purification and identification of plant receptor proteins.

Heterologous expression of human membrane receptors in the yeast Saccharomyces cerevisiae

Due to their implication in numerous diseases like cancer, cystic fibrosis, epilepsy, hyperinsulinism, heart failure, hypertension, and Alzheimer disease, membrane proteins (MPs) represent around 50% of drug targets. However, only 204 crystal structures of MPs have been solved. Structural analysis requires large quantities of pure and active proteins. The majority of medically and pharmaceutically relevant MPs are present in tissues at low concentration, which makes heterologous expression in large-scale production-adapted cells a prerequisite for structural studies. The yeast Saccharomyces cerevisiae is a convenient host for the production of mammalian MPs for functional and structural studies. Like bacteria, they are straightforward to manipulate genetically, are well characterized, can be easily cultured, and can be grown inexpensively in large quantities. The advantage of yeast compared to bacteria is that they have protein-processing and posttranslational modification mechanisms related to those found in mammalian cells. The recombinant rabbit muscle Ca(2+)-ATPase (adenosine triphosphatase), the first heterologously expressed mammalian MP for which the crystal structure was resolved, has been produced in S. cerevisiae. In this chapter, the focus is on expression of recombinant human integral MPs in a functional state at the plasma membrane of the yeast S. cerevisiae. Optimization of yeast culture and of MP preparations is detailed for two human receptors of the Hedgehog pathway: Patched and Smoothened.

Using RNA aptamers and the proximity ligation assay for the detection of cell surface antigens

The detection and typing of tumor cells based on differentially or similarly expressed antigens (biomarkers) have proven to be increasingly important for the diagnosis and treatment of various cancers. Sensitive techniques for the detection of cell surface antigens are therefore crucial for the early and accurate detection of cancer. Although techniques such as ELISA and tissue staining have proven their worth, these techniques often either require substantial amounts of starting material or are prone to high background and false negatives. The proximity ligation assay (PLA) has proven to be an exquisitely sensitive technique with very low background. Two probes that bind adjacent to one another on a protein target can be ligated, yielding a unique amplicon that can be sensitively detected by real-time PCR. We have now adapted PLA to cell surface protein targets using modified RNA aptamers, and have shown that aptamer-based cell surface PLA can successfully detect and differentiate between cells that differentially express a tumor antigen, the prostate specific membrane antigen (PSMA).

Antibody affinity optimization using yeast cell surface display

Many biosensors depend on molecular recognition reagents to achieve highly sensitive and specific detection levels of an analyte of interest. Although new and improved detection platforms continue to be developed, improvements in the affinity and specificity of the molecular recognition reagents often dictate the ultimate performance level and utility of the instrument. Accordingly, large effort is placed in discovering and characterizing the reagents to be used for a biosensor application. Antibodies, owing to their unparalleled ability to bind a diverse array of antigens with high affinity and specificity, have been widely used as molecular recognition reagents in the biosensor field. The recent advent of recombinant in vitro antibody display technologies, in general, and yeast surface display, in particular, allow specific traits of a given antibody to be discreetly augmented to enhance biosensor performance. Large variegated libraries derived from existing antibodies already employed in a particular biosensor can be created and screened for mutations that confer a desired improved phenotype leading to enhanced biosensor performance. This chapter will provide a protocol for the affinity maturation of a previously isolated monoclonal antibody, the most widely used application of in vitro directed evolution.

Candidates for membrane progestin receptors--past approaches and future challenges

Progestins have a broad range of functions in reproductive biology. Many rapid nongenomic actions of progestins have been identified, including induction of oocyte maturation, modulation of reproductive signaling in the brain, rapid activation of breast cancer cell signaling, induction of the acrosomal reaction and hypermotility in mammalian sperm. Currently, there are three receptor candidates for mediating rapid progestin actions: (1) membrane progestin receptors (mPRs); (2) progestin receptor membrane components (PGRMCs); and (3) nuclear progestin receptors (nPRs). The recently-described mPR family of proteins has seven integral transmembrane domains and mediates signaling via G-protein coupled pathways. The PGRMCs have a single transmembrane with putative Src homology domains for potential activation of second messengers. The classical nPRs, in addition to having well defined transcriptional activity, can also mediate rapid activation of intracellular signaling pathways. However, details of the mechanisms by which these three classes of progestin receptors mediate rapid intracellular signaling and their subcellular localization remain unclear. In addition, mPRs, nPRs and PGRMCs exhibit overlapping expression and functions in multiple tissues, implying potential interactions during oocyte maturation, parturition, and breast cancer signaling in individual cells. However, the overwhelming majority of studies to date have focused on the functions of one of these groups of receptors in isolation. This review will summarize recent findings on the three major progestin receptor candidates, emphasizing the different approaches used, some experimental pitfalls, and current controversies. We will also review evidence for the involvement of mPRs and nPRs in one of the most well-characterized nongenomic steroid actions in basal vertebrates, oocyte maturation, and conclude by suggesting some future areas of research. Clarification of the controversies surrounding the identities and localization of membrane progestin receptors may help direct future research that could advance our understanding of rapid actions of steroids.

Regulation and characterization of Thermobifida fusca carbohydrate-binding module proteins E7 and E8

E7, a single domain Family 33 cellulose binding module (CBM) protein, and E8, a non-catalytic, three-domain protein consisting of a Family 33 CBM, a FNIII domain, followed by a Family 2 CBM, were cloned, expressed, purified, and characterized. Western blots showed that E7 and E8 were induced and secreted when Thermobifida fusca was grown on cellobiose, Solka floc, switchgrass, or alfalfa as well as on beta-1,3 linked glucose molecules such as laminaribiose or pachyman. E8 bound well to alpha- and beta-chitin and bacterial microcrystalline cellulose (BMCC) at all pHs tested. E7 bound strongly to beta-chitin, less well to alpha-chitin and more weakly to BMCC than E8. Filter paper binding assays showed that E7 was 28% bound, E8 was 39% bound, a purified CBM2 binding domain from Cel6B was 88% bound, and only 5% of the Cel5A catalytic domain was bound. A C-terminal 6xHis tag influenced binding of both E7 and E8 to these substrates. Filter paper activity assays showed enhanced activity of T. fusca cellulases when E7 or E8 was present. This effect was observed at very low concentrations of cellulases or at very long times into the reaction and was mainly independent of the type of cellulase and the number of cellulases in the mixture. E8, and to a lesser extent E7, significantly enhanced the activity of Serratia marscescens Chitinase C on beta-chitin.

Immunoglobulin-like transcript 3-Fc suppresses T-cell responses to allogeneic human islet transplants in hu-NOD/SCID mice

OBJECTIVE

The aim of our study was to explore the immunomodulatory activity of soluble immunoglobulin (Ig)-like transcript (ILT) 3-Fc in pancreatic islet transplantation and to determine its mechanism of action.

RESEARCH DESIGN AND METHODS

NOD/SCID mice in which diabetes was induced by streptozotocin injection were transplanted with human pancreatic islet cells. Mice in which the transplant restored euglycemia were humanized with allogeneic peripheral blood mononuclear cells and treated with ILT3-Fc or control human IgG or left untreated. The blood glucose level was monitored twice a week, and rejection was diagnosed after two consecutive readings >350 mg/dl. Tolerated and rejected grafts were studied histologically and by immunostaining for human T-cells and insulin production. CD4 and CD8 T-cells from the spleen were studied for suppressor activity, expression of cytokines, and CD40L.

RESULTS

Although human T-cell engraftment was similar in all groups, ILT3-Fc-treated mice tolerated the islets for the entire period of observation (91 days), whereas control mice rejected the graft within 7 weeks (P < 0.0001). ILT3-Fc treatment suppressed the expression of cytokines and CD40L and induced the differentiation of human CD8(+) T suppressor cells that inhibited Th alloreactivity against graft HLA antigens. T-cells allostimulated in vitro in the presence of ILT3-Fc inhibited CD40L-induced upregulation of CD40 in human pancreatic islet cells. Histochemical studies showed dramatic differences between human pancreatic islets from tolerant, ILT3-Fc-treated mice and control recipients rejecting the grafts.

CONCLUSIONS

The data indicated that ILT3-Fc is a potent immunoregulatory agent that suppressed islet allograft rejection in humanized NOD/SCID mice.

Prolactin and growth hormone receptors

The two hormones prolactin and growth hormone exhibit considerable structural homology as well as exerting similar biological effects, especially the primate hormones. One effect of prolactin that deserves greater attention is its action on the immune system including the stimulation of growth of experimental lymphomas, both in vivo and in vitro. One cultured lymphoma cell line has proved to be a very useful model system in which to examine prolactin receptor synthesis and turnover as well as post-receptor mechanisms of action. Prolactin and growth hormone receptors from rabbit mammary gland and liver respectively have been partially purified and characterized. Polyclonal antibodies to prolactin and growth hormone receptors have been generated. The antibodies have been shown to cross-react with prolactin or growth hormone receptors from a number of species, indicating structural homology among receptors as well as hormones. The polyclonal antisera inhibit the action of prolactin in vivo as well as in vitro. In addition, several of the same antisera also mimic the action of prolactin. As yet the presence of autoantibodies to prolactin or growth hormone receptors in human serum samples has not been recognized.

The molecular basis of sperm-egg interaction in the sea urchin

In echinoderms the binding of sperm to eggs is a highly species-specific adhesive process. This adhesion is mediated by the interaction between bindin, a protein that coats the sperm acrosomal process, and a high Mr, carbohydrate-rich component of the egg surface. Previous results have shown that sperm binding is destroyed by treatment of the egg surface with proteases. Such treatment results in the release of a carbohydrate-rich fragment that can bind to sperm and inhibit their ability to fertilize eggs. Recent studies have focused on identifying and purifying the sperm receptor from the surface of the eggs of Strongylocentrotus purpuratus and Arbacia punctulata. Purified bindin has been used as a probe to purify an egg surface glycoprotein of very high Mr that can bind to bindin. When this component was added to acrosome-reacted sperm it species-specifically inhibited their ability to fertilize eggs. Antibodies (or Fab fragments of the antibodies) to the glycoprotein receptor coated the egg surface and species-specifically inhibited fertilization. Exhaustive proteolytic digestion of the receptor from S. purpuratus yielded a carbohydrate-rich fragment of high Mr that was highly sulphated. Similar proteolytic treatment of the receptor from A. punctulata yielded an active glycopeptide(s) of much lower Mr that was uncharged. The carbohydrate-rich fragments from both S. purpuratus and A. punctulata bind to acrosome-reacted sperm and inhibit fertilization in nanomolar concentrations. Unlike the respective intact receptors, the fragments do not act species-specifically. From these findings it is concluded that the intact receptor in these two species contains two domains. The carbohydrate-rich domain appears to serve as the adhesive element, whereas the protein component in some way controls accessibility to this adhesive element.

Ligand-independent assembly of purified soluble magic roundabout (Robo4), a tumor-specific endothelial marker

Magic roundabout (Robo4) is the fourth recently identified member of the roundabout receptor family. Robo4 is predominantly expressed in embryonic or tumor vascular endothelium and is considered important for vascular development and as a candidate tumor endothelial marker. Much remains unknown about the Robo4 molecule, however, such as its ligands, structure, and the details of its function. Thus, we aimed to establish an expression and purification method for obtaining soluble recombinant human Robo4 (shRobo4) and mouse Robo4 (smRobo4) for use in Robo4 characterization studies. In this work, we expressed the extracellular domain of hRobo4 and mRobo4 in mammalian 293F cells and purified them by two-step chromatography. Based on gel-filtration chromatography and Blue Native polyacrylamide gel electrophoresis, these purified proteins exist as multimers. The shRobo4 and smRobo4 we obtained will be useful in advanced studies to determine the importance of multimerization, identify the ligands, and elucidate the ligand-receptor interactions and Robo4-mediated signaling. The results of these studies will help to elucidate the role of Robo4 in angiogenesis and perhaps eventually contribute to the development of novel vessel-targeting therapies.

Expression of functional human (pro)renin receptor in silkworm (Bombyx mori) larvae using BmMNPV bacmid

The circulating RA (renin-angiotensin) system is essential for the regulation of blood pressure and electrolyte balance. Recently, plasma prorenin has been reported to significantly increase its level in diabetes and to be possibly non-proteolytically activated by binding to the PRR [(pro)renin receptor] on the cell membrane reported in several tissues during circulation. Although many pathological aspects have been researched, there is a lack of sufficient information on the biochemical structure and biological function of this hPRR (human PRR) because of the difficulty in increasing hPRR expression. In the present study, GFP(uv)-hPRR (hPRR fused with green fluorescence protein when excited with long-wave UV light) was successfully expressed by using BmMNPV (Bombyx mori multiple nucleopolyhedrovirus) bacmid DNA in silkworm (Bombyx mori) larvae. Some of the hPRR was expressed in the haemolymph of silkworm larvae and some of the hPRR was located in the fat body of silkworm larvae. The binding ability of hPRR expressed in the haemolymph and fat body with renin or prorenin was analysed by ELISA and surface plasmon resonance using a biosensor respectively. These binding assays suggest that the expressed hPRR has a functional bioactivity. hPRR preparation in silkworm larvae would, therefore, be useful for biochemical and biomedical researches related to PRR.

Purified mouse egg zona pellucida glycoproteins polymerize into homomeric fibrils under non-denaturing conditions

The mouse egg's zona pellucida (ZP) is composed of three glycoproteins, called ZP1, ZP2, and ZP3, that migrate as relatively broad, single bands on SDS-PAGE. The glycoproteins are organized within the ZP as a network of long interconnected fibrils that exhibit a structural periodicity. Here, ZP2 and ZP3 were purified by HPLC to homogeneity and analyzed by Blue Native- (BN-) PAGE and transmission electron microscopy (TEM), as well as by SDS-PAGE. As opposed to SDS-PAGE, BN-PAGE, and TEM permit analysis of ZP2 and ZP3 under non-denaturing conditions. ZP2 and ZP3 migrate on BN-PAGE, not as single bands, but as several discrete oligomers that give rise to larger structures which remain at the origin of the gel. Consistent with this, ZP2 and ZP3 are visualized by TEM as long interconnected fibrils that consist of contiguous beads. Therefore, under non-denaturing conditions both purified ZP2 and ZP3 polymerize into higher order structures. These findings are of interest since purified ZP3 inhibits binding of mouse sperm to eggs and induces sperm to undergo the acrosome reaction in vitro. Results presented here suggest that these biological effects of ZP3 are due to binding of homomeric fibrils of ZP3 to sperm.

In vivo targeting of DC-SIGN-positive antigen-presenting cells in a nonhuman primate model

In vivo targeting of antigen-presenting cells (APCs) with antigens coupled to antibodies directed against APC-specific endocytic receptors is a simple and a promising approach to induce or modulate immune responses against those antigens. In a recent in vitro study, we have shown that targeting of APCs with an antigen coupled to an antibody directed against the endocytic receptor DC-SIGN effectively induces a specific immune response against that antigen. The aim of the present study was to determine the ability of the murine antihuman DC-SIGN antibody AZN-D1 to target APCs in a cynomolgus macaque model after its administration in vivo. Immunohistochemical analysis demonstrated that macaques injected intravenously with AZN-D1 have AZN-D1-targeted APCs in all lymph nodes (LNs) tested and in the liver. DC-SIGN-positive cells were mainly located in the medullary sinuses of the LNs and in the hepatic sinusoids in the liver. No unlabeled DC-SIGN molecules were found in the LN of AZN-D1-injected macaques. Morphologic criteria and staining of sequential LN sections with a panel of antibodies indicated that the DC-SIGN-targeted cells belong to the myeloid lineage of APCs. In conclusion, this is the first study that shows specific targeting of APCs in vivo by using antibodies directed against DC-SIGN.

[Identification of the beta(2)GPI-binding receptor on hepatocyte membrane]

OBJECTIVE

To identified the beta(2)-glycoprotein I (beta(2)GPI)-bound receptor on the membrane of hepatocellular carcinoma cells, and to analyze its function.

METHODS

Through the beta(2)GPI-affinity chromatography column, the peptide-polysome-mRNA complex specially binding to beta(2)GPI stayed with the column and was separated from the whole polysome of liver cells. Then it was eluted and collected. With the cDNA synthesis kit and cDNA PCR kit, the corresponding cDNA was obtained and sequenced. RT-PCR was used to amplify annexin II, and flow cytometry was used to study the competitive binding of annexin II with beta(2)GPI to SMMC-7721 cells.

RESULTS

1.1 kb cDNA fragment of the specific binding protein of beta(2)GPI on liver cell membrane was obtained. And the sequence of cDNA shared a high homology with human annexin II (98%). Annexin II was expressed on the membrane of the hepatocellular carcinoma cells of the line SMMC-7721, and 1 microl and 4 microl of annexin II caused the binding rate of beta(2)GPI-GFP with SMMC-7721 cells from 15.58% to 13.66% and 7.56% respectively.

CONCLUSION

The receptor of beta(2)GPI on the membrane of hepatocellular carcinoma cells is annexin II, and beta(2)GPI may help HBV invade hepatic cells through combing with annexin II on the liver cell membrane.

Identification of protein-ribulosamine-5-phosphatase as human low-molecular-mass protein tyrosine phosphatase-A

Ribulosamines, which are substrates for the deglycating enzyme fructosamine-3-kinase-related protein, are presumably formed intracellularly through glycation of proteins with ribose 5-phosphate followed by dephosphorylation of resulting RN5Ps (ribulosamine 5-phosphates) by a putative RN5Pase (ribulosamine-5-phosphatase). Ribose 5-phosphate is known to be a potent glycating agent and we show in the present study that it reacts approximately 10 and 80-fold more rapidly with protein than ribose and glucose respectively. We also show that tissue extracts and, most particularly, erythrocyte extracts contain a protein-RN5Pase. We have purified this enzyme from human erythrocytes to near homogeneity and shown it to correspond to LMWPTP-A [low-molecular-mass ('weight') protein tyrosine phosphatase-A]. Human recombinant LMWPTP-A displayed an RN5Pase activity that was higher than its tyrosine phosphatase activity, indicating that this phosphatase may participate in protein deglycation, a new form of protein repair.

Prevention of experimental autoimmune myasthenia gravis by rat Crry-Ig: A model agent for long-term complement inhibition in vivo

Despite its vital role in innate immunity, complement is involved in a number of inflammatory pathologies and has therefore become a therapeutic target. Most agents generated for anti-complement therapy have short half-lives in plasma, or have been of mouse or human origin, thereby limiting their use either to murine models of disease or to short-term therapy. Here we describe the generation of a long-acting rat therapeutic agent based on the rat complement inhibitor, Crry. Characterisation of various soluble forms of Crry demonstrated that the amino-terminal four short-consensus repeat domains were required for full regulatory and C3b-binding activities. Fusion of these domains to rat IgG2a Fc generated an effective complement inhibitor (rCrry-Ig) with a circulating half-life prolonged from 7 min for Crry alone to 53 h for rCrry-Ig. Systemic administration of rCrry-Ig over 5 weeks generated a weak immune response to the recombinant agent, however this was predominantly IgM in nature and did not neutralise Crry function or cause clearance of the agent from plasma. Administration of rCrry-Ig completely abrogated clinical disease in a rat model of myasthenia gravis whereas soluble Crry lacking the immunoglobulin Fc domain caused a partial response. rCrry-Ig not only ablated clinical disease, but also prevented C3 and C9 deposition at the neuromuscular junction and inhibited cellular infiltration at this site. The long half-life and low immunogenicity of this agent will be useful for therapy in chronic models of inflammatory disease in the rat.

The mannose receptor on murine liver sinusoidal endothelial cells is the main denatured collagen clearance receptor

The purpose of this study was to identify the receptor responsible for endocytosis of denatured collagen from blood. The major site of clearance of this material (at least 0.5 g/day in humans) is a receptor on liver sinusoidal endothelial cells (LSECs). We have now identified an 180-kDa endocytic receptor on LSECs, peptide mass fingerprinting of which revealed it to be the mannose receptor. Challenge of mannose-receptor knockout mice and their cultured LSECs revealed significantly reduced blood clearance and a complete absence of LSEC endocytosis of denatured collagen. Organ analysis of wild-type versus knockout mice after injection of denatured collagen revealed significantly reduced liver uptake in the knockout mice. Clearance/endocytosis of ligands for other receptors in these animals was as that for wild-type mice, and denatured collagen uptake in wild-type mice was not affected by other ligands of the mannose receptor, namely mannose and mannan. Furthermore, unlike that of mannose and mannan, endocytosis of denatured collagen by the mannose receptor is calcium independent. This suggests that the binding site for denatured collagen is distinct from that for mannose/mannan. Mannose receptors on LSECs appear to have less affinity for circulating triple helical type I collagen.

CONCLUSION

The mannose receptor is the main candidate for being the endocytic denatured collagen receptor on LSECs.

Characterization of the Outer Membrane Receptor ShuA from the Heme Uptake System of Shigella dysenteriae

Shigella dysenteriae, like many bacterial pathogens, has evolved outer membrane receptor-mediated pathways for the uptake and utilization of heme as an iron source. As a first step toward understanding the mechanism of heme uptake we have undertaken a site-directed mutagenesis, spectroscopic, and kinetic analysis of the outer membrane receptor ShuA of S. dysenteriae. Purification of the outer membrane receptor gave a single band of molecular mass 73 kDa on SDS-PAGE. Initial spectroscopic analysis of the protein in either detergent micelles or lipid bicelles revealed residual heme bound to the receptor, with a Soret maximum at 413 nm. Titration of the protein with exogenous heme gave a Soret peak at 437 nm in detergent micelles, and 402 nm in lipid bicelles. However, transfer of heme from hemoglobin yields a Soret maximum at 413 nm identical to that of the isolated protein. Further spectroscopic and kinetic analysis revealed that hemoglobin in the oxidized state is the most likely physiological substrate for ShuA. In addition, mutation of the conserved histidines, H86A or H420A, resulted in a loss of the ability of the receptor to efficiently extract heme from hemoglobin. In contrast the double mutant H86A/H420A was unable to extract heme from hemoglobin. These findings taken together confirm that both His-86 and His-420 are essential for substrate recognition, heme coordination, and transfer. Furthermore, the full-length TonB was shown to form a 1:1 complex with either apo-ShuA H86A/H420A or the wild-type ShuA. These observations provide a basis for future studies on the coordination and transport of heme by the TonB-dependent outer membrane receptors.

A Cholesterol-independent Membrane Microdomain Serves as a Functional Counter-receptor for E-selectin at the Colo201 Cell Surface and Initiates Signalling on E-selectin Binding

The present study demonstrates that the functional counter-receptors for E-selectin at the cell surface of Colo201 human colon cancer cells are localized in detergent-insoluble membrane microdomains (DIM). Following isolation of counter-receptors from whole cell lysates using E-selectin-coupled magnetic beads followed by sucrose density gradient separation, both sialyl Lewis a (SLe(a))- and sialyl Lewis x (SLe(x))-carrying glycoproteins which had bound to the E-selectin-beads were distributed in detergent-soluble fractions as well as DIM. In contrast, following isolation of counter-receptors directly from the cell surface, SLe(a)-carrying glycoproteins which had bound to E-selectin-beads at the cell surface were localized only in DIM, together with a Src family kinase, Lyn, while SLe(x)-carrying glycoproteins were not detected in any fraction. The counter-receptors were distributed in a diffuse pattern on the cell surface but clustered following E-selectin binding, leading to the subsequent phosphorylation of extracellular signal-regulated kinase (ERK). Treatment of the cells with methyl-beta-cyclodextrin, a cholesterol-depleting drug, had little effect on either the association of SLe(a)-carrying glycoproteins and Lyn with the domain or ERK phosphorylation. Thus, the functional counter-receptors and Lyn are co-localized in a cholesterol-independent microdomain and create a physiological domain ('glycosynapse') at the cell surface that initiates signalling in cancer cells upon binding to E-selectin.

Phenotypic variation in myocardial macrophage populations suggests a role for macrophage activation in SIV-associated cardiac disease

Cardiac abnormalities are common in HIV-infected individuals, and have been especially well documented as contributors to mortality in HIV-infected children. Underlying pathogenetic mechanisms responsible for myocardial disease in HIV-infection remain imperfectly understood. SIV-infected rhesus monkeys develop a spectrum of cardiac lesions similar to those seen in HIV-infected people, providing an important model for pathogenesis studies. Retrospective analysis of cardiac tissue collected at necropsy from SIV-infected rhesus monkeys was performed to evaluate myocardial macrophage and dendritic cell populations as a function of previously quantitated lymphocytic inflammatory infiltrates and cardiomyocyte degeneration or necrosis. Variations in the size and phenotype of macrophage and dendritic cell populations were examined as possible contributors to the pathogenesis of SIV-associated inflammatory lesions. Macrophages labeling immunohistochemically for CD163 differed substantially from macrophages labeling for HAM56 in overall number, distribution across groups, involvement in inflammatory clusters, correlation with the DC-SIGN(+) subpopulation of macrophages, and correlation with numbers of SIV-infected cells. CD163(+) macrophages occurred in significantly higher numbers in uninflamed hearts from SIV-infected animals than in hearts from SIV-infected animals with myocarditis or uninfected controls (p < 0.01). Numbers of CD163(+) cells correlated positively with numbers of SIV-infected cells (p < 0.05) suggesting that the CD163(+) population was associated with decreased inflammatory infiltration and reduced control of virus within the heart. As CD163 has been associated with nonclassical macrophage activation and an antiinflammatory phenotype, these results suggest that a balance between classical and nonclassical activation may affect levels of inflammatory infiltration and of myocardial virus burden.

One-step affinity purification of recombinant urokinase-type plasminogen activator receptor using a synthetic peptide developed by combinatorial chemistry

Several lines of evidence have pointed to a role of urokinase-type plasminogen activator receptor (uPAR) as a modulator of certain biochemical processes that are active during tumor invasion and metastasis. Consequently, the structure and function of this receptor have been studied extensively, using recombinantly produced uPAR that has been purified by either affinity chromatography using its cognate ligand, the urokinase-type plasminogen activator (uPA), or a monoclonal anti-uPAR antibody (R2), or by hydroxyapatite. Here, we present a new method for the efficient one-step affinity purification of recombinant uPAR exploiting a high-affinity synthetic peptide antagonist (AE152). The corresponding parent peptide was originally identified in a random phage-display library and subsequently subjected to affinity maturation by combinatorial chemistry. This study compares the affinity purification of a soluble, recombinant uPAR using the monoclonal antibody R2 or the peptide AE152 immobilized on Sepharose. The two affinity ligands perform equally well in purifying uPAR from Drosophila melanogaster Schneider 2 cell culture medium and yield products of comparable purity, activity, and stability as judged by SDS-PAGE, size exclusion chromatography and surface plasmon resonance analysis. The general availability of peptide synthesis renders the present AE152-based affinity purification of uPAR more accessible than the traditional protein-based affinity purification strategies. In this way, large amounts of recombinant uPAR can conveniently be purified for further structural and functional studies.

Characterization of IQGAP1-containing complexes in NK-like cells: evidence for Rac 2 and RACK1 association during homotypic adhesion

IQGAP1 is a scaffolding protein that binds to a diverse array of signaling and structural molecules that are often associated with cell polarization and adhesion. Through interaction with its target proteins, IQGAP1 participates in multiple cellular functions, including Ca2+-calmodulin signaling, definition of cytoskeletal architecture, regulation of Cdc42 and Rac1 dependent cytoskeletal changes, and control of E-cadherin mediated intercellular adhesion. These analysis have been largely restricted to cells of epithelial and fibroblast origin. The present studies were initiated to examine the role of IQGAP1 in cellular interactions involving the lymphoid cells. A mass spectrometric based analysis of IQGAP1 containing complexes isolated from the human NK-like cell line, YTS, identified several known and new potential IQGAP1 interaction partners including receptor of activated C kinase 1 (RACK1) and the small GTPase, Rac2. Immunofluorescence analysis of YTS cells indicated that a minor component of IQGAP1 was localized at the cell membrane with the remainder diffusely distributed through out the cytoplasm. However, at sites of cellular contact, there was a marked accumulation of IQGAP1. Staining for RACK1 and Rac2 revealed that both of these proteins accumulated these contact sites. Antibody-based studies suggested that a subset of RACK1 was associated in an IQGAP1-containing complex, which prevented recognition of RACK1 by monoclonal antibody. These results suggest that RACK1, Rac2, and IQGAP1 are components of complexes involved in NK cell homotypic adhesion.

Knockdown of aminopeptidase-N from Helicoverpa armigera larvae and in transfected Sf21 cells by RNA interference reveals its functional interaction with Bacillus thuringiensis insecticidal protein Cry1Ac

Aminopeptidase-N (APN) and cadherin proteins located at the midgut epithelium of Helicoverpa armigera have been implicated as receptors for the Cry1A subfamily of insecticidal proteins of Bacillus thuringiensis. Ligand blot analysis with heterologously expressed and purified H. armigera Bt receptor with three closely related Cry1A proteins tentatively identified HaAPN1 as an interacting ligand. However, to date there is no direct evidence of APN being a functional receptor to Cry1Ac in H. armigera. Sf21 insect cells expressing HaAPN1 displayed aberrant cell morphology upon overlaying with Cry1Ac protein. Down-regulating expression of HaAPN1 by RNA interference using double-stranded RNA correlated with a corresponding reduction in the sensitivity of HaAPN1-expressing cells to Cry1Ac protein. This clearly establishes that insect cells expressing the receptor recruit sensitivity to the insecticidal protein Cry1Ac, and their susceptibility is directly dependent on the amount of HaAPN1 protein expressed. Most importantly, silencing of HaAPN1 in H. armigera in vivo by RNA interference resulted in reduced transcript levels and a corresponding decrease in the susceptibility of larvae to Cry1Ac. BIAcore analysis of HaAPN1/Cry1Ac interaction further established HaAPN1 as a ligand for Cry1Ac. This is the first functional demonstration of insect aminopeptidase-N of H. armigera being a receptor of Cry1Ac protein of B. thuringiensis.

Glycoproteins of the vitelline envelope of Amphibian oocyte: Biological and molecular characterization of ZPC component (gp41) inBufo arenarum

The vitelline envelope (VE) participates in sperm-egg interactions during the first steps of fertilization. In Bufo arenarum, this envelope is composed of at least four glycoproteins, with molecular masses of 120, 75, 41, and 38 kDa and molar ratio of 1:1.3:7.4:4.8, respectively. These components were isolated and covalently coupled to silanized glass slides in order to study their sperm-binding capacity. When considering the molar ratio of the glycoproteins in the egg-envelope and assuming that each protein is monovalent for sperm, the assay showed that gp41 and gp38 possess 55 and 25% of total sperm-binding activity. We obtained a full-length cDNA of gp41 (ZPC), comprising a sequence for 486 amino acids, with 43.3% homology with Xenopus laevis ZPC. As in the case of mammalian ZP3 and Xenopus ZPC, Bufo ZPC presented a furin-like (convertase) and a C-terminal transmembrane domain (TMD) reflecting common biosynthetic and secretory pathways. As it was reported for some fishes, we obtained evidence that suggests the presence of more than one zpc gene in Bufo genome, based on different partial cDNA sequences of zpc, Southern blots and two-dimensional SDS-PAGE of deglycosylated egg-envelope components. As far as we are aware, this is the first observation of the presence of different zpc genes in an Amphibian species.

Orphan seven transmembrane receptor screening

Drug discovery has successfully exploited the superfamily of seven transmembrane receptors (7TMR), with over 35% of clinically marketed drugs targeting them. However, it is clear that there remains an undefined potential within this protein family for successful drugs of the future. The human genome sequencing project identified approximately 720 genes that belong to the 7TMR superfamily. Around half of these genes encode sensory receptors, while the other half are potential drug targets. Natural ligands have been identified for approximately 215 of these, leaving 155 receptors classified as orphan 7TMRs having no known ligand. Deorphanisation of these receptors by identification of natural ligands has been the traditional method enabling target validation by use of these ligands as tools to define biological relevance and disease association. Such ligands have been paired with their cognate receptor experimentally by screening of small molecule and peptide ligands, reverse pharmacology and the use of bioinformatics to predict candidate ligands. In this manuscript, we review the methodologies developed for the identification of ligands at orphan 7TMRs and exemplify these with case studies.