Specific detection of his-tagged proteins with recombinant anti-His tag scFv-phosphatase or scFv-phage fusions

Principles and Design of Molecular Tools for Sensing and Perturbing Cell Surface Receptor Activity

Cell-surface receptors are vital for controlling numerous cellular processes with their dysregulation being linked to disease states. Therefore, it is necessary to develop tools to study receptors and the signaling pathways they control. This Review broadly describes molecular approaches that enable 1) the visualization of receptors to determine their localization and distribution; 2) sensing receptor activation with permanent readouts as well as readouts in real time; and 3) perturbing receptor activity and mimicking receptor-controlled processes to learn more about these processes. Together, these tools have provided valuable insight into fundamental receptor biology and helped to characterize therapeutics that target receptors.

A New Rapid Indirect ELISA Test for Serological Diagnosis of Feline Immunodeficiency

The Feline Immunodeficiency Virus (FIV) is a lentivirus belonging to Retroviridae family that affects feline immune cells, causing a progressive immunosuppression by depleting CD4+ T-lymphocytes, similarly to the acquired immune deficiency syndrome (AIDS) in humans caused by human immunodeficiency virus (HIV). Diagnosis is usually performed by clinicians using rapid Enzyme-Linked Immunosorbent Assay (ELISA) or lateral flow tests that detect FIV antibodies. The aim of this work was the development of FIVCHECK Ab ELISA, a new rapid indirect assay for the detection of FIV antibodies in feline serum/plasma samples; FIVCHECK Ab ELISA was developed after a meticulous set-up and cut-off analysis through several methods, including the Youden's index and ROC curve, to achieve the best test performance. The new kit was validated by testing 115 feline sera (38 positives and 77 negatives for FIV antibodies) against the ELISA rapid test SNAP FIV/FeLV Combo (IDEXX). Moreover, 103 sera (28 positives and 75 negatives) were also analyzed with two other rapid indirect ELISAss, INgezim FIV (Gold Standard Diagnostics) and VetLine FIV (NovaTec); FIVCHECK Ab ELISA agreed at 100% with SNAP (100% sensitivity, 95% confidence interval (CI): 88.5-100%; 100% specificity, 95% CI: 94.0-100%), 100% with INgezim FIV and 92.2% with VetLine FIV. Intra- and inter-assay accuracy and precision gave coefficients of variation lower than 10%. The new ELISA is a simple and quick test that provides reliable results for veterinary clinics and practices.

Functional expression and characterization of CAPA receptor in the digestive tract and life stages of Drosophila suzukii, and differential activities with insect PRXamide peptides

Spotted-wing drosophila, Drosophila suzukii (Matsumura), is an invasive vinegar fly that is a major threat to the small fruits industries globally. Insect capa genes encode multiple neuropeptides, including CAPA-periviscerokinin (CAPA-PVK) peptides, that are specifically known to cause diuresis or anti-diuresis in various organisms. Here we identified and characterized a corresponding G protein-coupled receptor (GPCR) of the D. suzukii CAPA-PVK peptides: CAPA receptor (CAPA-R). To better characterize the behavior of D. suzukii CAPA-R, we used insect cell-based functional expression assays to evaluate responses of CAPA-R against D. suzukii CAPA-PVKs, CAPA-PVKs from five species in Insecta, one species from Mollusca, modified CAPA-PVK peptides, and some PRXamide family peptides: pyrokinin (PK), diapause hormone (DH), and ecdysis-triggering hormone (ETH). Functional studies revealed that the D. suzukii CAPA-R is strongly activated by both of its own natural D. suzukii CAPA-PVKs, and interestingly, it was strongly activated by other CAPA-PVK peptides from Frankliniella occidentallis (Thysanoptera), Solenopsis invicta (Hymenoptera), Helicoverpa zea (Lepidoptera) and Plutella xylostella (Lepidoptera). However, D. suzukii CAPA-R was not activated by Mollusca CAPA-PVK or the other PRXamide peptides. Gene expression analyses showed that the CAPA-R was highly expressed in the Malpighian tubules and moderately in hindgut compared to other digestive organs or the rest of body, supporting diuretic/antidiuretic functionality. When compared across life stages of D. suzukii, expression of CAPA-R was approximately 1.5x greater in the third instar than the other stages and minimally detected in the eggs, 4-day old pupae and 3-day old adults. Our results functionally characterized the D. suzukii CAPA-R and a few short peptides were identified as potential biological targets to exploit the CAPA-R for D. suzukii management.

Evaluation of the Inhibitory Potential of Synthetic Peptides Homologous to CDR3 Regions of a Monoclonal Antibody against Bothropic Venom Serine Proteases

Snakebite accidents, neglected tropical diseases per the WHO, pose a significant public health threat due to their severity and frequency. Envenomation by Bothrops genus snakes leads to severe manifestations due to proteolytic enzymes. While the antibothropic serum produced by the Butantan Institute saves lives, its efficacy is limited as it fails to neutralize certain serine proteases. Hence, developing new-generation antivenoms, like monoclonal antibodies, is crucial. This study aimed to explore the inhibitory potential of synthetic peptides homologous to the CDR3 regions of a monoclonal antibody targeting a snake venom thrombin-like enzyme (SVTLE) from B. atrox venom. Five synthetic peptides were studied, all stable against hydrolysis by venoms and serine proteases. Impressively, four peptides demonstrated uncompetitive SVTLE inhibition, with Ki values ranging from 10-6 to 10-7 M. These findings underscore the potential of short peptides homologous to CDR3 regions in blocking snake venom toxins, suggesting their promise as the basis for new-generation antivenoms. Thus, this study offers potential advancements in combatting snakebites, addressing a critical public health challenge in tropical and subtropical regions.

A quantitative comparison of antibodies against epitope tags for immunofluorescence detection

Epitope tags recognized by specific antibodies have been widely used over the last few decades, notably to localize tagged proteins within cells by immunofluorescence. The diversity of tags and antibodies usually prevents a side-by-side comparison of the efficiency with which each antibody recognizes its cognate tag. We expressed chimeric proteins, each composed of an invariant domain (IL2Ra) associated with a specific epitope tag. Double immunofluorescence allowed us to quantify in parallel the reference signal generated by the anti-IL2Ra antibody and the signal generated by the anti-epitope tag antibody. Since all antibodies used in this study were recombinant antibodies fused to the same mouse Fc domain, the generated signals were directly comparable. Three groups of tags/antibodies were revealed: 'good' antibodies generated high signals even when used at a low concentration (50 ng·mL-1 ), 'fair' antibodies generated a high signal only at high concentrations (5000 ng·mL-1 ), and 'mediocre' antibodies generated positive but weak signals. Except for an anti-myc antibody, similar results were obtained when cells were fixed in paraformaldehyde or methanol. These results provide a side-by-side quantitative evaluation of different tag/antibody pairs. This information will be useful to optimize the choice of epitope tags and to choose optimal antibodies.

Development of alkaline phosphatase-scFv and its use for one-step enzyme-linked immunosorbent assay for His-tagged protein detection

A histidine (His)-tag is composed of six His residues and typically exerts little influence on the structure and solubility of expressed recombinant fusion proteins. Purification methods for recombinant proteins containing His-tags are relatively well-established, thus His-tags are widely used in protein recombination technology. We established a one-step enzyme-linked immunosorbent assay (ELISA) for His-tagged recombinant proteins. We analyzed variable heavy and light chains of the anti-His-tag monoclonal antibody 4C9 and used BLAST analyses to determine variable zones in light (VL) and heavy chains (VH). VH, VL, and alkaline phosphatase (ALP) regions were connected via a linker sequence and ligated into the pGEX-4T-1 expression vector. Different recombinant proteins with His tags were used to evaluate and detect ALP-scFv activity. Antigen and anti-His-scFv-ALP concentrations for direct ELISA were optimized using the checkerboard method. ZIKV-NS1, CHIKV-E2, SCRV-N, and other His-tag fusion proteins demonstrated specific reactions with anti-His-scFv-ALP, which were accurate and reproducible when the antigen concentration was 50 µg mL−1 and the antibody concentration was 6.25 µg mL−1. For competitive ELISA, we observed a good linear relationship when coating concentrations of recombinant human anti-Müllerian hormone (hAMH) were between 0.78 and 12.5 µg mL−1. Our direct ELISA method is simple, rapid, and accurate. The scFv antibody can be purified using a prokaryotic expression system, which provides uniform product quality and reduces variations between batches.

Metal-Free Polymer-Based Affinity Medium for Selective Purification of His6-Tagged Proteins

We report a metal free synthetic hydrogel copolymer with affinity and selectivity for His6-tagged peptides and proteins. Small libraries of copolymers incorporating charged and hydrophobic functional groups were screened by an iterative process for His6 peptide affinity. The monomer selection was guided by interactions found in the crystal structure of an anti-His tag antibody-His6 peptide antigen complex. Synthetic copolymers incorporating a phenylalanine-derived monomer were found to exhibit strong affinity for both His6-containing peptides and proteins. The proximity of both aromatic and negatively charged functional groups were important factors for the His6 affinity of hydrogel copolymers. His6 affinity was not compromised by the presence of enzyme cleavage sequences. The His6-copolymer interactions are pH sensitive: the copolymer selectively captured His6 peptides at pH 7.8 while the interactions were substantially weakened at pH 8.6. This provided mild conditions for releasing His6-tagged proteins from the copolymer. Finally, a synthetic copolymer coated chromatographic medium was prepared and applied to the purification of a His6-tagged protein from an E. coli expression system. The results establish that a synthetic copolymer-based affinity medium can function as an effective alternative to immobilized metal ion columns for the purification of His6-tagged proteins.

Construction, characterization and crystal structure of a fluorescent single-chain Fv chimera

In vitro display technologies based on phage and yeast have a successful history of selecting single-chain variable fragment (scFv) antibodies against various targets. However, single-chain antibodies are often unstable and poorly expressed in Escherichia coli. Here, we explore the feasibility of converting scFv antibodies to an intrinsically fluorescent format by inserting the monomeric, stable fluorescent protein named thermal green, between the light- and heavy-chain variable regions. Our results show that the scTGP format maintains the affinity and specificity of the antibodies, improves expression levels, allows one-step fluorescent assay for detection of binding and is a suitable reagent for epitope binning. We also report the crystal structure of an scTGP construct that recognizes phosphorylated tyrosine on FcεR1 receptor of the allergy pathway.

A Library-Based Screening Strategy for the Identification of DARPins as Ligands for Receptor-Targeted AAV and Lentiviral Vectors

Delivering genes selectively to the therapeutically relevant cell type is among the prime goals of vector development. Here, we present a high-throughput selection and screening process that identifies designed ankyrin repeat proteins (DARPins) optimally suited for receptor-targeted gene delivery using adeno-associated viral (AAV) and lentiviral (LV) vectors. In particular, the process includes expression, purification, and in situ biotinylation of the extracellular domains of target receptors as Fc fusion proteins in mammalian cells and the selection of high-affinity binders by ribosome display from DARPin libraries each covering more than 1012 variants. This way, DARPins specific for the glutamate receptor subunit GluA4, the endothelial surface marker CD105, and the natural killer cell marker NKp46 were generated. The identification of DARPins best suited for gene delivery was achieved by screening small-scale vector productions. Both LV and AAV particles displaying the selected DARPins transduced only cells expressing the corresponding target receptor. The data confirm that a straightforward process for the generation of receptor-targeted viral vectors has been established. Moreover, biochemical analysis of a panel of DARPins revealed that their functional cell-surface expression as fusion proteins is more relevant for efficient gene delivery by LV particles than functional binding affinity.

Aberrantly Large Single-Channel Conductance of Polyhistidine Arm-Containing Protein Nanopores

There have been only a few studies reporting on the impact of polyhistidine affinity tags on the structure, function, and dynamics of proteins. Because of the relatively short size of the tags, they are often thought to have little or no effect on the conformation or activity of a protein. Here, using membrane protein design and single-molecule electrophysiology, we determined that the presence of a hexahistidine arm at the N-terminus of a truncated FhuA-based protein nanopore, leaving the C-terminus untagged, produces an unusual increase in the unitary conductance to ∼8 nS in 1 M KCl. To the best of our knowledge, this is the largest single-channel conductance ever recorded with a monomeric β-barrel outer membrane protein. The hexahistidine arm was captured by an anti-polyhistidine tag monoclonal antibody added to the side of the channel-forming protein addition, but not to the opposite side, documenting that this truncated FhuA-based protein nanopore inserts into a planar lipid bilayer with a preferred orientation. This finding is in agreement with the protein insertion in vivo, in which the large loops face the extracellular side of the membrane. The aberrantly large single-channel conductance, likely induced by a greater cross-sectional area of the pore lumen, along with the vectorial insertion into a lipid membrane, will have profound implications for further developments of engineered protein nanopores.

Dual-Functional-Tag-Facilitated Protein Labeling and Immobilization

An important strategy in the construction of biomimetic membranes and devices is to use natural proteins as the functional components for incorporation in a polymeric or nanocomposite matrix. Toward this goal, an important step is to immobilize proteins with high efficiency and precision without disrupting the protein function. Here, we developed a dual-functional tag containing histidine and the non-natural amino acid azidohomoalanine (AHA). AHA is metabolically incorporated into the protein, taking advantage of the Met-tRNA and Met-tRNA synthetase. Histidine in the tag can facilitate metal-affinity purification, whereas AHA can react with an alkyne-functionalized probe or surface via well-established click chemistry. We tested the performance of the tag using two model proteins, green fluorescence protein and an enzyme pyrophosphatase. We found that the addition of the tag and the incorporation of AHA did not significantly impair the properties of these proteins, and the histidine-AHA tag can facilitate protein purification, immobilization, and labeling.

Generation of a Novel Bacteriophage Library Displaying scFv Antibody Fragments from the Natural Buffalo Host to Identify Antigens from Adult Schistosoma japonicum for Diagnostic Development

The development of effective diagnostic tools will be essential in the continuing fight to reduce schistosome infection; however, the diagnostic tests available to date are generally laborious and difficult to implement in current parasite control strategies. We generated a series of single-chain antibody Fv domain (scFv) phage display libraries from the portal lymph node of field exposed water buffaloes, Bubalus bubalis, 11–12 days post challenge with Schistosoma japonicum cercariae. The selected scFv-phages showed clear enrichment towards adult schistosomes and excretory-secretory (ES) proteins by immunofluorescence, ELISA and western blot analysis. The enriched libraries were used to probe a schistosome specific protein microarray resulting in the recognition of a number of proteins, five of which were specific to schistosomes, with RNA expression predominantly in the adult life-stage based on interrogation of schistosome expressed sequence tags (EST). As the libraries were enriched by panning against ES products, these antigens may be excreted or secreted into the host vasculature and hence may make good targets for a diagnostic assay. Further selection of the scFv library against infected mouse sera identified five soluble scFv clones that could selectively recognise soluble whole adult preparations (SWAP) relative to an irrelevant protein control (ovalbumin). Furthermore, two of the identified scFv clones also selectively recognised SWAP proteins when spiked into naïve mouse sera. These host B-cell derived scFvs that specifically bind to schistosome protein preparations will be valuable reagents for further development of a cost effective point-of-care diagnostic test.

Mass drug administration using the highly effective drug praziquantel (PZQ) is currently the method of choice to combat schistosomiasis. However, this treatment regime has limitations; in particular, it does not prevent re-infection and sporadic parasite resistance against PZQ is a continuing threat. The path to the successful control of schistosomiasis is highly challenging and must consider, not only the complex nature of the host-parasite interaction, but also the capacity to assess disease burden and parasite re-emergence in communities where successful control has been achieved. Furthermore, control programs must be economically sustainable in endemic countries and despite significant recent advancements the elimination of schistosomiasis may still be some time away. Accordingly, there is a definitive need to formulate innovative approaches for the development of improved diagnostic tools to accurately assess the disease burden associated with active schistosome infections. Here we describe the usefulness of a phage display library to mature antibody fragments derived from lymph node RNA of the natural buffalo host of the Asian schistosome, Schistosoma japonicum, following an experimental infection. These mature antibody fragments were able to bind native parasite proteins and could thus be used to develop a low cost and accurate point-of-care diagnostic test.

Receptor-targeted lentiviral vectors are exceptionally sensitive toward the biophysical properties of the displayed single-chain Fv

An increasing number of applications require the expression of single-chain variable fragments (scFv) fusion proteins in mammalian cells at the cell surface membrane. Here we assessed the CD30-specific scFv HRS3, which is used in immunotherapy, for its ability to retarget lentiviral vectors (LVs) to CD30 and to mediate selective gene transfer into CD30-positive cells. Fused to the C-terminus of the type-II transmembrane protein hemagglutinin (H) of measles virus and expressed in LV packaging cells, gene transfer mediated by the released LV particles was inefficient. A series of point mutations in the scFv framework regions addressing its biophysical properties, which substantially improved production and increased the melting temperature without impairing its kinetic binding behavior to CD30, also improved the performance of LV particles. Gene transfer into CD30-positive cells increased ∼100-fold due to improved transport of the H-scFv protein to the plasma membrane. Concomitantly, LV particle aggregation and syncytia formation in packaging cells were substantially reduced. The data suggest that syncytia formation can be triggered by trans-cellular dimerization of H-scFv proteins displayed on adjacent cells. Taken together, we show that the biophysical properties of the targeting ligand have a decisive role for the gene transfer efficiency of receptor-targeted LVs.

Effects of actin-like proteins encoded by two Bacillus pumilus phages on unstable lysogeny, revealed by genomic analysis

We characterized two newly isolated myoviruses, Bp8p-C and Bp8p-T, infecting the ginger rhizome rot disease pathogen Bacillus pumilus GR8. The plaque of Bp8p-T exhibited a clear center with a turbid rim, suggesting that Bp8p-T could transform into latent phage. Lysogeny assays showed that both the two phages could form latent states, while Bp8p-T could form latent phage at a higher frequency and stability than Bp8p-C. The genomes of Bp8p-C and Bp8p-T were 151,417 and 151,419 bp, respectively; both encoded 212 putative proteins, and only differed by three nucleotides. Moreover, owing to this difference, Bp8p-C encoded a truncated, putative actin-like plasmid segregation protein Gp27-C. Functional analysis of protein Gp27 showed that Gp27-T encoded by Bp8p-T exhibited higher ATPase activity and assembly ability than Gp27-C. The results indicate that the difference in Gp27 affected the phage lysogenic ability. Structural proteome analysis of Bp8p-C virion resulted in the identification of 14 structural proteins, among which a pectin lyase-like protein, a putative poly-gamma-glutamate hydrolase, and three proteins with unknown function, were firstly identified as components of the phage virion. Both phages exhibited specific lytic ability to the host strain GR8. Bp8p-C showed better control effect on the pathogen in ginger rhizome slices than Bp8p-T, suggesting that Bp8p-C has a potential application in bio-control of ginger rhizome rot disease.

His-tag protein monitoring by a fast mix-and-measure immunoassay

Here, we present a fast mix-and-measure immunoassay for the specific semiquantitative detection of His-tagged proteins, for example in E. coli cell lysate. The assay is based on Förster resonance energy transfer (FRET) between a lanthanide dye-labeled low-affinity His-peptide and an acceptor-labeled anti-His-tag antibody. The targeted His-tag protein in the sample displaces the donor-labeled peptide and leads to a concentration-dependent time-resolved fluorescence signal. The assay has a total assay time of less than two minutes including sample preparation. The assay recognizes both, N- and C-terminally tagged proteins. The detection limit is comparable to those obtained in SDS-PAGE or Western Blot, which are used as standard methods for the characterization of His-tag protein expression. Additionally, we demonstrate a full compatibility of the developed assay to cell lysate, and a correlation to detectable bands in a western blot application. In conclusion, this fast, sensitive, specific and affordable mix-and-measure assay provides a timesaving and user-friendly way to quantify recombinant protein expression. It substantially reduces the workload for recombinant protein detection, especially when His-tag-protein-containing fractions in manual chromatographic purifications have to be identified.

Structural basis of the proinflammatory signaling complex mediated by TSLP

Thymic stromal lymphopoietin (TSLP), a cytokine produced by epithelial cells at barrier surfaces, is pivotal for the development of widespread chronic inflammatory disorders such as asthma and atopic dermatitis. The structure of the mouse TSLP-mediated signaling complex reveals how TSLP establishes extensive interfaces with its cognate receptor (TSLPR) and the shared interleukin 7 receptor α-chain (IL-7Rα) to evoke membrane-proximal receptor-receptor contacts poised for intracellular signaling. Binding of TSLP to TSLPR is a mechanistic prerequisite for recruitment of IL-7Rα to the high-affinity ternary complex, which we propose is coupled to a structural switch in TSLP at the crossroads of the cytokine-receptor interfaces. Functional interrogation of TSLP-receptor interfaces points to putative interaction hotspots that could be exploited for antagonist design. Finally, we derive the structural rationale for the functional duality of IL-7Rα and establish a consensus for the geometry of ternary complexes mediated by interleukin 2 (IL-2)-family cytokines.

scFv antibody: principles and clinical application

To date, generation of single-chain fragment variable (scFv) has become an established technique used to produce a completely functional antigen-binding fragment in bacterial systems. The advances in antibody engineering have now facilitated a more efficient and generally applicable method to produce Fv fragments. Basically, scFv antibodies produced from phage display can be genetically fused to the marker proteins, such as fluorescent proteins or alkaline phosphatase. These bifunctional proteins having both antigen-binding capacity and marker activity can be obtained from transformed bacteria and used for one-step immunodetection of biological agents. Alternatively, antibody fragments could also be applied in the construction of immunotoxins, therapeutic gene delivery, and anticancer intrabodies for therapeutic purposes. This paper provides an overview of the current studies on the principle, generation, and application of scFv. The potential of scFv in breast cancer research is also discussed in this paper.

Fluorescent labeling of antibody fragments using split GFP

Antibody fragments are easily isolated from in vitro selection systems, such as phage and yeast display. Lacking the Fc portion of the antibody, they are usually labeled using small peptide tags recognized by antibodies. In this paper we present an efficient method to fluorescently label single chain Fvs (scFvs) using the split green fluorescent protein (GFP) system. A 13 amino acid tag, derived from the last beta strand of GFP (termed GFP11), is fused to the C terminus of the scFv. This tag has been engineered to be non-perturbing, and we were able to show that it exerted no effect on scFv expression or functionality when compared to a scFv without the GFP11 tag. Effective functional fluorescent labeling is demonstrated in a number of different assays, including fluorescence linked immunosorbant assays, flow cytometry and yeast display. Furthermore, we were able to show that this split GFP system can be used to determine the concentration of scFv in crude samples, as well an estimate of antibody affinity, without the need for antibody purification. We anticipate this system will be of widespread interest in antibody engineering and in vitro display systems.

Conversion of scFv peptide-binding specificity for crystal chaperone development

In spite of advances in protein expression and purification over the last decade, many proteins remain recalcitrant to structure determination by X-ray crystallography. One emerging tactic to obtain high-quality protein crystals for structure determination, particularly in the case of membrane proteins, involves co-crystallization with a protein-specific antibody fragment. Here, we report the development of new recombinant single-chain antibody fragments (scFv) capable of binding a specific epitope that can be introduced into internal loops of client proteins. The previously crystallized hexa-histidine-specific 3D5 scFv antibody was modified in the complementary determining region and by random mutagenesis, in conjunction with phage display, to yield scFvs with new biochemical characteristics and binding specificity. Selected variants include those specific for the hexa-histidine peptide with increased expression, solubility (up to 16.6 mg/ml) and sub-micromolar affinity, and those with new specificity for the EE hexa-peptide (EYMPME) and nanomolar affinity. Complexes of one such chaperone with model proteins harboring either an internal or a terminal EE tag were isolated by gel filtration. The 3.1 Å resolution structure of this chaperone reveals a binding surface complementary to the EE peptide and a ∼52 Å channel in the crystal lattice. Notably, in spite of 85% sequence identity, and nearly identical crystallization conditions, the engineered scFv crystallizes in a different space group than the parent 3D5 scFv, and utilizes two new crystal contacts. These engineered scFvs represent a new class of chaperones that may eliminate the need for de novo identification of candidate chaperones from large antibody libraries.

The use of single chain Fv as targeting agents for immunoliposomes: an update on immunoliposomal drugs for cancer treatment

IMPORTANCE OF THE FIELD

Targeted liposomal drugs represent the next evolution of liposomal drug delivery in cancer treatment. In various preclinical cancer models, antibody-targeted PEGylated liposomal drugs have demonstrated superior therapeutic effects over their non-targeted counterparts. Single chain Fv (scFv) has gained popularity in recent years as the targeting agent of choice over traditional targeting agents such as monoclonal antibodies (mAb) and antibody fragments (e.g., Fab').

AREAS COVERED IN THIS REVIEW

This review is focused mainly on advances in scFv-targeted liposomal drug delivery for the treatment of cancers, based on a survey of the recent literature, and on experiments done in a murine model of human B-lymphoma, using anti-CD19 targeted liposomes targeted with whole mAb, Fab' fragments and scFv fragments.

WHAT THE READER WILL GAIN

This review examines the recent advances in PEGylated immunoliposomal drug delivery, focusing on scFv fragments as targeting agents, in comparison with Fab' and mAb.

TAKE HOME MESSAGE

For clinical development, scFv are potentially preferred targeting agents for PEGylated liposomes over mAb and Fab', owing to factors such as decreased immunogenicity, and pharmacokinetics/biodistribution profiles that are similar to non-targeted PEGylated (Stealth) liposomes.

Targeting of adenovirus serotype 5 pseudotyped with short fiber from serotype 41 to c-erbB2-positive cells using bispecific single-chain diabody

The purpose of the current study was to alter the broad native tropism of human adenovirus for virus targeting to c-erbB2-positive cancer cells. First, we engineered a single-chain antibody (scFv) against the c-erbB2 oncoprotein into minor capsid protein IX (pIX) of adenovirus serotype 5 (Ad5) in a manner commensurate with virion integrity and binding to the soluble extracellular c-erbB2 domain. To ablate native viral tropism and facilitate binding of the pIX-incorporated scFv to cellular c-erbB2, we replaced the Ad5 fiber with the Ad41 short (41s) fiber devoid of all known cell-binding determinants. The resultant Ad5F41sIX6.5 vector demonstrated increased cell binding and gene transfer as compared to the Ad5F41s control; however, this augmentation of virus infectivity was not c-erbB2 specific. Incorporation of a six-histidine (His(6)) peptide into the C-terminus of the 41s fiber protein resulted in markedly increased Ad5F41s6H infectivity in 293AR cells, which express a membrane-anchored scFv against the C-terminal oligohistidine tag, as compared to the Ad5F41s vector and the parental 293 cells. These data suggested that a 41s-fiber-incorporated His(6) tag could serve for attachment of an adapter protein designed to guide Ad5F41s6H infection in a c-erbB2-specific manner. We therefore engineered a bispecific scFv diabody (scDb) combining affinities for both c-erbB2 and the His(6) tag and showed its ability to provide up to 25-fold increase of Ad5F41s6H infectivity in c-erbB2-positive cells. Thus, Ad5 fiber replacement by a His(6)-tagged 41s fiber coupled with virus targeting mediated by an scDb adapter represents a promising strategy to confer Ad5 vector tropism for c-erbB2-positive cancer cells.

Expression of anti-tumor recombinant IgG- and IgE-like genes in eukaryotic cells

The tandem of humanized variable VL and VH genes (ScFv fragment 4D5) possessing a high affinity to the HER-2/neu oncogene (the epidermal growth factor receptor expressed in many types of human tumors) was attached through a flexible linker to the second exon of human antibodies of IgG or IgE isotypes constant gene. The humanized construct of IgE isotype was generated for the first time. Genes of the recombinant antibodies were cloned into the pCl-neo vector under the control of universal cytomegalovirus (CMV) promoter. Transfected HEK-293 cells efficiently produced antibodies of the corresponding isotypes IgE and IgG1. The results of Western blotting confirmed homogeneity of the expressed antibodies, which had the predicted molecular weight and specifically interacted with the HER-2/neu. The attachment of leader peptide to the 5'-end of the gene resulted in the preferential accumulation of recombinant antibodies in the cultural medium. These results indicate that de novo constructed humanized immunoglobulin genes express functionally active, single-chain recombinant antibodies in eukaryotic cells.

A strategy for genetic modification of the spike-encoding segment of human reovirus T3D for reovirus targeting

Human Orthoreovirus Type 3 Dearing is not pathogenic to humans and has been evaluated clinically as an oncolytic agent. Its transduction efficiency and the tumor cell selectivity may be enhanced by incorporating ligands for alternative receptors. However, the genetic modification of reoviruses has been difficult, and genetic targeting of reoviruses has not been reported so far. Here we describe a technique for generating genetically targeted reoviruses. The propagation of wild-type reoviruses on cells expressing a modified sigma 1-encoding segment embedded in a conventional RNA polymerase II transcript leads to substitution of the wild-type genome segment by the modified version. This technique was used for generating reoviruses that are genetically targeted to an artificial receptor expressed on U118MG cells. These cells lack the junction adhesion molecule-1 and therefore resist infection by wild-type reoviruses. The targeted reoviruses were engineered to carry the ligand for this receptor at the C terminus of the sigma 1 spike protein. This demonstrates that the C terminus of the sigma 1 protein is a suitable locale for the insertion of oligopeptide ligands and that targeting of reoviruses is feasible. The genetically targeted viruses can be propagated using the modified U118MG cells as helper cells. This technique may be applicable for the improvement of human reoviruses as oncolytic agents.

Opposite immune reactivity of serum IgG and secretory IgA to conformational recombinant proteins mimicking V1/V2 domains of three different HIV type 1 subtypes depending on glycosylation

The V1/V2 domain of the HIV-1 gp120 envelope protein has been shown to contribute to viral cell tropism during infection and also to viral recognition by neutralizing monoclonal antibodies. However, this domain has been poorly investigated. Carbohydrates have been demonstrated to dramatically influence immune reactivity of antisera to viral glycoprotein antigens. In this study, DNA sequences coding for V1/V2 domains from HIV-1 primary isolates of three subtypes (A, B, and C) were subcloned into a secretion vector and used to transfect CHO cells that are able to achieve the glycosylation of proteins. The structure of purified recombinant V1/V2 proteins was tested using two anti-V1/V2 monoclonal antibodies directed against either a linear or a conformational and glycosylation-dependent epitope (8.22.2 and 697-D). Serum or saliva of 14/82 seropositive patients with anti-V1/V2 reactivity demonstrated good recognition of the recombinant proteins. Deglycosylation of the recombinant proteins was found to increase the reactivity of the serum IgG to the clade A and C but not to clade B V1/V2 domain demonstrating that the recognition of glycosylation sites by serum IgG is clade dependent. When considering SIgA from parotid saliva, deglycosylation of all recombinant proteins tested decreased the reactivity, suggesting that glycosylation plays an important role in the recognition of V1/V2 domain target epitopes by this class of antibodies. In conclusion, these results suggest the influence of carbohydrate moieties on the specificity of the antibodies to the V1/V2 domain produced during HIV infection and the potential importance of viral glycans in vaccine responses after mucosal administration.

Modification of pIX or hexon based on fiberless Ad vectors is not effective for targeted Ad vectors

Adenovirus (Ad) vector application in gene therapy is limited by its naïve tropism. We previously developed protein IX (pIX)-modified and hexon-modified Ad vectors in order to alter Ad vector tropism. However, these modified Ad vectors failed to infect cells with the foreign ligands displayed in the pIX or hexon. We hypothesized that steric hindrance by fiber proteins might have prevented the ligand-mediated transduction, as fibers are the outmost capsid proteins of Ad vectors. Therefore, we generated a series of fiberless Ad vectors and investigated their gene expression properties. Unexpectively, however, pIX- or hexon-modified fiberless Ad vector did not achieve any gene expression (the gene expression level by these vectors was similar to the background level). These results might be caused by the fact that the fiberless particles were weaker against physical burdens. To the best of our knowledge, this study is the first reported attempt to develop fiberless Ad vectors containing foreign ligands in the pIX or hexon region. The drawback of the lower stability of fiberless Ad vectors must be overcome to develop targeted Ad vectors based on such vectors. This study could provide basic information for the development of effective targeted Ad vectors.

Specific in vivo expression in type II pneumocytes of the Jaagsiekte sheep retrovirus long terminal repeat in transgenic mice

Jaagsiekte sheep retrovirus (JSRV) is the causative agent of ovine pulmonary adenocarcinoma, a transmissible lung cancer in sheep. Previous experiments in differentiated murine tissue culture cell lines suggested that the disease specificity of JSRV for secretory lung epithelial cells (type II pneumocytes an Clara cells) reflects transcriptional specificity of the viral long terminal repeat (LTR) for these cells. To test this in vivo, transgenic mice carrying the bacterial beta-galactosidase (beta-Gal) gene driven by the JSRV LTR were generated. Two transgenic lines showed beta-Gal expression in the lungs but not other tissues of F1 animals, although transgene silencing in subsequent generations was a major problem. The cells expressing the transgene were identified by two- and three-color immunofluorescence for marker proteins of type II pneumocytes (surfactant protein C [SPC]) and Clara cells (CC10) as well as for a T7 gene 10 epitope present in the beta-Gal reporter. F1 animals from both lines showed transgene expression in type II pneumocytes, but somewhat surprisingly not in Clara cells. Expression was not detected in bronchiolo-alveolar stem cells (BASCs) either. These results indicate that the JSRV LTR is specifically active in type II pneumocytes in the mouse lung, which is consistent with the fact that JSRV-induced OPA tumors in sheep largely have phenotypic markers of type II pneumocytes.

Directed selection of a conformational antibody domain that prevents mature amyloid fibril formation by stabilizing Abeta protofibrils

The formation of amyloid fibrils is a common biochemical characteristic that occurs in Alzheimer's disease and several other amyloidoses. The unifying structural feature of amyloid fibrils is their specific type of beta-sheet conformation that differentiates these fibrils from the products of normal protein folding reactions. Here we describe the generation of an antibody domain, termed B10, that recognizes an amyloid-specific and conformationally defined epitope. This antibody domain was selected by phage-display from a recombinant library of camelid antibody domains. Surface plasmon resonance, immunoblots, and immunohistochemistry show that this antibody domain distinguishes Abeta amyloid fibrils from disaggregated Abeta peptide as well as from specific Abeta oligomers. The antibody domain possesses functional activity in preventing the formation of mature amyloid fibrils by stabilizing Abeta protofibrils. These data suggest possible applications of B10 in the detection of amyloid fibrils or in the modulation of their formation.

Generation and application of new rat monoclonal antibodies against synthetic FLAG and OLLAS tags for improved immunodetection

Previously, we prepared monoclonal antibodies (mAbs) by immunizing rats with the recombinant fusion proteins of mouse Langerin/CD207, which contained a flexible linker sequence from E. coli OmpF and a FLAG epitope. We found many of new rat mAbs were not reactive to mouse Langerin, and here we identify the epitopes of two of these IgG mAbs, L2 and L5, and assess their efficacy in various immunodetection methods. MAb L5 is a rat IgG mAb against the FLAG epitope, which detected both N-terminal and C-terminal FLAG tagged protein 2 to 8 times better than the conventional anti-FLAG mAb M2 by Western blot. For mAb L2, we found its epitope to be a 14 amino acid sequence SGFANELGPRLMGK which consisted of both sequences from the OmpF derived linker and mouse Langerin. This epitope sequence was named OLLAS (E. coliOmpF Linker and mouse Langerin fusion Sequence), and mAb L2 as mAb OLLA-2. When the OLLAS sequence was inserted into recombinant proteins at N-terminal, C-terminal, or internal sites, the OLLAS tag was detected by mAb OLLA-2 with very high sensitivity compared to other conventional epitope tags and anti-tag mAbs. MAb OLLA-2 recognized OLLAS tagged proteins with at least 100-fold more sensitivity than anti-FLAG M2 and anti-V5 mAbs in Western blot analyses. We also find the OLLAS epitope to be superior in immunoprecipitation and other immunodetection methods, such as fluorescent immunohistochemistry and flow cytometry. In the process, we successfully utilized the OLLAS epitope sequence as an internal linker for fusion between the engineered mAb and the antigen, and thus achieved improved immunodetection.

A dual expression platform to optimize the soluble production of heterologous proteins in the periplasm of Escherichia coli

The functional analysis of individual proteins or of multiprotein complexes - since the completion of several genome sequencing projects - is in focus of current scientific work. Many heterologous proteins contain disulfide-bonds, required for their correct folding and activity, and therefore, need to be transported to the periplasm. The production of soluble and functional protein in the periplasm often needs target-specific regulatory genetic elements, leader peptides, and folding regimes. Usually, the optimization of periplasmic expression is a step-wise and time-consuming procedure. To overcome this problem we developed a dual expression system, containing a degP-promoter-based reporter system and a highly versatile plasmid set. This combines the differential protein expression with the selection of a target-specific expression plasmid. For the validation of this expression tool, two different molecular formats of a recombinant antibody directed to the human epidermal growth factor receptor and human 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) were used. By application of this expression system we demonstrated that the amount of functional protein is inversely proportional to the on-line luciferase signal. We showed that this technology offers a simple tool to evaluate and improve the yield of functionally expressed proteins in the periplasm, which depends on the used regulatory elements and folding strategies.

Species and epitope specificity of two 65 kDa glutamate decarboxylase time-resolved fluorometric immunoassays

The 65 kDa isoform of human glutamate decarboxylase (GAD65) is a major autoantigen in type 1 diabetes (T1D). In the present study, we have developed a sensitive sandwich time-resolved fluorescence immunoassay (TRFIA) for the quantification of GAD65 in cell extracts, cell media and serum. The monoclonal antibody GAD-6 is used to selectively capture GAD65 but not the slightly larger isoform GAD67, and the utilization of different detecting antibodies with distinct GAD65 epitope specificity allows modulating the specificity of the assay. To this effect we have biotinylated a recombinant antigen-binding fragment (rFab) with epitope specificity for the N-terminal region of rat and human GAD65 (rFab N-GAD65) and another rFab that selectively binds to the middle part of human GAD65 (rFab b96.11). In the assay the biotinylated rFabs are recognized by Europium labeled streptavidin. The obtained time-resolved fluorescence (TRF) is directly proportional to the concentration of GAD65 over a large measuring range (0.1 to >100 ng/mL). Based on total error estimation including both bias and imprecision, the lower limit of quantitation (LLOQ) of GAD65 in cell extracts is 0.33 ng/mL with the N-GAD65 TRFIA, and 0.10 ng/mL with the b96.11 TRFIA, but the latter is suitable for human GAD65 only, whereas the N-GAD65 TRFIA has equal sensitivity with rat and human GAD65. Specificity was further checked with GAD65/67 fusion proteins, confirming that the presence of intact capture as well as detection epitope on the analyte is a prerequisite for recognition in both assays. We show that the beta cell-specific marker GAD65 can be quantified in pancreatic cell extracts and in serum, allowing studies on discharge during cell death in vitro as well as in vivo.

Using Phage Display to Select Antibodies Recognizing Post-translational Modifications Independently of Sequence Context

Many cellular activities are controlled by post-translational modifications, the study of which is hampered by the lack of specific reagents due in large part to their ubiquitous and non-immunogenic nature. Although antibodies against specifically modified sequences are relatively easy to obtain, it is extremely difficult to derive reagents recognizing post-translational modifications independently of the sequence context surrounding the modification. In this study, we examined the possibility of selecting such antibodies from large phage antibody libraries using sulfotyrosine as a test case. Sulfotyrosine is a post-translational modification important in many extracellular protein-protein interactions, including human immunodeficiency virus infection. After screening almost 8000 selected clones, we were able to isolate a single specific single chain Fv using two different selection strategies, one of which included elution with tyrosine sulfate. This antibody was able to recognize sulfotyrosine independently of its sequence context in test peptides and a number of different natural proteins. Antibody reactivity was lost by antigen treatment with sulfatase or preincubation with soluble tyrosine sulfate, indicating its specificity. The isolation of this antibody signals the potential of phage antibody libraries in the derivation of reagents specific for post-translational modifications, although the extensive screening required indicates that such antibodies are extremely rare.

The effect of the hexahistidine-tag in the oligomerization of HSC70 constructs

The hexahistidine is a fusion tag used for the isolation of proteins via an immobilized metal-ion affinity chromatography (IMAC). In the present study, we have purified and analyzed two constructs of the heat shock protein HSC70 in the presence or the absence of the His-tag (C30WT-His(+)/C30WT and C30DeltaL-His(+)/C30DeltaL). The oligomerization properties of the constructs were analyzed by size exclusion chromatography (SEC) and analytical ultracentrifugation (AU). Results from SEC analysis indicated that the His-tag promotes the dimerization of C30DeltaL-His(+) but has no effect on the elution profile of C30WT-His(+), compared to their respective untagged forms C30DeltaL and C30WT. These observations were also confirmed by AU analysis which indicates that C30DeltaL is stabilized in the dimeric form in the presence of the His-tag. These results emphasize the need to remove the His-tag before structural characterization of some recombinant proteins.

Eukaryotic expression of human arresten gene and its effect on the proliferation of vascular smooth muscle cells

The eukaryotic expression of human arresten gene and its effect on the proliferation of in vitro cultured vascular smooth cells (VSMCs) in vitro were investigated. COS-7 cells were transfected with recombinant eukaryotic expression plasmid pSecTag2-AT or control plasmid pSecTag2 mediated by liposome. Forty-eight h after transfection, reverse transcription-polymerase chain reaction (RT-PCR) was used to detect the expression of arresten mRNA in the cells, while Western blot assay was applied to detect the expression of arresten protein in concentrated supernatant. Primary VSMCs from thoracic aorta of male Sprague-Dawley rats were cultured using the tissue explant method, and identified by immunohistochemical staining with a smooth muscle-specific anti-alpha-actin monoclonal antibody before serial subcultivation. VSMCs were then co-cultured with the concentrated supernatant and their proliferation was detected using Cell Counting Kit-8 (CCK-8) in vitro. The results showed that RT-PCR revealed that the genome of arresten-transfected cells contained a 449 bp specific fragment of arresten gene, suggesting the successful transfection. Successful protein expression in supernatants was confirmed by Western blot. CCK-8 assay showed that the proliferation of VSMCs were inhibited significantly by arresten protein as compared with control cells (F=40.154, P<0.01). It was concluded that arresten protein expressed in eukaryotic cells can inhibit proliferation of VSMCs effectively in vitro, which would provide possibility to the animal experiments.

Redirecting coronavirus to a nonnative receptor through a virus-encoded targeting adapter

Murine hepatitis coronavirus (MHV)-A59 infection depends on the interaction of its spike (S) protein with the cellular receptor mCEACAM1a present on murine cells. Human cells lack this receptor and are therefore not susceptible to MHV. Specific alleviation of the tropism barrier by redirecting MHV to a tumor-specific receptor could lead to a virus with appealing properties for tumor therapy. To demonstrate that MHV can be retargeted to a nonnative receptor on human cells, we produced bispecific adapter proteins composed of the N-terminal D1 domain of mCEACAM1a linked to a short targeting peptide, the six-amino-acid His tag. Preincubation of MHV with the adapter proteins and subsequent inoculation of human cells expressing an artificial His receptor resulted in infection of these otherwise nonsusceptible cells and led to subsequent production of progeny virus. To generate a self-targeted virus able to establish multiround infection of the target cells, we subsequently incorporated the gene encoding the bispecific adapter protein as an additional expression cassette into the MHV genome through targeted RNA recombination. When inoculated onto murine LR7 cells, the resulting recombinant virus indeed expressed the adapter protein. Furthermore, inoculation of human target cells with the virus resulted in a His receptor-specific infection that was multiround. Extensive cell-cell fusion and rapid cell killing of infected target cells was observed. Our results show that MHV can be genetically redirected via adapters composed of the S protein binding part of mCEACAM1a and a targeting peptide recognizing a nonnative receptor expressed on human cells, consequently leading to rapid cell death. The results provide interesting leads for further investigations of the use of coronaviruses as antitumor agents.

Stably Transformed Insect Cell Lines: Tools for Expression of Secreted and Membrane‐anchored Proteins and High‐throughput Screening Platforms for Drug and Insecticide Discovery

Insect cell-based expression systems are prominent amongst current expression platforms for their ability to express virtually all types of heterologous recombinant proteins. Stably transformed insect cell lines represent an attractive alternative to the baculovirus expression system, particularly for the production of secreted and membrane-anchored proteins. For this reason, transformed insect cell systems are receiving increased attention from the research community and the biotechnology industry. In this article, we review recent developments in the field of insect cell-based expression from two main perspectives, the production of secreted and membrane-anchored proteins and the establishment of novel methodological tools for the identification of bioactive compounds that can be used as research reagents and leads for new pharmaceuticals and insecticides.

Novel antibody tags from the rat lysosomal protein RT1.DM for immunodetection of recombinant proteins

Previously, two mouse monoclonal antibodies (12B8 and 6D4) were raised against the alpha- and beta-subunits of the rat non-classical MHC class-II heterodimer RT1.DM. Here, I describe the epitope mapping of mAb 12B8 to amino acids alpha3-14 (EASPQAWWDESQ) and mAb 6D4 to amino acids beta35-44 (WDPEEGQIVP). Epitope mapping was conducted by preparing fusion proteins between the alpha and beta chain of RT1.DM for Western detection with mAb 12B8 and 6D4. By mutating non-conserved amino acids of the human orthologue of RT1.DM, the rat epitopes were introduced, thereby making the alpha and beta polypeptides sensitive for mAb 12B8 and 6D4 detection. The epitopes, designated as 12B8 and 6D4, were tested for protein tagging. They were appended to the N- or C-terminus of four human proteins, the tumour suppressor protein VHL (von Hippel-Lindau), SUMO4, MHC class-II DQbeta and -DPbeta for expression in mammalian cells. Western detection, immunoprecipitation and localisation of the tagged proteins were successfully demonstrated. Thus, the 12B8 and 6D4 epitope tag can be universally used for the immunodetection of recombinant proteins and to study protein-protein interactions.

Design of multivalent complexes using the barnase*barstar module

The ribonuclease barnase (12 kDa) and its inhibitor barstar (10 kDa) form a very tight complex in which all N and C termini are accessible for fusion. Here we exploit this system to create modular targeting molecules based on antibody scFv fragment fusions to barnase, to two barnase molecules in series and to barstar. We describe the construction, production and purification of defined dimeric and trimeric complexes. Immobilized barnase fusions are used to capture barstar fusions from crude extracts to yield homogeneous, heterodimeric fusion proteins. These proteins are stable, soluble and resistant to proteolysis. Using fusions with anti-p185(HER2-ECD) 4D5 scFv, we show that the anticipated gain in avidity from monomer to dimer to trimer is obtained and that favorable tumor targeting properties are achieved. Many permutations of engineered multispecific fusion proteins become accessible with this technology of quasi-covalent heterodimers.

Sigma 54 levels and physiological control of the Pseudomonas putida Pu promoter

The cellular levels of the alternative sigma factor sigma(54) of Pseudomonas putida have been examined in a variety of growth stages and culture conditions with a single-chain Fv antibody tailored for detection of scarce proteins. The levels of sigma(54) were also monitored in P. putida strains with knockout mutations in ptsO or ptsN, known to be required for the C-source control of the sigma(54)-dependent Pu promoter of the TOL plasmid. Our results show that approximately 80 +/- 26 molecules of sigma(54) exist per cell. Unlike that in relatives of Pseudomonas (e.g., Caulobacter), where fluctuations of sigma(54) determine adaptation and differentiation when cells face starvation, sigma(54) in P. putida remains unexpectedly constant at different growth stages, in nitrogen starvation and C-source repression conditions, and in the ptsO and ptsN mutant strains analyzed. The number of sigma(54) molecules per cell in P. putida is barely above the predicted number of sigma(54)-dependent promoters. These figures impose a framework on the mechanism by which Pu (and other sigma(54)-dependent systems) may become amenable to physiological control.

Production, purification and characterisation of genetically derived scFv and bifunctional antibody fragments capable of detecting illicit drug residues

We have generated a single chain antigen binding protein (scFv) recognising morphine. Variable regions of heavy (V(H)) and light (V(L)) chain antibody genes isolated from a murine immune repertoire were connected via a glycine-serine linker and cloned into the expression vector pAK 400. The scFv was produced in Escherichia coli JM83 yielding a functional protein of approximately M(r) 30000. Immunoaffinity chromatography using M3G-BSA-Sepharose column proved most effective for scFv purification. Purity was monitored by SDS-PAGE and Western blotting and the scFv characterised using ELISA and BIAcore. The scFv was capable of specifically binding free morphine in solution and was applicable to real sample analysis in saliva. In order to express a bivalent "minibody" the scFv gene was recloned into a vector containing a gene encoding a helix for dimerisation. The scFv was expressed as a protein of M(r) 75000 and retained its antibody binding capabilities. Cloning the scFv gene into a vector containing the bacterial alkaline phosphatase gene produced a bifunctional molecule, which retained the binding activity of the parental scFv along with the enzymatic activity of alkaline phosphatase.

Fluorescence detection and quantitation of recombinant proteins containing oligohistidine tag sequences directly in sodium dodecyl sulfate-polyacrylamide gels

Two fluorophore-nitrilotriacetic acid conjugates, Pro-Q Sapphire 365 and Pro-Q Sapphire 488 oligohistidine gel stains, have been developed for the fluorescence detection of fusion proteins containing oligohistidine tags directly in sodium dodecyl sulfate polyacrylamide gels, without the requirement for electroblotting, reporter enzymes or secondary detection reagents. Pro-Q Sapphire 365 oligohistidine gel stain exhibits bright-blue fluorescence (emission maximum = 450 nm) when illuminated with UV-A or UV-B light from a standard ultraviolet transilluminator. Pro-Q Sapphire 488 oligohistidine gel stain exhibits bright-green fluorescence (emission maximum = 515 nm) when illuminated with visible light from a laser-based gel scanner equipped with a 470 nm second-harmonic generation (SHG) or 488 nm argon-ion laser source. Typically, 25-65 ng of oligohistidine-tagged fusion protein in whole cell lysates is detectable using either stain. After documenting the fluorescence signal from the Pro-Q Sapphire dyes, gels may be post-stained with the red-fluorescent SYPRO Ruby protein gel stain in order to reveal the total protein pattern.

Generation of an adenoviral vector containing an addition of a heterologous ligand to the serotype 3 fiber knob

As an initial assessment of the feasibility of employing the adenovirus serotype 3 (Ad3) fiber knob as a locale for introducing a tropism-modifying motif, we generated an adenoviral vector containing a six-histidine tag genetically fused to the carboxy-terminus of the Ad3 fiber knob. The heterologous tag proved to be accessible for binding in the context of the virion and, moreover, had rendered the modified vector capable of mediating gene transfer through an artificial, non-Ad3 receptor.

Biophysical properties of human antibody variable domains

There are great demands on the stability, expression yield and resistance to aggregation of antibody fragments. To untangle intrinsic domain effects from domain interactions, we present first a systematic evaluation of the isolated human immunoglobulin variable heavy (V(H)) and light (V(L)) germline family consensus domains and then a systematic series of V(H)-V(L) combinations in the scFv format. The constructs were evaluated in terms of their expression behavior, oligomeric state in solution and denaturant-induced unfolding equilibria under non-reducing conditions. The seven V(H) and seven V(L) domains represent the consensus sequences of the major human germline subclasses, derived from the Human Combinatorial Antibody Library (HuCAL). The isolated V(H) and V(L) domains with the highest thermodynamic stability and yield of soluble protein were V(H)3 and V(kappa)3, respectively. Similar measurements on all domain combinations in scFv fragments allowed the scFv fragments to be classified according to thermodynamic stability and in vivo folding yield. The scFv fragments containing the variable domain combinations H3kappa3, H1bkappa3, H5kappa3 and H3kappa1 show superior properties concerning yield and stability. Domain interactions diminish the intrinsic differences of the domains. ScFv fragments containing V(lambda) domains show high levels of stability, even though V(lambda) domains are surprisingly unstable by themselves. This is due to a strong interaction with the V(H) domain and depends on the amino acid sequence of the CDR-L3. On the basis of these analyses and model structures, we suggest possibilities for further improvement of the biophysical properties of individual frameworks and give recommendations for library design.

Cytopathic effects observed upon expression of a repressed collagenase gene present in Salmonella and related pathogens: mimicry of a cytotoxin from multiple antibiotic-resistant Salmonella enterica serotype Typhimurium phagetype DT104

Recently, we reported that certain strains of Salmonella enterica serovar Typhimurium phagetype DT104 (DT104) secrete a putative cytotoxin. While searching for the gene that encodes this toxin, we noted a previously reported but uncharacterized DNA fragment (clg) in Salmonella that could be potentially relevant to cytotoxin-like activity. Therefore, we cloned and expressed clg in cytotoxin-negative Escherichia coli and Salmonella and subsequently assessed the bioactivity of Clg in vitro and in vivo. Lysates containing Clg from both expression hosts exerted cytopathic effects on murine enterocytes while semi-purified Clg was determined to be cytopathic to HEp-2 cells. Sequence and RT-PCR analyses of the clg gene indicated that a homologue of clg exists in different Gram-negative bacteria although the gene is not expressed in vitro. Although Clg-mediated lesions are similar to those mediated by the DT104 cytotoxin, further investigations are necessary to examine the relationship between these two proteins in DT104. Nonetheless, we report here a defined Salmonella protein that is capable of inflicting damage on tissue culture cells and murine enterocytes.

Construction and characterization of protein libraries composed of secondary structure modules

Only a minute fraction of all possible protein sequences can exist in the genomes of all life forms. To explore whether physicochemical constraints or a lack of need causes the paucity of different protein folds, we set out to construct protein libraries without any restriction of topology. We generated different libraries (all alpha-helix, all beta-strand, and alpha-helix plus beta-strand) with an average length of 100 amino acid residues, composed of designed secondary structure modules (alpha-helix, beta-strand, and beta-turn) in various proportions, based primarily on the patterning of polar and nonpolar residues. We wished to explore that part of sequence space that is rich in secondary structure. The analysis of randomly chosen clones from each of the libraries showed that, despite the low sequence homology to known protein sequences, a substantial proportion of the library members containing alpha-helix modules were indeed helical, possess a defined oligomerization state, and showed cooperative chemical unfolding behavior. On the other hand, proteins composed of mainly beta-strand modules tended to form amyloid-like fibrils and were among the least soluble proteins ever reported. We found that a large fraction of members in non-beta-strand-containing protein libraries that are distant from natural proteins in sequence space possess unexpectedly favorable properties. These results reinforce the efficacy of applying binary patterning to design proteins with native-like properties despite lack of restriction in topology. Because of the intrinsic tendency of beta-strand modules to aggregate, their presence requires precise topologic arrangement to prevent fibril formation.

A peptide derived from cyclin-dependent kinase activator (p35) specifically inhibits Cdk5 activity and phosphorylation of tau protein in transfected cells

Cyclin-dependent kinase-5 (Cdk5) is a serine/threonine kinase activated by its neuron-specific activator, p35, or its truncated form, p25. It has been proposed that the deregulation of Cdk5 activity by association with p25 in human brain tissue disrupts the neuronal cytoskeleton and may be involved in neurodegenerative diseases such as Alzheimer's disease. In this study, we demonstrate that a short peptide (amino acid residues 154-279; Cdk5 inhibitory peptide; CIP), derived from p35, specifically inhibits Cdk5 activity in vitro and in HEK293 cells cotransfected with the peptide and Cdk5/p25, but had no effect on endogenous cdc2 kinase activity. Moreover, we demonstrate that the phosphorylation of tau in HEK293 cells, cotransfected with Cdk5/p25 and CIP, is effectively reduced. These results suggest that CIP specifically inhibits both Cdk5/p25 complex activity and the tau hyperphosphorylation induced by Cdk5/p25. The elucidation of the molecular basis of p25 activation and CIP inhibition of Cdk5 activity may provide insight into mechanisms underlying the pathology of Alzheimer's disease and contribute to therapeutic strategies.

Crystal structure of the anti-His tag antibody 3D5 single-chain fragment complexed to its antigen

The crystal structure of a mutant form of the single-chain fragment (scFv), derived from the monoclonal anti-His tag antibody 3D5, in complex with a hexahistidine peptide has been determined at 2.7 A resolution. The peptide binds to a deep pocket formed at the interface of the variable domains of the light and the heavy chain, mainly through hydrophobic interaction to aromatic residues and hydrogen bonds to acidic residues. The antibody recognizes the C-terminal carboxylate group of the peptide as well as the main chain of the last four residues and the last three imidazole side-chains. The crystals have a solvent content of 77% (v/v) and form 70 A-wide channels that would allow the diffusion of peptides or even small proteins. The anti-His scFv crystals could thus act as a framework for the crystallization of His-tagged target proteins. Designed mutations in framework regions of the scFv lead to high-level expression of soluble protein in the periplasm of Escherichia coli. The recombinant anti-His scFv is a convenient detection tool when fused to alkaline phosphatase. When immobilized on a matrix, the antibody can be used for affinity purification of recombinant proteins carrying a very short tag of just three histidine residues, suitable for crystallization. The experimental structure is now the basis for the design of antibodies with even higher stability and affinity.