Phage Enzyme-linked Immunosorbent Assay Research Articles

Generating the human asialoglycoprotein receptor specific scFv by capture phage ELISA

目的 评价捕获噬菌体酶免疫吸附试验法(ELISA)在筛选抗去唾液酸糖蛋白受体(ASGPR)单链抗体(scFv)中的价值.方法以含ASGPR基因的质粒(CRDH1/pET3b)为模板,通过聚合酶链反应扩增获得ASGPR H1亚单位糖识别区基因(CRDH1),定向克隆至原核表达载体pET-32c,并经IPTG诱导表达,其表达产物用Ni2+螯合柱亲和纯化;然后,采用捕获噬菌体ELISA对人源噬菌体抗体库进行筛选和鉴定,同时对筛选的抗CRDH1单链抗体进行DNA测序、表达、纯化和免疫印记鉴定.然后,与间接噬菌体ELISA比较.结果 CRDH1/pET-32c在原核系统中经诱导表达出分子量约35 000的融合蛋白,且以包涵体形式存在;通过Ni2+亲和柱纯化获得CRDH1融合蛋白后,采用捕获噬菌体ELISA进行四轮筛选,在60个噬菌体克隆中有45株与CRDH1特异性结合,其中仅1株与重组蛋白标签有交叉结合反应.DNA序列分析表明,有9株DNA序列各异,9株可分泌性表达与CRDH1特异性结合的scFv,纯化的scFv也可特异性识别rCRDH1.计算该筛选方法的假阳性率为2%,低于间接噬菌体ELISA筛选的假阳性率(58%).结论捕获噬菌体ELISA筛选CRDH1特异性scFv可有效降低硫氧还蛋白标签(Trx·Tag)引起的假阳性,提高筛选阳性率,并成功筛选出9株具有rCRDH1特异性的scFv。

Protein Kinase C-related Kinase 2 Regulates Hepatitis C Virus RNA Polymerase Function by Phosphorylation

The hepatitis C virus (HCV) NS5B protein is the viral RNA-dependent RNA polymerase required for replication of the HCV RNA genome. We have identified a peptide that most closely resembles a short region of the protein kinase C-related kinase 2 (PRK2) by screening of a random 12-mer peptide library displayed on the surface of the M13 bacteriophage with NS5B proteins immobilized on microwell plates. Competitive phage enzyme-linked immunosorbent assay with a synthetic peptide showed that the phage clone displaying this peptide could bind HCV RNA polymerase with a high affinity. Coimmunoprecipitation and colocalization studies demonstrated in vivo interaction of NS5B with PRK2. In vitro kinase assays demonstrated that PRK2 specifically phosphorylates NS5B by interaction with the N-terminal finger domain of NS5B (amino acids 1-187). Consistent with the in vitro NS5B-phosphorylating activity of PRK2, we detected the phosphorylated form of NS5B by metabolic cell labeling. Furthermore, HCV NS5B immunoprecipitated from HCV subgenomic replicon cells was specifically recognized by an antiphosphoserine antibody. Knock-down of the endogenous PRK2 expression using a PRK2-specific small interfering RNA inhibited HCV RNA replication. In contrast, PRK2 overexpression, which was accompanied by an increase of in the level of its active form, dramatically enhanced HCV RNA replication. Altogether, our results indicate that HCV RNA replication is regulated by NS5B phosphorylation by PRK2.

Efficient isolation of cDNA clones encoding rheumatoid arthritis autoantigens by lambda phage surface display

Bacteriophage lambda surface display was used to isolate cDNA clones encoding autoantigens recognized by synovial fluid (SF) or sera from patients with rheumatoid arthritis (RA). We constructed cDNA libraries from human synovial sarcoma cells and synovial tissue, using the surface display vector λfoo. The cDNA libraries were screened by affinity selection using 40 SF and 44 sera as probes separately immobilized in microtiter wells. Phage clones isolated encode 13 different autoantigens; an unknown protein, two proteins previously unanalyzed as autoimmune antigens, three proteins previously unknown to be recognized by RA sera, and seven known RA antigens. When analyzed their sensitivity and specificity for RA by phage enzyme-linked immunosorbent assay, frequencies of sera that recognize the newly-isolated autoantigens ranged from 20.5 to 6.8% of a panel of RA sera, and 13.6–0% of other autoimmune disease sera. These results indicate that the lambda phage surface display may be powerful for the isolation of cDNA clones encoding autoantigens recognized by SF or sera from patients with not only RA but also other autoimmune diseases.

A Substrate Phage Enzyme-Linked Immunosorbent Assay to Profile Panels of Proteases

It is estimated that proteases comprise nearly 2% of the human genome. Given that the primary structure of all known proteases will soon be available, an important challenge is to define the structure-activity relationships that govern substrate hydrolysis. Ideally this would be accomplished on a genome-wide scale. To this end, we have developed a one-pot phage selection system that yields the substrate recognition profile of multiple proteases from a single round of selection. The system meets five key criteria: (i) multiple proteases can be analyzed simultaneously, (ii) prior knowledge of substrate preference is not required, (iii) information regarding substrate preferences on both side of the scissile bond is obtained, (iv) the system yields selective substrates that distinguish closely related proteases, and (v) semiquantitative information on substrate hydrolysis is obtained, allowing for the assignment of initial rank-order preferences. As an illustration, a phage selection with a mixture of thrombin and factor Xa (serine proteases) along with matrix-metalloproteinase-9 and atrolysin C (metalloproteinases) was performed. Peptide substrates were identified that (i) have high k cat/ K m ratios, (ii) are selective for individual proteases, and (iii) match the sequences of known physiological substrates.

GST fusion proteins cause false positives during selection of viral movement protein specific single chain antibodies

Glutathione S-transferase (GST) fusion proteins are used frequently for investigating protein–protein and protein-DNA interactions. The present study demonstrates that the use of GST fusion proteins caused false positives during selection of phage-displayed single-chain antibody fragments (scFvs) specific for three domains of the movement protein (NS M) of tomato spotted wilt virus (TSWV). To identify and exclude the false positives when using GST as a fusion partner linked to the antigen of interest, indirect phage enzyme-linked immunosorbent assay (ELISA) was compared with capture phage ELISA. Of 210 enriched phage clones, indirect phage ELISA identified 106 clones specific for binding to GST-domain fusions but not to GST. In contrast, using capture phage ELISA, all 106 selected clones were identified as false positives, reacting with the GST fusion proteins and GST. This was confirmed by characterization of soluble scFv antibodies. The data indicate that GST fusion proteins seem unsuitable for screening of phage-displayed antibody fragments and it is essential to use capture phage ELISA, instead of the indirect phage ELISA used commonly to exclude false positives in characterization of selected clones with GST fusion proteins.

Display of functional beta-lactamase inhibitory protein on the surface of M13 bacteriophage.

The display of proteins on the surface of filamentous phage has been shown to be a powerful method to select variants of a protein with altered binding properties from large combinatorial libraries of mutants. The beta-lactamase inhibitory protein (BLIP) is a 165-amino-acid protein that binds and inhibits TEM-1 beta-lactamase-catalyzed hydrolysis of the penicillin and cephalosporin antibiotics. Here we describe the construction of a new phagemid vector and the use of this vector to display BLIP on the surface of filamentous phage. It is shown that BLIP-displaying phage bind to immobilized beta-lactamase and that the binding can be competed off by the addition of soluble beta-lactamase. In addition, a two-step phage enzyme-linked immunosorbent assay procedure was used to demonstrate that the BLIP-displaying phage bind beta-lactamase with a 50% inhibitory concentration of 1 nM, which compares favorably with a previously published Ki of 0.6 nM. A system has therefore been established for protein engineering of BLIP to expand its range of binding to other beta-lactamases and penicillin-binding proteins.

Magnetic Bead Enzyme-Linked Immunosorbent Assay (ELISA) Detects Antigen-Specific Binding by Phage-Displayed scFv Antibodies That Are Not Detected with Conventional ELISA

An efficient means for the detection of antigen-specific binding by phage-displayed antibodies would facilitate the selection of such phage, especially from libraries with large repertoires of V-genes. We report the development and characterization of a magnetic bead phage ELISA which detects antigen binding phage which could not be detected by conventional ELISA. We were attempting to select phage binding to the oncodevelopmental antigen, heat-stable alkaline phosphatase (HSAP). Although there was an obvious enrichment in the phage titers after successive rounds of selection, we were unable to detect antigen-binding phage by ELISA on a plastic surface. However, ELISA with a suspension of superparamagnetic particles covalently conjugated to HSAP effectively identified antigen-binding phage after the fourth round of selection. This method could also detect antigen-specific binding of individual phage clones. Some of the phage clones bound to either amino- or carboxy-terminal-conjugated HSAP, perhaps reflecting the differences in the exposed epitopes. It is suggested that a sensitive method such as magnetic bead phage ELISA be tried before declaring a phage selection as unsuccessful or concluding that a phage clone does not bind antigen.

Mutational Analysis of Thrombopoietin for Identification of Receptor and Neutralizing Antibody Sites

Thrombopoietin (TPO) is a hematopoietin important for megakaryocyte proliferation and production of blood platelets. We sought to characterize how TPO binds and activates its receptor, myeloproliferative leukemia virus receptor. The erythropoietin-like domain of TPO (TPO1-153) has been fused to the gIII coat protein of M13 bacteriophage. Forty residues were chosen for mutation to alanine using the criteria that they were charged residues or predicted to be solvent-exposed, based on a homology model. Phage enzyme-linked immunosorbent assay was used to determine affinities for binding to both the TPO receptor and five anti-TPO1-153 monoclonal antibodies. Mutations at mostly positively charged residues (Asp8, Lys14, Lys52, Lys59, Lys136, Lys138, Arg140) caused the greatest reduction in receptor-binding affinity. Most of these residues mapped to helices-1 and -4 and a loop region between helix-1 and helix-2. Two of the monoclonal antibodies that blocked TPO binding and bioactivity had determinants in helix-4. In contrast, the other three monoclonal antibodies, which were effective at blocking TPO activity but did not block initial binding of TPO to its receptor, had epitopes predominantly on helix or 3. These results suggest that TPO has two distinct receptor-binding sites that function to dimerize TPO receptors in a sequential fashion.

Monoclonal antibodies against a minor and the major coat proteins of filamentous phage M13: their application in phage display

We have produced monoclonal antibodies (MAbs) which react with a minor and the major coat proteins of filamentous phage M13 and have characterised them by combining the techniques of enzyme-linked immunosorbent assay (ELISA) and Western blotting. These coat proteins are the minor coat protein, gIIIp, the product of gene III and the major coat protein, gVIIIp, the product of gene VIII. Both gIIIp and gVIIIp are important in the context of ‘phage display’ of foreign peptides/proteins as fusions to these proteins. The anti-gIIIp MAbs were able to detect native gIIIp as well as the fusion proteins comprising foreign proteins and gIIIp in ELISA and on Western blot, indicating their utility for studying the expression of foreign proteins in phage display. Similarly anti-gVIIIp MAbs detected gVIIIp both in ELISA and on Western blot. In an ‘affinity capture phage ELISA’, phages that were captured by virtue of the interaction between the foreign protein (ligand fused to the gIIIp and displayed on the phage surface) and the immobilised counterpart (receptor), could be easily detected using anti-gVIIIp MAbs. Considering the potential of ‘phage display’ technology in protein engineering, these antibodies should find wide applications.