Epitopes of Escherichia coli ribosomal protein S13

A monoclonal antibody reacts with maltose-binding protein of Escherichia coli and related enteric bacteria

Maltose-binding protein (MBP) encoded by malE is essential for the energy-dependent translocation of maltose through the cytoplasmic membrane of bacteria. Its property of specific binding to maltose has been used in constructing fusion proteins for easy affinity purification. A monoclonal antibody named MAb SC1D7 was produced against Escherichia coli MBP. This MAb also bound to MBP-containing recombinant proteins in both Western blotting and immunoprecipitation analysis. As a result, this MAb can be a useful probe for tracing MBP-fusion proteins in various applications. Furthermore, intrinsic MBPs from E. coli, Shigella dysenteriae, Salmonella typhimurium, Enterobacter cloacae, and Klebsiella pneumoniae were also detected by this MAb. No reaction was observed with the total proteins from Serratia marcescens, Aeromonas hydrophila and Plesiomonas shigelloides. These observations suggest that the MAb SC1D7-defined epitope is conserved among some enteric bacteria, but not the others. The results strengthen the phylogenetic positions of these closely related bacteria previously placed by other means.

Characterization of monoclonal antibodies to the 26-kDa glutathione S-transferase of Schistosoma japonicum

Six monoclonal antibodies (MAbs) were raised in mice against the 26-kDa glutathione S-transferase (GST) of the parasite Schistosoma japonicum. These MAbs were originally selected for their specific binding to the recombinant GST (r-GST) generated in E. coli by an enzyme-linked immunosorbent assay. A further study demonstrated that all these MAbs bound to plate-coated GST affinity-purified from the parasite Schistosoma japonicum. However, in Western blotting analysis only a single monoclonal antibody (MAb Y3D7) yielded positive binding. The binding of MAb Y3D7 on Western blotting was further characterized; specific binding was found on other GST fusion proteins and on the authentic 26-kDa GST but not the 28-kDa GST in the total soluble worm proteins from Schistosoma japonicum. Using protein-A-mediated immunoprecipitation, MAbs Y3D7 and Y5D5 precipitated r-GST while in parallel experiments the remaining MAbs did not generate r-GST precipitation. In an alternative co-precipitation experiment, r-GST was first bound to glutathione (GSH) Sepharose beads and subsequently tested for interaction with the MAbs. In this manner, all MAbs except MAb Y5D5 were co-precipitated with the complexes. Thus, these select MAbs readily reacted with GST although their binding characteristics were different. Because GST has been widely used in the generation of fusion proteins for various purposes and is a potential vaccine candidate in controlling schistosomiasis, these MAbs should prove valuable for their application to molecular biology and parasitology.

Epitopic analysis and quantification of bovine myoglobin with monoclonal antibodies

Seven rat monoclonal antibodies (MAb) for bovine myoglobin were produced. Five antibodies reacted with surface-absorbed myoglobin whereas the two remainders reacted only in a sandwich type ELISA. The ability of different antibodies to bind simultaneously to myoglobin was examined by competition and additivity experiments and three noncompeting epitope regions were found. A two-site enzyme immunoassay was developed and allowed quantification of 30 ng/ml bovine myoglobin. These antibodies should be valuable tools in comparative studies for immunological reactivity of mammalian myoglobins and for myoglobin measurement in serum and urine of myopathic animals.

Both ends of Escherichia coli ribosomal protein S13 are immunochemically accessible in situ

To investigate the structure of Escherichia coli ribosomal protein S13 in 30S ribosomal subunits, we have previously generated 22 S13 specific monoclonal antibodies and mapped their specific epitopes to the S13 sequence. The availability of these S13 epitopes in situ has been further examined by incubating these monoclonal antibodies with 30S ribosomal subunits and analyzing formation of monoclonal antibody-linked ribosome dimers by sucrose gradients centrifugation. We have found that none of the 22 monoclonal antibodies makes ribosome dimers individually as do typical antisera. However, one monoclonal antibody, designated AS13-MAb 2, reacts with 30S ribosomal subunits to form immunocomplexes sedimenting faster than subunit monomers. When AS13-MAb 2 is paired with any one of three monoclonal antibodies directed to the S13 C-terminal epitopes, dimer formation is observed. Other pairs of monoclonal antibodies directed to distinct S13 epitopes have been tested similarly for dimer formation. Monoclonal antibody AS13-MAb 22, directed to the N-terminal region of 22 residues, also causes subunits to form typical dimers, but only if paired with one of the three monoclonal antibodies directed to the S13 C-terminal region. The close proximity of the epitopes recognized by AS13-MAbs 2 and 22 has been established by the mutual competition between the antibodies binding to intact 30S subunits. These results corroborate our previous observation, using polyclonal antibodies, that S13 has more than one epitope exposed on 30S subunits. Our finding that sequences on both ends of the S13 molecule are immunochemically accessible provides information about the molecular organization of S13 in situ.

Detecting immunocomplex formation in sucrose gradients by enzyme immunoassay: application in determining epitope accessibility on ribosomes

A sensitive method using enzyme immunoassay and sucrose gradient to analyze immunocomplexes of biological particles has been developed. The sensitivity and application of this method were demonstrated by that the in situ accessibility of ribosomal protein epitopes could be easily determined. We used sucrose gradients to separate the ribosome-bound and the free antibodies and traced the antibodies in the gradients by an enzyme-linked immunosorbent assay. Epitopes exposed in situ are bound by specific antibodies, which in turn are detected in sucrose gradients migrating with ribosomes. This method of detecting antibody migration is more sensitive than the conventional means of using A260nm to monitor the antibody-mediated dimerization of ribosomes. Furthermore, an epitope defined by a biotin-labeled monoclonal antibody can be analyzed in the presence of other unlabeled antibodies. Thus, the relationship of different accessible epitopes in situ can be readily examined. Versatility and sensitivity of this method should make it useful in analyzing a variety of immunocomplex systems.

Epitope mapping of monoclonal antibodies to Escherichia coli ribosomal protein S3

The antigenic structure of Escherichia coli ribosomal protein S3 has been investigated by use of monoclonal antibodies. Six S3-specific monoclonal antibodies secreted by mouse hybridomas have been identified by immunoblotting of two-dimensional ribosomal protein separation gels. By using a competitive enzyme-linked immunosorbent assay, we have divided these monoclonal antibodies into three mutual inhibition groups, members of which are directed to three distinct regions of the S3 molecule. The independence of these monoclonal antibody-defined regions was confirmed by the failure of pairs of monoclonal antibodies from two inhibition groups to block the binding of biotinylated monoclonal antibodies of the third group. To determine the regions recognized by these monoclonal antibodies, chemically cleaved S3 peptides were fractionated by gel filtration and reverse-phase high-performance liquid chromatography. The fractionated peptides were coated on plates and examined for specific interaction with monoclonal antibody by enzyme immunoassay. In this manner, two epitopes have been mapped at the ends of the S3 molecule: one, in the last 22 residues, is recognized by three monoclonal antibodies; and the second, in the first 21 residues, is defined by two monoclonal antibodies. The third S3 epitope, recognized by a single monoclonal antibody, has been localized in a central segment of about 90 residues by gel electrophoresis and immunoblotting. These epitope-mapped monoclonal antibodies are valuable probes for studying S3 structure in situ.