Immunoaffinity purification and characterization of RNA polymerase from Shewanella oneidensis

Novel polyol-responsive monoclonal antibodies against extracellular β-D-glucans from Pleurotus ostreatus

β-D-glucans from mushroom strains play a major role as biological response modifiers in several clinical disorders. Therefore, a specific assay method is of critical importance to find useful and novel sources of β-d-glucans with anti-tumor activity. Hybridoma technology was used to raise monoclonal antibodies (Mabs) against extracellular β-d-glucans (EBG) from Pleurotus ostreatus. Two of these hybridoma clones (3F8_3H7 and 1E6_1E8_B3) secreting Mabs against EBG from P. ostreatus were selected and 3F8_3H7 was used to investigate if they are polyol-responsive Mabs (PR-Mabs) by using ELlSA-elution assay. This hybridoma cell line secreted Mab of IgM class, which was purified in a single step by gel filtration chromatography on Sephacryl S-300HR, which revealed a protein band on native PAGE with Mr of 917 kDa. Specificity studies of Mab 3F8_3H7 revealed that it recognized a common epitope on several β-d-glucans from different basidiomycete strains as determined by indirect ELlSA and Western blotting under native conditions. This Mab exhibited high apparent affinity constant (KApp) for β-d-glucans from several mushroom strains. However, it revealed differential reactivity to some heat-treated β-d-glucans compared with the native forms suggesting that it binds to a conformation-sensitive epitope on β-d-glucan molecule. Epitope analysis of Mab 3F8_3H7 and 1E6_1E8_B3 was investigated by additivity index parameter, which revealed that they bound to the same epitope on some β-d-glucans and to different epitopes in other antigens. Therefore, these Mab can be used to assay for β-d-glucans as well as to act as powerful probes to detect conformational changes in these biopolymers.

Challenges and opportunities in the purification of recombinant tagged proteins

The purification of recombinant proteins by affinity chromatography is one of the most efficient strategies due to the high recovery yields and purity achieved. However, this is dependent on the availability of specific affinity adsorbents for each particular target protein. The diversity of proteins to be purified augments the complexity and number of specific affinity adsorbents needed, and therefore generic platforms for the purification of recombinant proteins are appealing strategies. This justifies why genetically encoded affinity tags became so popular for recombinant protein purification, as these systems only require specific ligands for the capture of the fusion protein through a pre-defined affinity tag tail. There is a wide range of available affinity pairs "tag-ligand" combining biological or structural affinity ligands with the respective binding tags. This review gives a general overview of the well-established "tag-ligand" systems available for fusion protein purification and also explores current unconventional strategies under development.

The epitope for the polyol-responsive monoclonal antibody 8RB13 is in the flap-domain of the beta-subunit of bacterial RNA polymerase and can be used as an epitope tag for immunoaffinity chromatography

Polyol-responsive monoclonal antibodies (PR-mAbs) are useful for the purification of proteins in an easy, one step immunoaffinity step. These antibodies allow for gentle purification of proteins and protein complexes using a combination of a low molecular weight polyhydroxylated compound (polyol) and a nonchaotrophic salt in the eluting buffer. mAb 8RB13 has been characterized as one of these PR-mAbs and has been used to purify RNA polymerase from five species of bacteria. Here the epitope for 8RB13 has been identified as PEEKLLRAIFGEKAS, a sequence that is highly conserved in the β-subunit of bacterial RNA polymerase. This sequence is located in the "beta-flap" domain of RNA polymerase (and essentially comprises the "flap-tip helix"), an important binding site for sigma70. This location explains why only the core RNAP is purified using this mAb. This amino acid sequence has been developed into an epitope tag that can be used to purify a target protein from either bacterial or eukaryotic cells when genetically fused to a protein of interest.

Identification, production, and use of polyol-responsive monoclonal antibodies for immunoaffinity chromatography

Immunoaffinity chromatography is a powerful tool for purification of proteins and protein complexes. The availability of monoclonal antibodies (mAbs) has revolutionized the field of immunoaffinity chromatography by providing a continuous supply of highly uniform antibody. Before the availability of mAbs, the recovery of the target protein from immobilized polyclonal antibodies usually required very harsh, often denaturing conditions. Although harsh conditions are often still used to disrupt the antigen-antibody interaction when using a mAb, various methods have been developed to exploit the uniformity of the antigen-antibody reaction in order to identify agents or conditions that gently disrupt this interaction and thus result in higher recovery of active protein from immunoaffinity chromatography. We discuss here the use of a specific type of monoclonal antibody that we have designated "polyol-responsive monoclonal antibodies" (PR-mAbs). These are naturally occurring mAbs that have high affinity for the antigen under binding conditions, but have low affinity in the presence of a combination of low molecular weight hydroxylated compounds (polyols) and nonchaotropic salts. Therefore, these PR-mAbs can be used for gentle immunoaffinity chromatography. PR-mAbs can be easily identified and adapted to a powerful protein purification method for a target protein.

In vivo assembly and single-molecule characterization of the transcription machinery from Shewanella oneidensis MR-1

Harnessing the new bioremediation and biotechnology applications offered by the dissimilatory metal-reducing bacteria, Shewanella oneidensis MR-1, requires a clear understanding of its transcription machinery, a pivotal component in maintaining vitality and in responding to various conditions, including starvation and environmental stress. Here, we have reconstituted the S. oneidensis RNA polymerase (RNAP) core in vivo by generating a co-overexpression construct that produces a long polycistronic mRNA encoding all of the core subunits (alpha, beta, beta', and omega) and verified that this reconstituted core is capable of forming fully functional holoenzymes with the S. oneidensis sigma factors sigma(70), sigma(38), sigma(32), and sigma(24). Further, to demonstrate the applications for this reconstituted core, we report the application of single-molecule fluorescence resonance energy transfer (smFRET) assays to monitor the mechanisms of transcription by the S. oneidensis sigma(70)-RNAP holoenyzme. These results show that the reconstituted transcription machinery from S. oneidensis, like its Escherichia coli counterpart, "scrunches" the DNA into its active center during initial transcription, and that as the holoenzyme transitions into elongation, the release of sigma(70) is non-obligatory.