ABSTRACT
The ability of a new class of metal binding tags to facilitate the purification of recombinant proteins, exemplified by the tagged glutathione S-transferase and human growth hormone, from Escherichia coli fermentation broths and lysates has been further investigated. These histidine-containing tags exhibit high affinity for borderline metal ions chelated to the immobilised ligand, 1,4,7-triazacyclononane (tacn). The use of this tag-tacn immobilised metal ion affinity chromatography (IMAC) system engenders high selectivity with regard to host cell protein removal and permits facile tag removal from the E. coli-expressed recombinant protein. In particular, these tags were specifically designed to enable their efficient removal by the dipeptidyl aminopeptidase 1 (DAP-1), thus capturing the advantages of high substrate specificity and rates of cleavage. MALDI-TOF MS analysis of the cleaved products from the DAP-1 digestion of the recombinant N-terminally tagged proteins confirmed the complete removal of the tag within 4-12 h under mild experimental conditions. Overall, this study demonstrates that the use of tags specifically designed to target tacn-based IMAC resins offers a comprehensive and flexible approach for the purification of E. coli-expressed recombinant proteins, where complete removal of the tag is an essential prerequisite for subsequent application of the purified native proteins in studies aimed at delineating the molecular and cellular basis of specific biological processes.
Subject(s)
Chromatography, Affinity/methods , Expressed Sequence Tags/chemistry , Recombinant Proteins/isolation & purification , Aminopeptidases/chemistry , Animals , Escherichia coli/genetics , Genetic Vectors , Glutathione Transferase/chemistry , Glutathione Transferase/genetics , Glutathione Transferase/isolation & purification , Heterocyclic Compounds/chemistry , Human Growth Hormone/chemistry , Human Growth Hormone/genetics , Human Growth Hormone/isolation & purification , Humans , Ions/chemistry , Metals/chemistry , Protein Structure, Tertiary , Proteolysis , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Schistosoma japonicum , Spectrometry, Mass, Matrix-Assisted Laser Desorption-IonizationABSTRACT
In this study, a pyridine-based compound, 4'-terpyridinylsulfanylethylamine (4'-TerPSEA), has been employed as a ligand to purify via mixed-mode chromatographic procedures a humanised monoclonal antibody of the IgG1 sub-class directly from crude supernatants derived from cultured CHO cells. The antibody binding capacity, selectivity and reusability of the adsorbent, derived from the immobilisation of this ligand onto Sepharose FF™, were compared to a Protein A affinity resin. The chromatographic performance of this mixed mode adsorbent was similar to that shown by the Protein A-based adsorbent with this IgG1 mAb. In addition, the IgG1 mAb was able to bind to the immobilised 4'-TerPSEA under reducing conditions. Through the use of papain-digested IgG1 mAb, fractionated with both the 4'-TerPSEA and Protein A adsorbents, it was found that this IgG1 mAb preferentially bound to the immobilised 4'-TerPSEA Sepharose FF™ resin through its Fc region.
Subject(s)
2,2'-Dipyridyl/analogs & derivatives , Antibodies, Monoclonal, Humanized/isolation & purification , Antibodies, Monoclonal/isolation & purification , Cysteamine/analogs & derivatives , Immunoglobulin G/isolation & purification , Resins, Synthetic/chemistry , 2,2'-Dipyridyl/chemistry , Adsorption , Animals , CHO Cells , Chromatography, Liquid/methods , Cricetinae , Cricetulus , Cysteamine/chemistry , Ligands , Protein Binding , Pyridines/chemistry , Sepharose/chemistry , Staphylococcal Protein A/chemistryABSTRACT
In this study, integration of three discrete process aspects of the IMAC purification of Escherichia coli expressed recombinant proteins has been investigated. To this end, novel N-terminally tagged human growth hormone variants (tagged-vhGHs) have been expressed in E. coli by tank fermentation and captured directly from the cell lysate by a new IMAC approach. The chelating ligands used were 1,4,7-triaza-cyclononane (tacn) and bis(1,4,7-triazacyclononyl)-propane (dtnp) with copper(II) as the immobilised metal ion. The N-terminal tags were specifically selected for their potential to bind to these immobilised complexes and also for their ease of removal from the tagged protein by the dipeptidyl peptidase, DAP-1. Low levels of detergents in the binding buffer did not dramatically affect the purification, but increased concentrations of NaCl in the loading buffer improved the binding performance. The same IMAC systems, operated in the 'negative' adsorption chromatographic mode, could be used to obtain the purified mature human growth hormone variant, as assessed by MALDI-TOF and N-terminal sequencing studies, following removal of the affinity tag by the dipeptidyl peptidase 1. Western immunoblot analysis of the eluted fractions of both the tagged and de-tagged vhGH demonstrated significant clearance of E. coli host cell proteins (HCPs). Further, these IMAC resins can be used multiple times without the need for metal ion re-charging between runs. This study thus documents an integrated approach for the purification of specifically tagged recombinant proteins expressed in genetically modified E. coli.
Subject(s)
Escherichia coli/genetics , Fermentation , Human Growth Hormone/isolation & purification , Recombinant Proteins/isolation & purification , Chelating Agents/chemistry , Chelating Agents/metabolism , Gene Expression Regulation, Bacterial , Human Growth Hormone/chemistry , Human Growth Hormone/genetics , Humans , Recombinant Proteins/chemistry , Recombinant Proteins/geneticsABSTRACT
BACKGROUND: Glucosinolates, a group of nitrogen and sulfur containing compounds associated with plant-insect interactions, are produced by a number of important Brassicaceae crop species. In Arabidopsis the AOP2 gene plays a role in the secondary modification of aliphatic (methionine-derived) glucosinolates, namely the conversion of methylsulfinylalkyl glucosinolates to form alkenyl glucosinolates, and also influences aliphatic glucosinolate accumulation. RESULTS: This study characterises the primary structural variation in the coding sequences of the AOP2 gene and identifies three different AOP2 alleles based on polymorphisms in exon two. To help determine the regulatory mechanisms mediating AOP2 expression amongst accessions, AOP2 5' regulatory regions were also examined however no major differences were identified. Expression of the AOP2 gene was found to be most abundant in leaf and stem tissue and was also found to be light dependent, with a number of light regulatory elements identified in the promoter region of the gene. In addition, a study was undertaken to demonstrate that the Arabidopsis AOP2 gene product is functional in planta. The over-expression of a functional AOP2 allele was found to successfully convert the precursor methylsulfinyl alkyl glucosinolate into the alkenyl form. CONCLUSIONS: The expression of the AOP2 gene has been found to be influenced by light and is most highly expressed in the photosynthetic parts of the Arabidopsis plant. The level of AOP2 transcript decreases rapidly in the absence of light. AOP2 exists as at least three alleles in different Arabidopsis accessions and we have demonstrated that one of these, AOP2-2, is functionally able to convert methylsulfinyl glucosinolates into the alkenyl form. The demonstration of the in planta functionality of the Arabisopsis AOP2 gene is an important step in determining the feasibility of engineering glucosinolate profiles in food plants.
