title: Functional folding of a cytoplasmic single-chain variable fragment and its use as elutable protein purification tag.
abstract: The variable fragment (Fv) of the monoclonal B1-8 antibody recognizes 3-nitro-4-hydroxy-phenylacetate (NP) and 5-iodo-NP (NIP) allowing for the affinity purification of the respective B cell antigen receptor with NP-sepharose and its specific elution with NIP-capronic acid (NIPcap). We generated an intracellular single-chain B1-8 Fv (iscFv), fused it to the N-terminus of the regulatory subunit (p85alpha) of phosphatidylinositol-3-kinase (PI3K) (isc-p85alpha), and examined the potential of this iscFv to serve as an intracellular elutable protein purification tag. The isc-p85alpha fusion protein could be specifically affinity-purified from the lysates of transfected Drosophila S2 cells with NP-sepharose and eluted with NIPcap, indicating the functional folding of the iscFv in the reducing environment of the cytosol. Furthermore, co-purification of the catalytic subunit of PI3K (p110) was achieved from lysates of co-transfected S2 cells as well as RBL-2H3 mast cells stably expressing isc-p85alpha. This indicates that the iscFv part of isc-p85alpha does not negatively influence p85alpha folding and interaction with p110. Moreover, successful incorporation of the p85alpha-moiety of isc-p85alpha into endogenous protein complexes in mast cells suggests the use of isc-containing fusion proteins for the native purification, elution, and analysis of intracellular signaling complexes.
authors.affiliation: Department of Molecular Immunology, Biology III, University of Freiburg, Freiburg, Germany.
authors.forename: Winfried
authors.initials: W
authors.lastname: Elis
authors.forename: Michael
authors.initials: M
authors.lastname: Reth
authors.forename: Michael
authors.initials: M
authors.lastname: Huber
mesh_terms: D000818:Animals; D002417:Cattle; D004331:Drosophila melanogaster / Q000276:immunology; D007128:Immunoglobulin Fragments / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D007135:Immunoglobulin Variable Region / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D017510:Protein Folding; D011947:Receptors, Antigen, B-Cell / Q000302:isolation & purification*; D011993:Recombinant Fusion Proteins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology
chemical_list: D007128:Immunoglobulin Fragments; D007135:Immunoglobulin Variable Region; D011947:Receptors, Antigen, B-Cell; D011993:Recombinant Fusion Proteins