title: Functional expression and affinity selection of single-chain cro by phage display: isolation of novel DNA-binding proteins.
abstract: A robust selection system affording phage display of the DNA-binding helix-turn-helix protein Cro is presented. The aim of the work was to construct an experimental system allowing for the construction and isolation of Cro-derived protein with new DNA-binding properties. A derivative of the phage lambda Cro repressor, scCro8, in which the protein subunits had been covalently connected via a peptide linker was expressed in fusion with the gene 3 protein of Escherichia coli filamentous phage. The phage-displayed single-chain Cro was shown to retain the DNA binding properties of its wild-type Cro counterpart regarding DNA sequence specificity and binding affinity. A kinetic analysis revealed the rate constant of dissociation of the single-chain Cro-phage/DNA complex to be indistinguishable from that of the free single-chain Cro. Affinity selection using a biotinylated DNA with a target consensus operator sequence allowed for a 3000-fold enrichment of phages displaying single-chain Cro over control phages. The selection was based on entrapment of phage/DNA complexes formed in solution on streptavidin-coated paramagnetic beads. The expression system was subsequently used to isolate variant scCro8 proteins, mutated in their DNA-binding residues, that specifically recognized new, unnatural target DNA ligands.
authors.affiliation: Department of Biochemistry, Uppsala University, Biomedical Center, Box 576, SE-751 23 Uppsala, Sweden. mikael.widersten@biokem.uu.se
authors.forename: M T
authors.initials: MT
authors.lastname: Nilsson
authors.forename: M C
authors.initials: MC
authors.lastname: Mossing
authors.forename: M
authors.initials: M
authors.lastname: Widersten
mesh_terms: D010582:Bacteriophage lambda / Q000235:genetics*; D001483:Base Sequence; D019921:Biotinylation; D002846:Chromatography, Affinity; D016384:Consensus Sequence; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000302:isolation & purification* / Q000378:metabolism; D019077:Helix-Turn-Helix Motifs; D008969:Molecular Sequence Data; D009875:Operator Regions, Genetic; D019151:Peptide Library; D016133:Polymerase Chain Reaction; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D013379:Substrate Specificity; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins
chemical_list: D004268:DNA-Binding Proteins; D019151:Peptide Library; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins; C016649:phage repressor proteins; D004247:DNA