title: Selection, characterization, and CDR shuffling of naive llama single-domain antibodies selected against auxin and their cross-reactivity with auxinic herbicides from four chemical families.
abstract: Indoleacetic acid (IAA)-binding single-domain antibodies (sdAbs) were isolated from a naive phage-display library constructed from the heavy chain antibody repertoire of a Ilama. The highest-affinity sdAb isolated (CSF2A) had a K(D) of 5-20 microM for two IAA-protein conjugates and a K(D) of 20 microM for free IAA. This sdAb also bound to a synthetic auxin analogue, 1-naphthaleneacetic acid (NAA), and to six auxinic herbicides (K(D) values of 0.5-2 mM), but not to serotonin and tryptophan, which are structurally similar to IAA but have no auxinic activity. To understand how sdAb CSF2A binds IAA and to determine which complementary-determining region(s) (CDR) participate(s) most in binding IAA, CSF2A was shuffled with four other sdAb clones by staggered extension process (StEP). After panning against IAA, two shuffled sdAbs were found: sdAb CSB1A, which originated from three different parental clones, and sdAb CSE8A, derived from two parental clones. These shuffled sdAbs and CSF2A were each fused to the B subunit of the Escherichia coli verotoxin, resulting in the formation of the pentamerized sdAbs V2NCSB1A, V2NCSE8A, and V2NCSF2A, which were analyzed by surface plasmon resonance (SPR) along with the sdAbs previously isolated. The shuffled clones had affinity for IAA (20 microM) similar to that of the highest affinity parental clone CSF2A, but much lower affinity for the auxinic herbicides. CDR2 was instrumental in binding IAA, whereas hydrophobic CDR3 was important for binding the auxinic herbicides. A novel SPR methodology is also described for specific immobilization of pentamerized sdAbs, allowing determination of K(D) values of Ab interaction with underivatized, low molecular weight haptens.
authors.affiliation: Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada.
authors.forename: Claudia
authors.initials: C
authors.lastname: Sheedy
authors.forename: Kerrm Y F
authors.initials: KY
authors.lastname: Yau
authors.forename: Tomoko
authors.initials: T
authors.lastname: Hirama
authors.forename: C Roger
authors.initials: CR
authors.lastname: MacKenzie
authors.forename: J Christopher
authors.initials: JC
authors.lastname: Hall
mesh_terms: D000818:Animals; D000906:Antibodies / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D000937:Antigen-Antibody Reactions; D001483:Base Sequence; D002161:Camelids, New World / Q000276:immunology*; D022801:Complementarity Determining Regions; D003429:Cross Reactions; D015723:Gene Library; D006241:Haptens; D006540:Herbicides / Q000276:immunology; D007210:Indoleacetic Acids / Q000737:chemistry / Q000276:immunology*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D016133:Polymerase Chain Reaction / Q000379:methods; D016415:Sequence Alignment; D020349:Surface Plasmon Resonance / Q000379:methods
chemical_list: D000906:Antibodies; D022801:Complementarity Determining Regions; D006241:Haptens; D006540:Herbicides; D007210:Indoleacetic Acids; C030737:indoleacetic acid