title: An affibody in complex with a target protein: structure and coupled folding.
abstract: Combinatorial protein engineering provides powerful means for functional selection of novel binding proteins. One class of engineered binding proteins, denoted affibodies, is based on the three-helix scaffold of the Z domain derived from staphylococcal protein A. The Z(SPA-1) affibody has been selected from a phage-displayed library as a binder to protein A. Z(SPA-1) also binds with micromolar affinity to its own ancestor, the Z domain. We have characterized the Z(SPA-1) affibody in its uncomplexed state and determined the solution structure of a Z:Z(SPA-1) protein-protein complex. Uncomplexed Z(SPA-1) behaves as an aggregation-prone molten globule, but folding occurs on binding, and the original (Z) three-helix bundle scaffold is fully formed in the complex. The structural basis for selection and strong binding is a large interaction interface with tight steric and polar/nonpolar complementarity that directly involves 10 of 13 mutated amino acid residues on Z(SPA-1). We also note similarities in how the surface of the Z domain responds by induced fit to binding of Z(SPA-1) and Ig Fc, respectively, suggesting that the Z(SPA-1) affibody is capable of mimicking the morphology of the natural binding partner for the Z domain.
authors.affiliation: Department of Biotechnology, Royal Institute of Technology, S-106 91 Stockholm, Sweden.
authors.forename: Elisabet
authors.initials: E
authors.lastname: Wahlberg
authors.forename: Christofer
authors.initials: C
authors.lastname: Lendel
authors.forename: Magnus
authors.initials: M
authors.lastname: Helgstrand
authors.forename: Peter
authors.initials: P
authors.lastname: Allard
authors.forename: Vildan
authors.initials: V
authors.lastname: Dincbas-Renqvist
authors.forename: Anders
authors.initials: A
authors.lastname: Hedqvist
authors.forename: Helena
authors.initials: H
authors.lastname: Berglund
authors.forename: Per-Ake
authors.initials: PA
authors.lastname: Nygren
authors.forename: Torleif
authors.initials: T
authors.lastname: Härd
mesh_terms: D000906:Antibodies / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D019151:Peptide Library; D015202:Protein Engineering; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013205:Staphylococcal Protein A / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D000906:Antibodies; D002352:Carrier Proteins; D046911:Macromolecular Substances; D019151:Peptide Library; D011994:Recombinant Proteins; D013205:Staphylococcal Protein A