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Publication Abstract from PubMed

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.

An affibody in complex with a target protein: structure and coupled folding.,Wahlberg E, Lendel C, Helgstrand M, Allard P, Dincbas-Renqvist V, Hedqvist A, Berglund H, Nygren PA, Hard T Proc Natl Acad Sci U S A. 2003 Mar 18;100(6):3185-90. Epub 2003 Feb 19. PMID:12594333^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.