title: Engineering of a femtomolar affinity binding protein to human serum albumin.
abstract: We describe the development of a novel serum albumin binding protein showing an extremely high affinity (K(D)) for HSA in the femtomolar range. Using a naturally occurring 46-residue three-helix bundle albumin binding domain (ABD) of nanomolar affinity for HSA as template, 15 residues were targeted for a combinatorial protein engineering strategy to identify variants showing improved HSA affinities. Sequencing of 55 unique phage display-selected clones showed a strong bias for wild-type residues at nine positions, whereas various changes were observed at other positions, including charge shifts. Additionally, a few non-designed substitutions appeared. On the basis of the sequences of 12 variants showing high overall binding affinities and slow dissociation rate kinetics, a set of seven 'second generation' variants were constructed. One variant denoted ABD035 displaying wild-type-like secondary structure content and excellent thermal denaturation/renaturation properties showed an apparent affinity for HSA in the range of 50-500 fM, corresponding to several orders of magnitude improvement compared with the wild-type domain. The ABD035 variant also showed an improved affinity toward serum albumin from a number of other species, and a capture experiment involving human serum indicated that the selectivity for serum albumin had not been compromised from the affinity engineering.
authors.affiliation: Affibody AB, Voltavägen 13, SE-161 02 Bromma.
authors.forename: Andreas
authors.initials: A
authors.lastname: Jonsson
authors.forename: Jakob
authors.initials: J
authors.lastname: Dogan
authors.forename: Nina
authors.initials: N
authors.lastname: Herne
authors.forename: Lars
authors.initials: L
authors.lastname: Abrahmsén
authors.forename: Per-Ake
authors.initials: PA
authors.lastname: Nygren
mesh_terms: D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D019151:Peptide Library; D015202:Protein Engineering / Q000379:methods*; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012709:Serum Albumin / Q000737:chemistry / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D019151:Peptide Library; D011994:Recombinant Proteins; D012709:Serum Albumin