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Table 1 Mutation positions for histidine-scanning library

From: Engineered protein A ligands, derived from a histidine-scanning library, facilitate the affinity purification of IgG under mild acidic conditions

Number 5 6 9 10 11 13 14 15 17 24 25 27 28 31 32 35 36
Aminoacid residue of wild type F N Q Q N F Y E L E E R N I Q K D
Distance (Å) 5.7 11 6.4 4.2 6.5 3.8 3.4 7.9 4.0 8.4 8.7 8.6 6.9 5.8 8.1 4.5 9.8
fSASA (%) 78 94 36 47 64 40 63 50 46 78 96 23 71 17 60 64 68
Mixed codon used in the library YWT MAY CAW CAW MAY YWT YAT SAW CWK SAW SAW CRY MAY MWT CAW MAW SAT
Substituted amino acids in the library H      H   H H H H    H   H  
Y H H H H Y H D Q D D H H N H N H
L      L   Q   Q Q    L   Q  
  1. Distance in the table indicates the length between the PAB residue and the nearest positively charged residue in IgG-Fc. fSASA indicates the extent of solvent exposure of the side chain in wild-type amino acid residues of PAB. The seventeen mutation positions finally selected were classified into two groups: (1) the PAB residues were located within 9 Å from the positively charged IgG-Fc residues and (2) the PAB residues were located between 9 and 11 Å from the IgG-Fc residues, and with a fractional solvent-accessible surface area (fSASA) ((fSASA) = (SASA) (native)/SASA (denatured)) value of more than 68%. The following abbreviations are used for mixed bases: R = (A or G), Y = (C or T), M = (A or C), K = (G or T), S = (G or C) and W = (A or T). Substituted amino acid residues in the library indicate non-wild-type residues encoded by a mixed codon.