Structure and sequence data.

<p>(<b>A</b>): Computer graphic representation of a part of the complex between a single staphylococcal protein A domain (domain B, closely related to the Z domain used in the present study) (yellow) and human IgG₁ Fc (brown) (PDB file: 1FC2.pdb). The amino acid side chains corresponding to the seven positions addressed for substitutions in the Z domain are highlighted in cyan. Highlighted in purple, red and green, respectively, are three IgG1 Fc subregions in close contact with the B domain. (<b>B</b>): Alignment of amino acid sequences of Fc regions of human IgG₁, mouse IgG₁, mouse IgG_2a and mouse IgG_2b, respectively, corresponding to the three contact areas shown in (A), using the same colour code. (<b>C</b>): Amino acid sequence of the 58-residue Z domain, with the seven positions included in the engineering boxed. Indicated with red dots are the ten positions at which unique cysteine residues were introduced for site-specific labeling with a photoactivable maleimide benzophenone (MBP) group.