Structural characterization of a recombinant CD4‐IgG hybrid molecule

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Abstract
CD4‐IgG is a homodimer of a hybrid polypeptide consisting of the two amino‐terminal domains (residues 1–180) of human CD4 fused to the hinge region and the second and third constant‐sequence (CH2 and CH3) Fc domains (residues 216–441) of human immunoglobulin G (IgG‐1). This antibody‐like molecule, termed an immunoadhesin, was produced in an effort to combine the binding specificity of CD4 with several potentially desirable properties of IgG molecules [Capon et al. (1989) Nature 337, 525–531]. The structural characteristics of the molecule have been evaluated to demonstrate that CD4‐IgG has the same features as the N‐terminal region of soluble CD4, while retaining those expected for the Fc portion of human IgG. Identification of peptides recovered from the tryptic map confirmed 98.8% of the expected structure of CD4‐IgG. The detection of glucosamine in peptides containing Asn257 and the retention time shift of this tryptic peptide after deglycosylation confirmed the presence of Asn‐linked oligosaccharides at this position. Four pairs of intrachain and two interchain disulfide bonds were also established.