GENE SYNTHESIS AND FUNCTIONAL EXPRESSION OF A PROTEIN EXHIBITING MONODOMAIN IGG FC BINDING

A gene encoding a bacterial IgG Fc binding domain was designed and syn thesized. The synthetic DNA fragment was cloned 3' to an inducible trp E promoter such that expression of the gene in Escherichia coli produc ed abundant Fc binding protein fused to the first seven amino acids of the trpE protein. The recombinant protein contained a single Fc bindi ng domain and demonstrated efficient binding to human IgG in Western b lot analysis. This protein degraded rapidly following cell lysis in th e absence of protease inhibitors, but could be effectively protected b y the addition of protease inhibitor. After purification of the protei n by IgG affinity chromatography, IgG Fc binding ability was retained for at least 24 h at either 23 or 37 degrees C and on heating for 15 m in at temperatures up to 65 degrees C. No immunoprecipitation was obse rved in interactions between the monodomain Fc binding protein and IgG molecules. Unlike staphylococcal protein A, no detectable binding of the monodomain IgG Fc binding protein was observed to either IgM or Ig A. Truncated proteins, expressed from a series of 3' deletions of the synthetic gene, were used to estimate the minimum portion of a monodom ain Fc binding protein that retained Fc binding ability.