SHOT-GUN PHAGE DISPLAY MAPPING OF 2 STREPTOCOCCAL CELL-SURFACE PROTEINS

We have used a phage display shot-gun cloning technique to map the bin ding domains in two cell surface proteins from animal group C streptoc occi. The proteins, MAG and ZAG, have affinity for alpha(2)-macroglobu lin (alpha(2)M), serum albumin and IgG. In this work, parts of the clo ned i mag and zag genes were randomly cloned into a phagemid vector, a nd recombinant phages expressing alpha(2)-M- or albumin-binding activi ty were isolated through panning against immobilized alpha(2)M or albu min. Analysis of the clones revealed two distinct alpha(2)M-binding si tes in protein MAG and two slightly overlapping binding sites in prote in ZAG. The minimal albumin-binding domain in protein ZAG, as deduced from the affinity selected clones, consisted of 42 amino acids. These results show that the phage display shot-gun cloning is a rapid and co nvenient way to characterize the binding site(s) in receptor proteins without any prior knowledge of their number, size, and localization.