Novel high-affinity binders of human interferon gamma derived from albumin-binding domain of protein G

Recombinant ligands derived from small protein scaffolds show promise as robust research and diagnostic reagents and next generation protein therapeutics. Here, we derived high-affinity binders of human interferon gamma (hIFN gamma) from the three helix bundle scaffold of the albumin-binding domain (ABD) of protein G from Streptococcus G148. Computational interaction energy mapping, solvent accessibility assessment, and in silico alanine scanning identified 11 residues from the albumin-binding surface of ABD as suitable for randomization. A corresponding combinatorial ABD scaffold library was synthesized and screened for hIFN gamma binders using in vitro ribosome display selection, to yield recombinant ligands that exhibited Kd values for hIFN gamma from 0.2 to 10 nM. Molecular modeling, computational docking onto hIFN gamma, and in vitro competition for hIFN gamma binding revealed that four of the best ABD-derived ligands shared a common binding surface on hIFN gamma, which differed from the site of human IFN gamma receptor 1 binding. Thus, these hIFN gamma ligands provide a proof of concept for design of novel recombinant binding proteins derived from the ABD scaffold. Proteins 2011. (C) 2012 Wiley Periodicals, Inc.