Identification of the Linear Fc-Binding Site on the Bovine IgG1 Fc Receptor (boFcγRIII) Using Synthetic Peptides.

Simple Summary: Bovine IgG1 Fc receptor (boFcγRIII) is a homologue to human FcγRIII (CD16) that has two extracellular Ig-like domains and can bind bovine IgG1 with medium–low affinity. We identified the Fc-binding site as well as its key residues for IgG1 binding using synthetic peptides, which is located in the second extracellular domain of boFcγRIII. It provides new insights for the IgG–Fcγ interaction and FcγR-targeting drugs development. The bovine IgG1 Fc receptor (boFcγRIII) is a homologue to human FcγRIII (CD16) that binds bovine IgGI with medium–low affinity. In order to identify the Fc-binding site on the bovine IgG1 Fc receptor (boFcγRIII), peptides derived from the second extracellular domain (EC2) of boFcγRIII were synthesized and conjugated with the carrier protein. With a Dot-blot assay, the ability of the peptides to bind bovine IgG1 was determined, and the IgG1-binding peptide was also identified via truncation and mutation. The minimal peptide AQRVVN corresponding to the sequence 98–103 of boFcγRIII bound bovine IgG1 in Dot-blot, suggesting that it represents a linear ligand-binding site located in the putative A–B loop of the boFcγRIII EC2 domain. Mutation analysis of the peptide showed that the residues of Ala⁹⁸, Gln⁹⁹, Val¹⁰¹, Val¹⁰² and Asn¹⁰³ within the Fc-binding site are critical for IgG1 binding on boFcγRIII. The functional peptide identified in this paper is of great value to the IgG–Fc interaction study and FcR-targeting drug development. [ABSTRACT FROM AUTHOR]