First immunoglobulin (Ig)-like domain of Fcgamma-receptors (FcgammaRs), and similar domains
The members here are composed of the first immunoglobulin (Ig)-like domain of Fcgamma-receptors (FcgammaRs). Interactions between IgG and FcgammaR are important to the initiation of cellular and humoral response. IgG binding to FcgammaR leads to a cascade of signals and ultimately to functions such as antibody-dependent-cellular-cytotoxicity (ADCC), endocytosis, phagocytosis, release of inflammatory mediators, etc. FcgammaR has two Ig-like domains. This group also contains FcepsilonRI which binds IgE with high affinity.
Feature 1:pentraxin binding site [polypeptide binding site]
Evidence:
Structure:3D5O; human FcgammaRIIa first Ig domain interacts with serum amyloid P component (SAP), forming contacts with three chains of the SAP pentamer. Site defined using 4.0 A contacts.
Comment:Pentraxins, including SAP, are ancient conserved mediators of innate immunity that have been determined to interact with FcgammaRs to activate leukocyte-mediated phagocytosis.
Comment:Note that the pentameric SAP forms contacts with different but overlapping sets of residues in the first and second Ig domains of FcgammaRIIa. The first Ig domain forms contacts with three of the five SAP chains, while the second Ig domain forms contacts with two SAP chains.
Jiyao W et al.(2023). "The conserved domain database in 2023.",