Immunoglobulin (Ig)-like domain in the polymeric Ig receptor (pIgR) and similar proteins
The members here are composed of the immunoglobulin (Ig)-like domain in the polymeric Ig receptor (pIgR) and similar proteins. pIgR delivers dimeric IgA and pentameric IgM to mucosal secretions. Polymeric immunoglobulin (pIgs) are the first defense against pathogens and toxins. IgA and IgM can form polymers via an 18-residue extension at their C-termini referred to as the tailpiece. pIgR transports pIgs across mucosal epithelia into mucosal secretions. Human pIgR is a glycosylated type I transmembrane protein, comprised of a 620-residue extracellular region, a 23-residue transmembrane region, and a 103-residue cytoplasmic tail. The extracellular region contains five domains that share sequence similarity with Ig variable (v) regions. This group also contains the Ig-like extracellular domains of other receptors such as NK cell receptor Nkp44 and myeloid receptors, among others.
Comment:Identified via mutation studies of the CDR1 region. Point mutations of these residues and others in the neighboring non-conserved CDR1 reduce or abolish binding to dIgA.
Comment:In addition to CDR1, the other two CDR loops appear to be involved in the interaction with antibody.
Jiyao W et al.(2023). "The conserved domain database in 2023.",