Description
Heregulin (HRG) is a glycoprotein of 44kDa which binds to c-erbB-3 and c-erbB-4 receptors with low and high affinities, respectively. Heregulins constitute a family of mosaic proteins comprising of at least 12 members. They contain certain recognizable domains which include: an amino terminal (N-ter) region; an immunoglobulinlike motif (Ig); a glycosylated spacer sequence (glyco); an EGF-like motif (EGF), which is subdivided into α and β isoforms; a juxtamembrane region subdivided into isoforms 1-3; a hydrophobic transmembrane domain (TM); a common cytoplasmic tail (Cyto); and a variable-length cytoplasmic tail (a-c). Using this nomenclature, several isoforms of HRG are designated as HRG-α1, HRG-α2, HRG-α3, HRG-β1, HRG-β2, HRG-β3, HRG-α2b, etc