Recombinant Mouse G6b Fc Chimera Protein

G6b is a type I transmembrane glycoprotein in the immunoglobulin superfamily that is encoded within the human class III major histocompatibility complex (1‑3). It is expressed mainly on platelets, and has also been detected on megakaryocytes and the human cell line K562 (2‑5). Crosslinking of G6b inhibits agonist‑stimulated platelet aggregation and activation (5). The 242 amino acid (aa) mouse G6b (equivalent to human G6b‑B) contains a 17 aa signal sequence, a 123 aa extracellular domain with one V‑type Ig‑like domain and one predicted N‑linked glycosylation site, a 21 aa transmembrane sequence and an 81 aa cytoplasmic sequence with two ITIM inhibitory motifs and an SH3 binding site (1, 2). Phosphorylation at the human equivalent of mouse Y212 within the first ITIM is required for interaction with SHP adaptor/tyrosine phosphatase proteins (2, 3). Of several described human isoforms, all are identical within aa 22‑136, which includes most of the extracellular domain. The one described mouse isoform is the equivalent of human G6b‑A, a transmembrane form with an alternate C‑terminus that lacks the ITIM motifs.  Since the ITIM motifs are required for G6b inhibition of GPIV and CLEC‑2 signals, it is possible that the G6b‑A isoform may be paired with and control inhibition by G6b (4, 6). Heparin interacts with the G6b extracellular domain with high‑affinity and may contribute to G6b activity or adhesion to extracellular matrix (7).