Mill2 (MHC class I‑like located near the leukocyte receptor complex‑2) is an ~41 kDa glycosyl‑phosphatidylinositol (GPI)‑linked glycoprotein that is a member of the non‑classical MHC class I‑like family (1‑3). Mouse Mill2 cDNA encodes 340 amino acids (aa) that include a signal sequence, an MHC I domain containing alpha 1, alpha 2 and alpha 3 regions, and a GPI anchor sequence (1). A long form contains 15 aa inserted near the N‑terminus. Mature mouse Mill2 (short form) shares 74% aa sequence identity with rat Mill2 and approximately 61% aa identity with mouse Mill1. Human orthologs of Mill proteins have not been identified, although similarities in structure and sequence with human HFE and MICA/B have been noted (1, 4, 5). Mill2 is expressed on proliferating thymocytes, smooth muscle cells and fibroblasts in skin, bladder, uterus and colonic muscularis (5). Low expression is detected in many tumor cell lines (5). Mill proteins bind beta 2‑microglobulin (2). While Mill1 requires beta 2‑microglobulin for surface expression, the short form of Mill2 does not, and surface expression of the long form is higher in its presence (5). Mill proteins are unlikely to present peptides and do not bind to NKG2D (2, 5). Recombinant Mill2 has, however, shown pH‑dependent binding to TfR/CD71‑expressing immature cells in the B lymphocyte and erythrocyte lineages, as well as activated, proliferating splenic T and B cells and some cell lines (5).
| Uniprot | Mouse |
| Product By Gene ID | 4277 |
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