Essential for normal retinal maturation and development (By similarity). Acts as a retinal cell surface receptor for NXNL1 and plays an important role in NXNL1-mediated survival of retinal cone photoreceptors (PubMed:25957687). In association with glucose transporter SLC16A1/GLUT1 and NXNL1, promotes retinal cone survival by enhancing aerobic glycolysis and accelerating the entry of glucose into photoreceptors (PubMed:25957687). May act as a potent stimulator of IL6 secretion in multiple cell lines that include monocytes (PubMed:21620857). (Microbial infection) Erythrocyte receptor for P.falciparum RH5 which is essential for erythrocyte invasion by the merozoite stage of P.falciparum isolates 3D7 and Dd2. Signaling receptor for cyclophilins, essential for PPIA/CYPA and PPIB/CYPB-dependent signaling related to chemotaxis and adhesion of immune cells (PubMed:11943775, PubMed:11688976). Plays an important role in targeting monocarboxylate transporters SLC16A1/GLUT1, SLC16A11 and SLC16A12 to the plasma membrane (PubMed:17127621, PubMed:21778275, PubMed:28666119). Acts as a coreceptor for vascular endothelial growth factor receptor 2 (KDR/VEGFR2) in endothelial cells enhancing its VEGFA-mediated activation and downstream signaling (PubMed:25825981). Promotes angiogenesis through EPAS1/HIF2A-mediated up-regulation of VEGFA (isoform VEGF-165 and VEGF-121) and KDR/VEGFR2 in endothelial cells (PubMed:19837976). Plays a key role in regulating tumor growth, invasion, metastasis and neoangiogenesis by stimulating the production and release of extracellular matrix metalloproteinases and KDR/VEGFR2 by both tumor cells and stromal cells (fibroblasts and endothelial cells) (PubMed:12553375, PubMed:11992541, PubMed:15833850). (Microbial infection) Erythrocyte receptor for P.falciparum RH5 which is essential for erythrocyte invasion by the merozoite stage of P.falciparum isolates 3D7, Dd2, 7G8 and HB3 (PubMed:22080952, PubMed:26195724). Binding of P.falciparum RH5 results in BSG dimerization which triggers an increase in intracellular Ca(2+) in the erythrocyte (PubMed:28409866). This essential step leads to a rearrangement of the erythrocyte cytoskeleton required for the merozoite invasion (PubMed:28409866). (Microbial infection) Can facilitate human SARS coronavirus (SARS-CoV-1) infection via its interaction with virus-associated PPIA/CYPA. (Microbial infection) Can facilitate HIV-1 infection via its interaction with virus-associated PPIA/CYPA. (Microbial infection) First described as a receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), it is not required for SARS-CoV-2 infection. (Microbial infection) Acts as a receptor for measles virus. (Microbial infection) Promotes entry of pentamer-expressing human cytomegalovirus (HCMV) into epithelial and endothelial cells. Homooligomer (PubMed:19768682). Interacts with NXNL1 (PubMed:25957687). Interacts with SLC2A1 and SLC16A1/GLUT1 (By similarity). Interacts with XKR8; promoting its localization at the cell membrane (PubMed:27503893). (Microbial infection) Interacts with P.falciparum (isolate 3D7) RH5/PfRH5; the interaction is required for the invasion of the host erythrocytes by the parasite at the merozoite stage. Homooligomer (PubMed:18430721). Forms heterooligomers with isoform 3 (PubMed:21536654). Interacts with VEGFA and KDR/VEGFR2 (PubMed:25825981). Interacts with PPIA/CYPA (PubMed:11353871, PubMed:11943775, PubMed:15688292, PubMed:21245143). Interacts with PPIL2; regulates BSG transport to the cell membrane (PubMed:15946952). Interacts with SLC16A1/GLUT1 (PubMed:17127621). Interacts with SLC16A12 (PubMed:21778275). Interacts with SLC16A11 (PubMed:28666119). Interacts with AJAP1 (PubMed:17267690). Interacts with SLC1A3, ATP1B2, MAG and L1CAM (By similarity). Interacts with SLC16A3; interaction mediates SLC16A3 targeting to the plasma membrane. (Microbial infection) Interacts with P.falciparum (isolates 3D7 or 7G8) RH5/PfRH5; the interaction is required for the invasion of the host erythrocytes by the parasite at the merozoite stage. (Microbial infection) Does not interact with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike glycoprotein, even if previous works were based on a putative interaction. Forms heterooligomers with isoform 2. Identified by mass spectrometry in melanosome fractions from stage I to stage IV. Retina-specific (PubMed:25957687). Expressed in retinal cone photoreceptors (at protein level) (PubMed:25957687). Expressed in erythrocytes (at protein level) (PubMed:26195724, PubMed:28409866). Highly expressed in melanoma cell lines (at protein level) (PubMed:11992541). Highly expressed in the heart, kidney, skeletal muscle and testis (PubMed:21536654). Highly expressed in the bone marrow, fetal liver, lung, testis and thymus. Highly expressed in the bone marrow, fetal liver, lung, testis and thymus. N-glycosylated. N-glycosylated. N-glycosylated. Potential candidate for the development of parasite blood stage vaccines. In vitro and in vivo, neutralizing antibodies are capable of inhibiting merozoite invasion of host erythrocytes. Produced by alternative promoter usage. Produced by alternative promoter usage. Blood group antigen gene mutation database