A SLe(x)-type proteoglycan, which through high affinity, calcium-dependent interactions with E- and P-selectins, mediates rapid rolling of leukocytes over vascular surfaces during the initial steps in inflammation. Critical for the initial leukocyte capture. Homodimer; disulfide-linked. Interacts with P- and E-selectins, through their lectin/EGF domains. Interaction with P-selectin requires sialyl Lewis X glycan modification and tyrosine sulfation, probably on Tyr-54, for high affinity binding (By similarity). Dimerization appears not to be required for P-selectin/SELP binding (By similarity). Interacts with SNX20 (By similarity). Interacts with MSN and SYK; mediates SYK activation downstream of SELPLG (By similarity). Interacts with HAVCR1 (By similarity). Highly expressed in blood, bone marrow, brain, adipose tissue, spleen, and thymus. Also expressed in heart, kidney, liver, muscle, ovary, and stomach. Displays complex, core-2, sialylated and fucosylated O-linked oligosaccharides, at least some of which appear to contain poly-N-acetyllactosamine with varying degrees of substitution. Mainly disialylated or neutral forms of the core-2 tetrasaccharide, Galbeta1-->4GlcNAcbeta1-->6(Galbeta1-->3)GalNAcOH. The GlcN:GalN ratio is approximately 2:1 and the Man:Fuc ratio 3:5. Contains about 14% fucose with alpha-1,3 linkage present in two forms: One species is a disialylated, monofucosylated glycan, and the other, a monosialylated, trifucosylated glycan with a polylactosamine backbone. The fucosylated forms carry the Lewis antigen and are important for interaction with selectins and for functioning. No sulfated O-glycans. Some N-glycosylation (By similarity).