Vitronectin is a cell adhesion and spreading factor found in serum and tissues. Vitronectin interact with glycosaminoglycans and proteoglycans. Is recognized by certain members of the integrin family and serves as a cell-to-substrate adhesion molecule. Inhibitor of the membrane-damaging effect of the terminal cytolytic complement pathway. Somatomedin-B is a growth hormone-dependent serum factor with protease-inhibiting activity. Exists in two forms: a single chain 75 kDa form (V75) and a clipped form composed of two chains (65 kDa and 10 kDa) (V65+V10) which are held together by a disulfide bond. Interacts with SERPINE1/PAI1, insulin and C1QBP. (Microbial infection) Interacts (via hemopexin repeat 2) with P.falciparum (isolate CDC / Honduras) SERA5 P47 (via C-terminus); may form heterotetramers of two VTN and SERA5 P47 heterodimers; the interaction may protect merozoites from phagocytosis by host monocytes; VTN glycosylation appears to be dispensable for the interaction. (Microbial infection) In P.falciparum-infected red blood cells, VTN internalization is detected at the early trophozoite stage (PubMed:29567995). Colocalizes with SERA5 at the schizont stage and with SERA5 P47 at the merozoite surface (PubMed:29567995). Expressed in the retina pigment epithelium (at protein level) (PubMed:25136834). Expressed in plasma (at protein level) (PubMed:2448300). Expressed in serum (at protein level) (PubMed:29567995). The SMB domain mediates interaction with SERPINE1/PAI1. The heparin-binding domain mediates interaction with insulin. Sulfated on tyrosine residues. N- and O-glycosylated. Phosphorylation on Thr-69 and Thr-76 favors cell adhesion and spreading. It has been suggested that the active SMB domain may be permitted considerable disulfide bond heterogeneity or variability, thus two alternate disulfide patterns based on 3D structures are described with 1 disulfide bond conserved in both. Phosphorylation sites are present in the extracellular medium.