Adhesive glycoprotein that mediates cell-to-cell and cell-to-matrix interactions. Binds heparin. May play a role in dentinogenesis and/or maintenance of dentin and dental pulp (By similarity). Ligand for CD36 mediating antiangiogenic properties. Plays a role in ER stress response, via its interaction with the activating transcription factor 6 alpha (ATF6) which produces adaptive ER stress response factors (By similarity). Homotrimer; disulfide-linked. Interacts (via the TSP type I repeats) with HRG; the interaction blocks the antiangiogenic effect of THBS1 with CD36 (By similarity). Can bind to fibrinogen, fibronectin, laminin, type V collagen and integrins alpha-V/beta-1, alpha-V/beta-3 and alpha-IIb/beta-3. Interacts (via the TSP type I repeats) with CD36; the interaction conveys an antiangiogenic effect. Interacts with ATF6 (via lumenal domain) (By similarity). Interacts with FN1; this interaction is enhanced by TNFAIP6, which may act as a bridging molecule between FN1 and THBS1. Secreted by thrombin-activated platelets and binds to the cell surface in the presence of extracellular Ca(2+) (PubMed:6777381). Incorporated into the extracellular matrix of fibroblasts (PubMed:6341993). Also detected in the endoplasmic reticulum and sarcoplasmic reticulum where it plays a role in the ER stress response (By similarity). Belongs to the thrombospondin family. Extended N-terminus.