Enables signaling receptor binding activity. Involved in several processes, including positive regulation of cell population proliferation; positive regulation of macromolecule metabolic process; and positive regulation of signal transduction. Acts upstream of or within cell activation. Located in extracellular space. Part of alphav-beta3 integrin-IGF-1-IGF1R complex and insulin-like growth factor ternary complex. Implicated in several diseases, including acne; brain ischemia; diabetes mellitus (multiple); myopia; and neurodegenerative disease (multiple). Biomarker of several diseases, including Henoch-Schoenlein purpura; artery disease (multiple); autoimmune disease (multiple); bone disease (multiple); and eye disease (multiple).