Chemoattractant. Activates the C-X-C chemokine receptor cxcr4 to induce a rapid and transient rise in the level of intracellular calcium ions, and chemotaxis. Signaling with cxcr4 mediates the directional movement of mesodermal cells during gastrulation. Binds to the allosteric site (site 2) of integrins and activates them in a cxcr4-independent manner. Monomer or homodimer; in equilibrium. Dimer formation is induced by non acidic pH and the presence of multivalent anions, and by binding to cxcr4 or heparin (By similarity). Belongs to the intercrine alpha (chemokine CxC) family.