Vitamin D-binding protein (Gc-globulin) binds actin.

Actin, an ubiquitous highly conserved intracellular protein, and the serum vitamin D-binding protein (DBP) form tight 1:1 molar complexes in vitro. This interaction, which is not species-specific, explains the widespread occurrence of the 5-6 S protein responsible for the binding of 25-hydroxycholecalciferol in high speed supernatants of all nucleated tissues. Incubation of F-actin, the filamentous form of this protein, with DBP leads to depolymerization of the former. Actin, complexed with deoxyribonuclease I, retains its ability to bind DBP. Erythrocyte actin, prepared from red cell ghosts, also displays binding properties for DBP. The biological significance of this new interaction of actin is not yet understood.