Small milk protein α-lactalbumin (α-LA), a component of lactose synthase, is a simple model Ca2+ binding protein, which does not belong to the EF-hand proteins, and a classical example of molten globule state. It has a strong Ca2+ binding site, which binds Mg2+, Mn2+, Na+, and K+, and several distinct Zn2+ binding sites. The binding of cations to the Ca2+ site increases protein stability against action of heat and various denaturing agents, while the binding of Zn2+ to the Ca2+-loaded protein decreases its stability. Functioning of α-LA requires its interactions with membranes, proteins, peptides and low molecular weight substrates and products. It was shown that these interactions are modulated by the binding of metal cations. Recently it was found that some folding variants of α-LA demonstrate bactericidal activity and some of them cause apoptosis of tumor cells.
