| Summary: | α-Lactalbumin (α-LA) is a small (Mr 14,200), acidic (pI 4–5), Ca<sup>2+</sup>-binding protein. α-LA is a regulatory component of lactose synthase enzyme system functioning in the lactating mammary gland. The protein possesses a single strong Ca<sup>2+</sup>-binding site, which can also bind Mg<sup>2+</sup>, Mn<sup>2+</sup>, Na<sup>+</sup>, K<sup>+</sup>, and some other metal cations. It contains several distinct Zn<sup>2+</sup>-binding sites. Physical properties of α-LA strongly depend on the occupation of its metal binding sites by metal ions. In the absence of bound metal ions, α-LA is in the molten globule-like state. The binding of metal ions, and especially of Ca<sup>2+</sup>, increases stability of α-LA against the action of heat, various denaturing agents and proteases, while the binding of Zn<sup>2+</sup> to the Ca<sup>2+</sup>-loaded protein decreases its stability and causes its aggregation. At pH 2, the protein is in the classical molten globule state. α-LA can associate with membranes at neutral or slightly acidic pH at physiological temperatures. Depending on external conditions, α-LA can form amyloid fibrils, amorphous aggregates, nanoparticles, and nanotubes. Some of these aggregated states of α-LA can be used in practical applications such as drug delivery to tissues and organs. α-LA and some of its fragments possess bactericidal and antiviral activities. Complexes of partially unfolded α-LA with oleic acid are cytotoxic to various tumor and bacterial cells. α-LA in the cytotoxic complexes plays a role of a delivery carrier of cytotoxic fatty acid molecules into tumor and bacterial cells across the cell membrane. Perhaps in the future the complexes of α-LA with oleic acid will be used for development of new anti-cancer drugs.
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