?-Lactalbumin, Amazing Calcium-Binding Protein.
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ABSTRACT: ?-Lactalbumin (?-LA) is a small (Mr 14,200), acidic (pI 4-5), Ca2+-binding protein. ?-LA is a regulatory component of lactose synthase enzyme system functioning in the lactating mammary gland. The protein possesses a single strong Ca2+-binding site, which can also bind Mg2+, Mn2+, Na+, K+, and some other metal cations. It contains several distinct Zn2+-binding sites. Physical properties of ?-LA strongly depend on the occupation of its metal binding sites by metal ions. In the absence of bound metal ions, ?-LA is in the molten globule-like state. The binding of metal ions, and especially of Ca2+, increases stability of ?-LA against the action of heat, various denaturing agents and proteases, while the binding of Zn2+ to the Ca2+-loaded protein decreases its stability and causes its aggregation. At pH 2, the protein is in the classical molten globule state. ?-LA can associate with membranes at neutral or slightly acidic pH at physiological temperatures. Depending on external conditions, ?-LA can form amyloid fibrils, amorphous aggregates, nanoparticles, and nanotubes. Some of these aggregated states of ?-LA can be used in practical applications such as drug delivery to tissues and organs. ?-LA and some of its fragments possess bactericidal and antiviral activities. Complexes of partially unfolded ?-LA with oleic acid are cytotoxic to various tumor and bacterial cells. ?-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 ?-LA with oleic acid will be used for development of new anti-cancer drugs.
SUBMITTER: Permyakov EA
PROVIDER: S-EPMC7565966 | biostudies-literature | 2020 Aug
REPOSITORIES: biostudies-literature
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