Effect of Denaturation of α-Lactalbumin on the Formation of BAMLET (Bovine α-Lactalbumin Made Lethal to Tumor Cells)

摘要

A complex of α-lactalbumin with oleic acid, also known as HAMLET/BAMLET (human/bovine α-lactalbumin made lethal to tumor cells), causes apoptosis-like death in tumor cells but has little effect on healthy differentiated cells. The aim of this study was to examine whether irreversible denaturation of α-lactalbumin is detrimental to the formation and cytotoxicity of BAMLET. Commercial bovine holo α-lactalbumin (1-4% w/v) was heated at 80 °C for up to 100 min. With an increasing concentration of protein, the denaturation of α-lactalbumin proceeded faster, and aggregation became more extensive. Native and sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that a high proportion of the aggregates was linked by disulfide bonds. BAMLET was prepared from native and heat-treated α-lactalbumin according to a previously described chromatographic method. Despite the high content of denatured and aggregated α-lactalbumin in the heat-treated samples, their conversion into BAMLET was not negatively affected, resulting in BAMLET complexes partly composed of covalently linked aggregates of α-lactalbumin. The cytotoxicity of all prepared BAMLET samples was comparable to that of the control sample prepared from native α-lactalbumin (LD_(50) = 34.6 ± 2.7 μmol L~(-1)). It was concluded that α-lactalbumin is not required to be in its native conformation for the conversion into its biologically active BAMLET complex.