Apo α-lactalbumin and lysozyme are colocalized in their subsequently formed spherical supramolecular assembly

摘要

We have reported previously that the calcium-depleted form of bovine a-lactalbumin (apo a-LA) interacts with hen egg-white lysozyme (LYS) to form spherical supramolecular structures. These supramolecular structures contain an equimolar ratio of the two proteins. We further explore here the organization of these structures. The spherical morphology and size of the assembled LYS⁄ apo a-LA supramolecular structures were demonstrated using confocal scanning laser microscopy and scanning electron microscopy. From confocal scanning laser microscopy experiments with labelled proteins, it was found that LYS and apo a-LA were perfectly colocalized and homogeneously distributed throughout the entire three-dimensional structure of the microspheres formed. The spatial colocalization of the two proteins was also confirmed by the occurrence of a fluorescence resonance energy transfer phenomenon between labelled apo a-LA and labelled LYS. Polarized light microscopy analysis revealed that the microspheres formed differ from spherulites, a higher order semicrystalline structure. As the molecular mechanism initiating the formation of these microspheres is still unknown, we discuss the potential involvement of a LYS⁄ apo a-LA heterodimer as a starting block for such a supramolecular assembly.