Lanthanum silicate coated magnetic microspheres as a promising affinity material for phosphopeptide enrichment and identification

Novel Fe3O4@La (x) Si (y) O-5 affinity microspheres consisting of a superparamagnetic Fe3O4 core and an amorphous lanthanum silicate shell have been synthesized. The core-shell-structured Fe3O4@La (x) Si (y) O-5 microspheres, with a mean size of ca. 480 nm, had rough lanthanum silicate surfaces and displayed relatively strong magnetism (47.2 emu g(-1)). This novel affinity material can be used for selective capture, rapid magnetic separation, and part dephosphorylation (which plays an important role in identifying phosphopeptides in MS) of the phosphopeptides in a peptide mixture. Its ability to selectively trap and magnetically isolate as well as label the phosphopeptides was evaluated using a standard phosphorylated protein (beta-casein) and a real sample (human serum). Phosphopeptides and their corresponding label ions were detected for concentrations of beta-casein as low as 1 x 10(-9) M and in mixtures of beta-casein and BSA with molar ratios as low as 1:50. In addition, this affinity material, with its labeling properties, is superior to commercial TiO2 beads in terms of interference from non-phosphopeptide molecules. These results reveal that the lanthanum silicate coated magnetic microspheres represent a promising affinity material for the rapid purification and recognition of phosphopeptides.