β-Amyloid Peptide 1-42-Conjugated Magnetic Nanoparticles for the Isolation and Purification of Glycoproteins in Egg White.

Aβ-conjugated magnetic nanoparticles, Aβ@MNP, were prepared by covalently coupling Aβ to hyperbranched polyethyleneimine (PEI)-modified magnetic nanoparticles via -(3-dimethylaminopropyl)-'-ethylcarbodiimide hydrochloride (EDC). Aβ's high binding capacity to glycosyl groups facilitates Aβ@MNP composite to be a promising selective adsorbent for glycoproteins in egg whites. In our study, under conditions of pH 4.0, the adsorption efficiency of Aβ@MNP composite for ovalbumin (100 μg mL) was 98.4% and its maximum adsorption capacity was 344.8 mg g ; under the condition of pH 4.0 and 200 mmol L NaCl, its adsorption efficiencies for ovalbumin and ovotransferrin were 96.9% and 60.0%, respectively. According to these primary data, in practice, ovalbumin was removed from egg white by Aβ@MNP composite at pH 4.0 (step I), and then after adding NaCl until the final salt concentration reached 200 mmol L (pretreated egg white), we utilized the same adsorbent to further isolate/purify glycoproteins (step II). SDS-PAGE results showed that Aβ@MNP composite could largely remove ovalbumin in step I and could isolate/purify the remaining ovalbumin and ovotransferrin in step II. LC-MS/MS analysis results showed that the removal of ovalbumin reduced its percentage in egg white samples from 32.93% to 11.05% in step I and the remaining ovalbumin and ovotransferrin were enriched in step II, where the final percentage reached 11.6% and 12.6%, respectively. In summary, 81 protein species were identified after two-step extraction with Aβ@MNP on egg white, while only 46 protein species were identified directly from raw egg white without any pretreatment. This work well illustrates the excellent adsorption performance of Aβ@MNP composite to glycoproteins and its potential in the application of proteomic studies on low-abundance proteins in egg white.