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

Aβ1–42-conjugated magnetic nanoparticles, Aβ1–42@MNP, were prepared by covalently coupling Aβ1–42 to hyperbranched polyethyleneimine (PEI)-modified magnetic nanoparticles via N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC). Aβ1–42's high binding capacity to glycosyl groups facilitates Aβ1–42@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 Aβ1–42@MNP composite for ovalbumin (100 μg mL–1) was 98.4% and its maximum adsorption capacity was 344.8 mg g –1; under the condition of pH 4.0 and 200 mmol L–1 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 Aβ1–42@MNP composite at pH 4.0 (step I), and then after adding NaCl until the final salt concentration reached 200 mmol L–1 (pretreated egg white), we utilized the same adsorbent to further isolate/purify glycoproteins (step II). SDS-PAGE results showed that Aβ1–42@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 Aβ1–42@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 Aβ1–42@MNP composite to glycoproteins and its potential in the application of proteomic studies on low-abundance proteins in egg white.