Proteins in the human body are usually made of 20 natural amino acids.Through different amino acid combinations and isomerization, proteins of diverse functions are built.An emerging genetic code expansion technology can introduce unnatural amino acids into specific sites of target protein, endowing the protein with new biological characteristics including covalently binding with proximal proteins, carrying fluorescence, and mimicking specific protein post-translational modifications.In this paper, based on the structure and function of unnatural amino acids, the applications of different types of unnatural amino acids in regulating protein''s stability, studying protein''s conformation, expression level, and localization, and uncovering heretofore unknown protein-protein interactions were reviewed.Besides, genetic code expansion of unnatural amino acids is anticipated to find broad utilities in biomedicine by bringing new ideas and methods to the design and optimization of biologics.

To investigate the effects of genistein (Gen) on the biosynthesis of N-glycolylneuraminic acid (Neu5Gc) in rats, 80 4-week-old male SD rats were randomly equally into the control and genistein groups. The rats of control and genistein groups were fed 5% ethanol and 300 mg/(kg·d) genistein respectively by gavage. The contents of Neu5Gc in hind leg muscle, kidney and liver tissues of rats were measured by using high performance liquid chromatography coupled with fluorescence detector (HPLC/FLD), and the mechanism of inhibition of Neu5Gc synthesis was investigated by using the molecular docking of Gen and sialyltransferase. On the 15th day, the content of Neu5Gc in hind leg muscle and liver tissues decreased 13.77% and 15.45%, respectively, and there was no significant change in the content of Neu5Gc in kidney tissues. On the 30th day, the content of Neu5Gc in liver tissues decreased 13.35%, however, there was no significant change in the content of Neu5Gc in kidney tissues and Neu5Gc was not detected in hind leg muscle. The content of Neu5Gc in hind leg muscle, kidney and liver tissues decreased respectively 32.65%, 32.78%, 16.80% and 12.72%, 11.42%, 12.30% while rats fed on the 45th and the 60th days. Genistein has formed the hydrogen bond with sialyltransferase activity site residues His319, Ser151, Gly293, Thr328 and formed a hydrophobic interactions with the residues His302, His301, Trp300, Ser271, Phe292, Thr328, Ser325 and Ile274. The results of molecular docking indicated that the weak intermolecular interaction was the main cause of genistein inhibiting sialyltransferase activity. The research results provided an experimental basis for the subsequent reduction of Neu5Gc in red meat before slaughter.
Animals ; Gene Expression Regulation, Enzymologic ; drug effects ; Genistein ; pharmacology ; Male ; Molecular Docking Simulation ; Neuraminic Acids ; metabolism ; Random Allocation ; Rats ; Rats, Sprague-Dawley ; Transferases ; metabolism