What is one of the amino acids used in the biosynthesis of proteins, that is in a synthetic peptide consisting of eight amino acids?
Strep-tag:  The Strep-tag II is a synthetic peptide consisting of eight amino acids (Trp-Ser-His-Pro-Gln-Phe-Glu-Lys). Histidine: Histidine (abbreviated as His or H; encoded by the codons CAU and CAC) is an α-amino acid that is used in the biosynthesis of proteins.
Histidine