title: Realizing serine/threonine ligation: scope and limitations and mechanistic implication thereof.
abstract: Serine/Threonine ligation (STL) has emerged as an alternative tool for protein chemical synthesis, bioconjugations as well as macrocyclization of peptides of various sizes. Owning to the high abundance of Ser/Thr residues in natural peptides and proteins, STL is expected to find a wide range of applications in chemical biology research. Herein, we have fully investigated the compatibility of the STL strategy for X-Ser/Thr ligation sites, where X is any of the 20 naturally occurring amino acids. Our studies have shown that 17 amino acids are suitable for ligation, while Asp, Glu, and Lys are not compatible. Among the working 17 C-terminal amino acids, the retarded reaction resulted from the bulky β-branched amino acid (Thr, Val, and Ile) is not seen under the current ligation condition. We have also investigated the chemoselectivity involving the amino group of the internal lysine which may compete with the N-terminal Ser/Thr for reaction with the C-terminal salicylaldehyde (SAL) ester aldehyde group. The result suggested that the free internal amino group does not adversely slow down the ligation rate.
authors.affiliation: Department of Chemistry, The University of Hong Kong Hong Kong, China ; State Key Laboratory of Synthetic Chemistry, University of Hong Kong Hong Kong, China.
authors.forename: Clarence T T
authors.initials: CT
authors.lastname: Wong
authors.affiliation: Department of Chemistry, The University of Hong Kong Hong Kong, China ; State Key Laboratory of Synthetic Chemistry, University of Hong Kong Hong Kong, China.
authors.forename: Tianlu
authors.initials: T
authors.lastname: Li
authors.affiliation: Department of Chemistry, The University of Hong Kong Hong Kong, China ; State Key Laboratory of Synthetic Chemistry, University of Hong Kong Hong Kong, China.
authors.forename: Hiu Yung
authors.initials: HY
authors.lastname: Lam
authors.affiliation: Department of Chemistry, The University of Hong Kong Hong Kong, China ; State Key Laboratory of Synthetic Chemistry, University of Hong Kong Hong Kong, China.
authors.forename: Yinfeng
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, The University of Hong Kong Hong Kong, China ; State Key Laboratory of Synthetic Chemistry, University of Hong Kong Hong Kong, China ; Shenzhen Institute of Research and Innovation of The University of Hong Kong Shenzhen, China.
authors.forename: Xuechen
authors.initials: X
authors.lastname: Li
keywords: chemoselectivity; peptide ligation; peptide synthesis; protein synthesis; solid phase peptide synthesis