title: Site Selective Azo Coupling for Peptide Cyclization and Affinity Labeling of an SH3 Protein.
abstract: A key challenge in bioconjugation is to control the site selectivity of the reaction. Chemical reagents often react with proteineous chemical groups without showing preference to their location or microenvironment in the protein; to confine the reaction to an amino acid at a specific site, one needs to distinguish this residue from others despite their identical chemical properties. Here, we report a strategy that utilizes proximity-driven reactivity to achieve site selective azo coupling between tyrosine and aryldiazonium. A phenylalanine analogue with an aryldiazonium moiety at its side chain was incorporated into a synthetic peptide and was found to react only with tyrosine in its vicinity but also to remain inert to others that are not immediately adjacent, a property attained by fine regulation of the electronic effect of the substituent on the aryl ring. Proximity-driven intramolecular azo coupling was showcased in cyclization of a β-hairpin peptide, structural features of the azo linked cyclic peptide was elucidated by NMR, and intermolecular azo coupling was achieved between an SH3 protein Abl-SH3 and its polyproline peptide ligands at specific tyrosine residues. This approach is generally applicable to develop covalent affinity labels for SH3 proteins because of the high occurrence rate of tyrosine at the peptide-binding site of SH3 proteins.
authors.affiliation: †Department of Chemistry, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Huang
authors.affiliation: †Department of Chemistry, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China.
authors.forename: Yunyu
authors.initials: Y
authors.lastname: Nie
authors.affiliation: ‡Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong SAR, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Ye
authors.affiliation: ‡Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong SAR, China.
authors.forename: Mingjie
authors.initials: M
authors.lastname: Zhang
authors.affiliation: †Department of Chemistry, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China.
authors.forename: Jiang
authors.initials: J
authors.lastname: Xia
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D001391:Azo Compounds / Q000737:chemistry*; D001665:Binding Sites; D003500:Cyclization; D006801:Humans; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010456:Peptides, Cyclic / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D016315:Proto-Oncogene Proteins c-abl / Q000737:chemistry*; D018909:src Homology Domains
chemical_list: D000596:Amino Acids; D001391:Azo Compounds; D008024:Ligands; D010456:Peptides, Cyclic; D016315:Proto-Oncogene Proteins c-abl