Reflecting recent work in the

Chemical protein synthesis, through the chemoselective ligation of peptide segments, has provided an integral tool to study how post-translational modifications influence protein structure and function.

In this collaborative study between the University of Sydney and Novo Nordisk A/S, the authors have leveraged recently developed Diselenide-Selenoester Ligation (DSL) chemistry with Native Chemical Ligation (NCL) to prepare phosphorylated IGFBP-2. Comprising 290 residues and 9 disulfide bonds, this represents one of the most complex protein targets ever synthesized.

The target was disconnected into 8 smaller peptide fragments which could be assembled in a convergent manner through orthogonal deprotection and activation methods. Following folding and purification, synthetic IGFBP-2 was characterized by circular dichroism and mass spectrometry before verification of IGF binding affinity, all of which were found to be comparable to recombinantly produced IGFBP-2.