The power of chemoselectivity: functional protein-conjugates for intra- and extracellular targeting

Our lab aims to identify new bioorthogonal reactions for the synthesis and modification of functional peptides and proteins. We apply these highly selective organic reactions¹ to study functional consequences of naturally occurring posttranslational protein modifications (PTMs), in particular phosphorylated Lys- and Cystein-peptides,² as well as to generate novel peptide- and protein-conjugates for pharmaceutical and medicinal applications. In this presentation l will focus on the chemical modification of functional proteins as well as their cellular delivery. Thereby, we employ cyclic cell penetrating peptides (cCPPs) to transport a functional full length protein to specific intracellular compartments of living cells as recently demonstrated by the direct delivery of different fluorescent proteins.³ For protein modification we use a combined approach of intein expression as well as recently developed chemoselective reactionsand enzymatic ligations, for instance the so-called P5⁴ or Tub-tag labeling.⁵  This concept is finally applied to generate new antibody-drug conjugates^4b as well as cell-permeable nanobodies, i.e. small antigen binding proteins that remain active within the reductive milieu inside living cells, to interfere with intracellular targets.⁶