DCAF11 Supports Targeted Protein Degradation by Electrophilic Proteolysis-Targeting Chimeras

Ligand-induced protein degradation has emerged as a compelling approach to promote the targeted elimination of proteins from cells by directing these proteins to the ubiquitin-proteasome machinery. So far, only a limited number of E3 ligases have been found to support ligand-induced protein degradation, reflecting a dearth of E3-binding compounds for proteolysis-targeting chimera (PROTAC) design. Here, we describe a functional screening strategy performed with a focused library of candidate electrophilic PROTACs to discover bifunctional compounds that degrade proteins in human cells by covalently engaging E3 ligases. Mechanistic studies revealed that the electrophilic PROTACs act through modifying specific cysteines in DCAF11, a poorly characterized E3 ligase substrate adaptor. We further show that DCAF11-directed electrophilic PROTACs can degrade multiple endogenous proteins, including FBKP12 and the androgen receptor, in human prostate cancer cells. Our findings designate DCAF11 as an E3 ligase capable of supporting ligand-induced protein degradation via electrophilic PROTACs.

Chemical Protein Synthesis with the KAHA Ligation

Since the first report of the chemoselective amide bond forming reaction between α-ketoacids and hydroxylamines in 2006, the KAHA (α-ketoacid-hydroxylamine) ligation has advanced to a useful tool for the routine synthesis of small to medium sized proteins and cyclic peptides. In this chapter we introduce the concept of KAHA ligation starting with the synthesis and properties of hydroxylamines and α-ketoacids, methods for their incorporation into peptides, and give an insight into the mechanism of the KAHA ligation. We cover important improvements including sequential ligations with 5-oxaproline, traceless synthesis of peptide α-ketoacids and show their application in chemical protein synthesis and cyclic peptide synthesis. Recent developments of the KAT (potassium acyl trifluoroborate) ligation and its application as fast and chemoselective bioconjugation method are described and an outlook on ongoing work and possible future developments is given at the end of the chapter.