Profiling of reactive Cysteines
  • Developments in the fields of molecular glues, PROTACs and other new chemical modalities open exciting strategies to target proteins so far conceived as "undruggable"
  • In particular, reactive cysteines are attractive targets for the discovery of new covalent drugs
  • CysScout™ is a quantitative mass-spectrometry based chemoproteomics platform that enables the comprehensive mapping of reactive cysteines in a given system. Experiments in cells or lysates typically result in the identification of more than 20,000 distinct reactive cysteine sites for over 8,000 proteins
  • We already indexed over 46,000 reactive cysteine sites for more than 9,000 proteins and counting. Proprietary data are available for many standard cell lines (reach out for more details).
  • CysScout™ experiments with cysteine reactive compounds allow to uncover their molecular (off-)targets, to derive specificity and selectivity data, and to show target engagement
  • Due to its high through-put capabilities this technology is well suited to screen large substance or fragment libraries


Further reading

Kuljanin, M. et al. Reimagining high-throughput profiling of reactive cysteines for cell-based screening of large electrophile libraries. Nat Biotechnol 39, 630–641 (2021) [Link]

Weerapana, E. et al. Quantitative reactivity profiling predicts functional cysteines in proteomes. Nature 468, 790–795 (2010) [Link]

CysScout™ Example Study: Analysis of the kRASG12C Inhibitor ARS-1620
CysScout™ was employed to investigate the effect of ARS-1620 at different concentrations on a lung cancer cell line after 4 h to test compound selectivity and efficacy ARS-1620 is known to covalently bind to kRAS G12C mutant In this experiment, we analysed >8,000 reactive cysteines Only for kRAS G12C and Heme Oxigenase 2 C282 we detected a significant concentration-dependent intensity reduction of tagged cysteine peptides
CysScout™ Workflow
CysScout™ Workflow
The CysScout™ probe binds to the reactive cysteine sites under close to physiological conditions. The probe stays covalently attached during the following digest and labelling steps. After the labelling the samples are merged into one. Only peptides with a covalently bound probe will be retained in the enrichment step and analysed by LC-MS. The label allows to quantify the relative amount of each cysteine reactive site within the multiplexed sample. Sites targeted by a tested compound will show low signal compared to the indexing experiment.