**Breakthrough Thianthrenium Reagent Transforms Protein Interaction Research**
An innovative advancement in chemical biology has been made at the Max-Planck Institute for Coal Research in Germany, under the leadership of Tobias Ritter. The research team has unveiled a new thianthrenium dication reagent (TTD), which facilitates the formation of short and stable protein crosslinks. This advancement is poised to improve the detection of less common protein–protein interactions (PPIs) within cellular environments.
PPIs are essential for comprehending cellular functions, as they significantly influence metabolism and various intracellular processes. Historically, investigating these interactions in their native settings has posed challenges, especially for transient and less stable interactions. Francis O’Reilly from St Jude Children’s Research Hospital points out that directly capturing interactions in the cell can uncover novel regulatory protein interactions that have often been missed.
In crosslinking mass spectrometry, chemical crosslinkers create covalent bonds between peptides, stabilizing the interactions for analysis. Many currently available crosslinkers, like homobifunctional *N*-hydroxysuccinimide ester crosslinkers, face limitations such as inadequate cellular permeability and false positive results, whereas others, including diazarines, are unable to incorporate tags.
The newly engineered TTD addresses these limitations by featuring an alkyne enrichment tag while ensuring short and stable links to cysteine through a rapid, one-step process. This is achievable through a highly reactive episulfonium intermediate. Its synthesis from commercially accessible reagents is efficient, and it maintains cell permeability due to an integrated ether, facilitating effective crosslinking within cellular contexts.
This advancement builds on prior research with vinylthianthrenium tetrafluoroborate (VTT), improving it by adding an affinity tag to better expose rarer PPIs. Ritter’s group confirmed their reagent’s efficacy by identifying both known and novel PPIs, underscoring its potential to unearth new drug targets.
Ritter highlights that while the discovery of new PPIs is encouraging, it serves as a proof of principle. The primary objective is to reveal many more interactions to convincingly showcase the reagent’s practical applications.
O’Reilly recognizes the significance of such pioneering chemistry in probing previously unreachable aspects of the proteome, noting that conventional methods such as NHS esters and diazirines have lacked a competent rival until this point. Despite some reservations regarding the biological interpretations derived from the new findings, the introduction of TTD signifies an exhilarating progress in chemical biology, with the promise of enhancing our comprehension of complex protein networks in cells.