Intricate coupling between the transactivation and basic-leucine zipper domains governs phosphorylation of transcription factor ATF4 by casein kinase 2.

Abstract

Transcription factors (TFs) play the first and fundamental role in cellular gene expression. TFs possess two main functional domains, transactivation domain (TAD) and DNA binding domain (DBD). Most transactivation domains are known to be largely disordered but play a key role in modulating the transcriptional activity by binding to a variety of coactivators and corepressors. Despite the crucial importance of these domains, the structural and functional basis of transactivation remains poorly understood and that's one of the main reasons why TFs are considered “undruggable”. Here, we focused on activating transcription factor 4 (ATF4), an essential transcription factor for cellular stress adaptation. Using solution nuclear magnetic resonance spectroscopy complemented by a range of biophysical methods, we found that the isolated transactivation domain of ATF4 is predominantly yet not fully disordered in solution. Importantly, we found that the N-terminal region of TAD is involved in transient long-range interactions with its DBD, also known as basic-leucine zipper (bZip) domain. Finally, in vitro phosphorylation assays with the CKII kinase show that the presence of the bZip domain is required for phosphorylation of TAD. This study uncovers the intricate coupling existing between the TAD and DNA binding domains of ATF4, highlighting its potential regulatory significance.