Evolutionary insights reveal a new role of PADI2 in transcriptional elongation

Abstract Peptidyl arginine deiminases (PADIs) catalyze protein citrullination, a post-translational conversion of arginine to citrulline. The most widely expressed member of this family, PADI2, regulates cellular processes that impact several diseases. We hypothesized that we could gain new insights into PADI2 function through a systematic evolutionary and structural analysis. Here, we identify 20 positively selected PADI2 residues, 16 of which are structurally exposed and maintain PADI2 interactions with cognate proteins. Many of these selected residues reside in non-catalytic regions of PADI2. We validate the importance of a prominent loop in the middle domain that encompasses PADI2 L162, a residue under positive selection. This site is essential for interaction with the transcription elongation factor (P-TEFb) and mediates active transcription of the oncogenes c-MYC , and CCNB1, as well as impacting cellular proliferation. These insights could be key to understanding and addressing the role of the PADI2 c-MYC axis in cancer progression. Significance Statement Here we use a systematic evolutionary analysis to identify positively selected residues in the non-catalytic domain of PADI2 and link the positive selection of key residues to a role in transcription. Specifically, a structurally exposed loop in the PADI2 middle domain encompasses the positively selected residue L162 which is linked to transcription and cellular proliferation. This loop contributes to PADI2 interaction with the P-TEFb complex and cellular proliferation. Our results showcase the utility of combining evolutionary and experimental approaches to dissect the evolution of essential functional processes.