HDX-MS of the TRAMP Complex with tRNA

TRAMP is a eukaryotic protein complex with RNA helicase and polyadenylase activity that marks and delivers a variety of RNA substrates to the nuclear exosome for degradation. Prior work has characterized binding of Trf4 and Air2 to the helicase core of Mtr4 and the regulation of both enzymatic activities in TRAMP. Air2 contains a conserved sequence that is predicted to bind the arch domain of Mtr4, though this interface is dispensable for TRAMP formation. To understand the interactions of the Saccharomyces cerevisiae TRAMP complex and its interactions with RNA, we have applied hydrogen-deuterium exchange mass spectrometry. We demonstrate that Air2 simultaneously binds the helicase core and the fist of Mtr4 in solution, constraining the arch to a conformation ready to bind RNA. We characterize the previously unknown interactions of Trf4 and Air2 with RNA and show how interactions with substrates are altered in TRAMP, supporting a mechanistic model for the enhancement of Mtr4 activity in TRAMP.