A nexus of intrinsic dynamics underlies translocase priming

Abstract

Summary The cytoplasmic ATPase SecA and the membrane-embedded SecYEG channel assemble to form the functional Sec translocase. How this interaction primes and catalytically activates the translocase remains unclear. We now show that priming exploits a sophisticated nexus of intrinsic dynamics in SecA. Using atomistic simulations, single molecule FRET and hydrogen/deuterium exchange mass spectrometry we reveal multiple distributed dynamic islands that cross-talk with domain and quaternary motions. These dynamic elements are highly conserved and essential for function. Central to the nexus is a slender Stem through which, motions in the helicase ATPase domain of SecA biases how the preprotein binding domain rotates between open-closed clamping states. Multi-tier dynamics are enabled by an H-bonded framework covering most of the SecA structure and allowing conformational alterations with minimal energy inputs. As a result, dimerization, the channel and nucleotides select pre-existing conformations, and alter local dynamics to restrict or promote catalytic activity and clamp motions. These events prime the translocase for high affinity reception of non-folded preprotein clients. Such dynamics nexuses are likely universal and essential in multi-liganded protein machines.