BPS2026 – Investigating the dynamic response of the motor protein SecA during protein translocation

All organisms require protein transport across membranes, with the majority occurring through the ubiquitous Sec machinery. In bacteria, SecA, a cytosolic motor protein associates with SecY, the core protein channel, to enable efficient protein translocation, with the addition of ATP. SecA is known to undergo large conformational changes throughout the transport cycle and ATP hydrolysis; however, how these rearrangements are connected and drive directional protein transport across the membrane remains unclear. Here, a range of biophysical approaches are used to probe the different nucleotide states of SecA, how the conformational changes induced by ATP hydrolysis affect the dynamics of SecA’s domains, and how these changes influence the rest of the Sec system, specifically the SecY pore and lateral gate. This work is done in combination with molecular dynamics simulations exploiting equilibrium and non-equilibrium simulations, to explore the dynamic allosteric networks that span this complex and enable this rapid communication. Additionally, the Sec system is thought to respond to substrate, with “difficult” residue sequences (those containing stretches of heavily positive, or bulky amino acids for example), eliciting a response having been sensed by SecA, subsequently stimulating nucleotide hydrolysis to induce conformational changes that are then propagated throughout the system to drive directional transport. Here, a variety of substrates in both biophysical and simulated contexts, have been used to probe this sensing activity of SecA, and explore the response, to further understand the mechanism. Details of these findings will be presented during the poster session.