Cryo-EM structural observation on the interaction of the bacterial energy-coupling factor transporter with perfluoroalkyl substances

The movement of exogenous chemicals through cell membranes using transport proteins and causing functional impairments to organisms is an important issue of molecular ecology. Per- and polyfluoroalkyl substances (PFAS) receives intensive concern by their global contamination and a limited understanding of their biological effects. Energy-coupling factor (ECF) transporters are critical to the absorption of vital micronutrients by bacteria and archaea, playing a significant role in maintaining microecological health. Our study found perfluorooctane sulfonate (PFOS) as an inhibitor on folate ECF transporter through competitive binding with folate and conformational alterations in ATP-binding domains, resulting in reduced folate absorption and ATPase activity. Molecular dynamics simulations depicted the process of PFOS internalization into plasma membrane prior to contact with ECF transporter. Using cryogenic electron microscopy (cryo-EM), we observed the conformational alterations caused by PFOS. The interaction mechanism between PFOS and folate ECF transporter was finally revealed though the combined approaches of cryo-EM and molecular simulation and elucidated as three critical pathway: membrane perturbation, competitive binding, and conformational changes. These findings reveal the functional impairments of exogenous chemicals on ECF transporters and advance the knowledge of ecotoxicity of PFAS.