Interaction Surface and Topology of Get3-Get4-Get5 Protein Complex, Involved in Targeting Tail-anchored Proteins to Endoplasmic Reticulum

Recent work has uncovered the “GET system,” which is responsible for endoplasmic reticulum targeting of tail-anchored proteins. Although structural information and the individual roles of most components of this system have been defined, the interactions and interplay between them remain to be elucidated. Here, we investigated the interactions between Get3 and the Get4-Get5 complex from Saccharomyces cerevisiae. We show that Get3 interacts with Get4-Get5 via an interface dominated by electrostatic forces. Using isothermal titration calorimetry and small-angle x-ray scattering, we further demonstrate that the Get3 homodimer interacts with two copies of the Get4-Get5 complex to form an extended conformation in solution. Background: The GET system mediates the insertion of tail-anchored (TA) proteins into the endoplasmic reticulum membrane. Results: The protein complex comprising most of the cytosolic portions of the GET system shows an extended conformation in solution. Conclusion: The ternary complex Get3-Get4-Get5 forms an elongated structure with 2:2:2 stoichiometry for conducting TA protein delivery. Significance: The structure provides a framework for TA protein insertion into the membrane.