Structurally derived universal mechanism for the catalytic cycle of the tail-anchored targeting factor Get3
Abstract
Tail-anchored (TA) membrane proteins, accounting for roughly 2% of proteomes, are primarily targeted posttranslationally to the endoplasmic reticulum membrane by the guided entry of TA proteins (GET) pathway. For this complicated process, it remains unknown how the central targeting factor Get3 uses nucleotide to facilitate large conformational changes to recognize then bind clients while also preventing exposure of hydrophobic surfaces.
Here, we identify the GET pathway in Giardia intestinalis and present the structure of the Get3-client complex in the critical postnucleotide-hydrolysis state, demonstrating that Get3 reorganizes the client-binding domain (CBD) to accommodate and shield the client transmembrane helix. Four additional structures of GiGet3, spanning the nucleotide-free (apo) open to closed transition and the ATP-bound state, reveal the details of nucleotide stabilization and occluded CBD.
This work resolves key conundrums and allows for a complete model of the dramatic conformational landscape of Get3. Clemons and colleagues identify a guided entry of tail-anchored proteins (GET) pathway in the pathogen Giardia intestinalis and characterize it structurally, revealing several previously unknown structures of the central protein Get3.
The work resolves some important open questions and results in a comprehensive model for the insertion of tail-anchored membrane proteins.