ER membrane receptors of the GET pathway are conserved throughout eukaryotes

LISA YASMIN ASSECK; DIETMAR GERALD MEHLHORN; JHON RIVERA MONROY; MARTINIANO MARIA RICARDI; HOLGER BREUNINGER; NIKLAS WALLMEROTH; KENNETH WAYNE BERENDZEN; MINOU NOWROUSIAN; SHUPING XING; BLANCHE SCHWAPPACH; MARTIN BAYER; CHRISTOPHER GREFEN

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA

NATL ACAD SCIENCES

Año: 2021 vol. 118

0027-8424

Type II tail-anchored (TA) membrane proteins are involved in diverse cellular processes such as protein translocation, vesicle trafficking and apoptosis. They are characterized by a single C-terminal transmembrane domain that mediates post-translational targeting and insertion into the endoplasmic reticulum (ER) via the Guided-Entry of Tail-anchored Proteins (GET) pathway. The GET system was originally described in mammals and yeast but was recently shown to be partially conserved in other eukaryotes such as higher plants. A newly synthesized TA protein is shielded from the cytosol by a pre-targeting complex and an ATPase which delivers the protein to the ER where membrane receptors (Get1/WRB & Get2/CAML) facilitate insertion. In the model plant Arabidopsis thaliana, most components of the pathway were identified through in silicosequence comparison, however, a functional homolog of the co-receptor Get2/CAML remained elusive. We performed immunoprecipitation-mass spectrometry analysis to detect in vivointeractors of AtGET1 and identified a membrane protein of unknown function with low sequence but high structural homology to both, yeast Get2, and mammalian CAML. The protein localises to the ER membrane, coexpresses with AtGET1 and binds to ArabidopsisGET pathwaycomponents. While loss-of-functionlines phenocopy the stunted root-hair phenotype of other Atgetlines, its heterologous expression together with the co-receptor AtGET1 rescues growth defects of Δget1get2yeast. Ectopic expression of the cytosolic, positively charged N-terminus is sufficient to block TA protein insertion in vitro. Our results collectively confirm that we have identified a plant-specific GET2 in Arabidopsisand its sequence allows the analysis of cross-kingdom pathway conservation.