The client-binding domain of the cochaperone Sgt2 has a helical-hand structure that binds a short hydrophobic helix
The targeting and insertion of tail-anchored (TA) integral membrane proteins (IMP) into the correct membrane is critical for cellular homeostasis. The fungal protein Sgt2, and its human homolog SGTA, binds hydrophobic clients and is the entry point for targeting of ER-bound TA IMPs. Here we reveal molecular details that underlie the mechanism of Sgt2 binding to TA IMP clients. We establish that the Sgt2 C-terminal region is flexible but conserved and sufficient for client binding. A molecular model for this domain reveals a helical hand forming a hydrophobic groove, consistent with a higher affinity for TA IMP clients with hydrophobic faces and a minimal length of 11 residues. This work places Sgt2 into a broader family of TPR-containing co-chaperone proteins.
The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY 4.0 International license. bioRxiv preprint first posted online Jan. 10, 2019. Version 2 posted September 16, 2020. We thank D. G. VanderVelde for assistance with NMR data collection; S. Mayo for providing computing resources; S. Shan, H. J. Cho, Y. Liu, and members of the Clemons lab for support and discussion. We thank J. Mock and A. M. Thinn for comments on the manuscript. This work was supported by the National Institutes of Health (NIH) grants GM105385 and GM097572 (to WMC), NIH/National Research Service Award Training Grant GM07616 (to SMS and MYF), and a National Science Foundation Graduate Research fellowship Grant 1144469 (to SMS). Data and Code Availability: All configuration, analysis, and figure generation code employed is available openly at github.com/clemlab/sgt2a-modeling with analysis done in Jupyter Lab/Notebooks using Python 3.6 enabled by Numpy, Pandas, Scikit-Learn, BioPython, and Bokeh [106-111]. The system topology and output files (including trajectory sampled at 0.5 ns intervals) can be permanently found here: 10.22002/D1.1100.
Submitted - 517573v2.full.pdf