RT Journal Article SR Electronic T1 Structural predictions of the SNX-RGS proteins suggest they belong to a new class of lipid transfer proteins JF bioRxiv FD Cold Spring Harbor Laboratory SP 2021.11.30.470681 DO 10.1101/2021.11.30.470681 A1 Blessy Paul A1 Saroja Weeratunga A1 Vikas A. Tillu A1 Hanaa Hariri A1 W. Mike Henne A1 Brett M. Collins YR 2022 UL http://biorxiv.org/content/early/2022/01/11/2021.11.30.470681.abstract AB Recent advances in protein structure prediction using machine learning such as AlphaFold2 and RosettaFold presage a revolution in structural biology. Genome-wide predictions of protein structures are providing unprecedented insights into their architecture and intradomain interactions, and applications have already progressed towards assessing protein complex formation. Here we present detailed analyses of the sorting nexin proteins that contain regulator of G-protein signalling domains (SNX-RGS proteins), providing a key example of the ability of AlphaFold2 to reveal novel structures with previously unsuspected biological functions. These large proteins are conserved in most eukaryotes and are known to associate with lipid droplets (LDs) and sites of LD-membrane contacts, with key roles in regulating lipid metabolism. They possess five domains, including an N-terminal transmembrane domain that anchors them to the endoplasmic reticulum, an RGS domain, a lipid interacting phox homology (PX) domain and two additional domains named the PXA and PXC domains of unknown structure and function. Here we report the crystal structure of the RGS domain of sorting nexin 25 (SNX25) and show that the AlphaFold2 prediction closely matches the experimental structure. Analysing the full-length SNX-RGS proteins across multiple homologues and species we find that the distant PXA and PXC domains in fact fold into a single unique structure that notably features a large and conserved hydrophobic pocket. The nature of this pocket strongly suggests a role in lipid or fatty acid binding, and we propose that these molecules represent a new class of conserved lipid transfer proteins.Competing Interest StatementThe authors have declared no competing interest.