Plasma membrane localization of StREM1.3 Remorin is mediated by conformational changes in a novel C-terminal anchor and required for the restriction of PVX movement.

The formation of plasma membrane (PM) micro-domains plays a crucial role in the regulation of membrane signalling and trafficking. Remorins are a plant-specific family of proteins organized in six phylogenetic groups, and Remorins of the group 1 are among the few plant proteins known to specifically associate with membrane rafts. As such, they are valuable to understand the molecular bases for PM lateral organization in plants. However, little is known about the structural determinants underlying group 1 Remorins specific association with membrane rafts. We used a structure-function approach to identify a short C-terminal anchor (RemCA) indispensable and sufficient for tight direct binding of Solanum tuberosum REMORIN 1.3 (StREM1.3) to the PM. RemCA switches from unordered to an alpha-helical structure in a non-polar environment. Protein structure modelling indicates that RemCA folds into a tight hairpin of amphipathic helices. Consistently, mutations reducing RemCA amphipathy abolished StREM1.3 PM localization. Furthermore, RemCA directly binds to biological membranes in vitro, shows higher affinity for Detergent-Insoluble Membranes (DIM) lipids, and targets YFP to DIMs in vivo. Mutations in RemCA resulting in cytoplasmic StREM1.3 localization abolish StREM1.3 function in restricting potato virus X movement. The mechanisms described here provide new insights on the control and function of lateral segregation of plant PM.