Experimental and in silico approaches to study the interaction of Remorin with plant plasma membrane : specific interaction of the C-term domain with lipids

The function of Remorins, a diverse family of plant-specific proteins (1) is far to be fully elucidated. One of them, StREM1.3 (for Solanum tuberosum Remorin from group 1, homolog 3) has been reported to regulate cell-to-cell propagation of the potato virus X (2). It was also shown to be localized to the inner leaflet of plasma membranes (PMs) and along plasmodesmata, bridges connecting neighbor cells essential for cell-to-cell communication in plants (3). The mechanisms driving StREM1.3 association with PM is still an open question. It was shown recently that a domain of 28 residues at the C-terminus of the potato (RemCA) is required and sufficient for anchoring to the PM (4).
Here we combined experimental and in silico biophysics to unravel the molecular bases of RemCA membrane binding. Biomimetic membrane models of plant PM such as monolayers and liposomes were used with various biophysical techniques (Langmuir monolayer technique, Fourier-transformed infrared spectroscopy, circular dichroïsm) and modeling tools (home-made methods and molecular dynamics) (5) to answer to three questions: (i) What is the conformation adopted by RemCA within a membrane?, (ii) Is there any membrane lipid specificity in the RemCA-membrane binding? (iii) What is the role of the two different RemCA domains in the interaction?
Results show that RemCA displays a preference for plant phosphoinositide and sitosterol-enriched inner leaflet plasma membrane rafts. Within the membrane, the C-terminal and the N-terminal domains adopt a random coil and a -helical conformation respectively. The C-terminal domain acts as a driver to bind RemCA to the membrane while the N-terminal domain stabilizes the peptide at the membrane. Lysine residues have a crucial importance in this interaction.

References
(1) Raffaele et al., Plant Physiol., 2007, 145: 593–600
(2) Raffaela et al., Plant Cell, 2009, 21: 1541–1555.
(3) Maule, Curr. Opin. Plant Biol., 2008, 11: 680–686.
(4) Perraki et al., Plant Physiology, 2012, 160 : 624-637.
(5) Deleu et al., Biochim. Biophys. Acta – Biomembranes, 2014, 1838 : 3171-3190.