9.B.198 The Membrane-anchored Lipid-binding Protein (LAM) Family
Membrane contact sites are structures where two organelles come close together to regulate flow of material and information between them. One type of inter-organelle communication is lipid exchange, which must occur for membrane maintenance and in response to environmental and cellular stimuli. Soluble lipid transfer proteins have been extensively studied, but additional families of transfer proteins have been identified that are anchored into membranes by transmembrane helices. If such proteins target membrane contact sites, they may function in organellar lipid transfer. The eukaryotic family of so-called Lipid transfer proteins Anchored at Membrane contact sites (LAMs) all contain both a sterol-specific lipid transfer domain in the StARkin superfamily (related to StART/Bet_v1), and one or more transmembrane helices, anchoring them in the endoplasmic reticulum (ER). They target a variety of membrane contact sites, including contacts between organelles. Lam1-4p target punctate ER-plasma membrane contacts, while Lam5p and Lam6p target multiple contacts including vacuolar ER contacts. These developments confirm previous observations on tubular lipid-binding proteins (TULIPs) that establish the importance of membrane anchored proteins for lipid traffic (Wong and Levine 2016). However, it is not known if LAMs are transporters, or are regulators that affect traffic indirectly .