Purification of the lipid transfer protein tricalbin 3 in a native environment by using an amphiphilic copolymer

Membrane contact sites play crucial roles in regulating cellular membrane homeostasis and ion homeostasis. However, due to limitations in technical methods, it has been challenging to effectively identify the lipid components enriched around specific membrane proteins. Therefore, it remains difficult to clarify which lipid molecules serve as substrates for lipid transfer proteins and scramblases functioning at membrane contact sites and which lipids regulate their activities. Here, we describe a system using the amphipathic polymer poly(acrylic acid-co-styrene) to purify lipid transfer protein tricalbin 3 (Tcb3), which is anchored to the endoplasmic reticulum and mediates contacts with the plasma membrane. Through this process, Tcb3 can be solubilized in aqueous solution without the need for detergent treatment, which removes the lipid molecules surrounding the proteins. This process enables purification of the lipid molecules in the native membrane environment along with Tcb3.