Figure 1. Multiple protein insertases have lipid scrambling activity in vitro.

(a) Schematic of the BSA back extraction assay. (b-e) Members of the Oxa1 superfamily (YidC, Oxa1, Get1, and the Get1/2 complex) can scramble glycerophospholipids. (f-g) The β-barrel membrane protein insertase, Sam50 in complex with Sam35 and Sam37, and the bacterial ortholog of Sam50, BamA, have scrambling activity. (h) The outer mitochondrial membrane insertase MTCH2 scrambles. (i-j) Negative controls, GlpG and VAMP2, do not scramble. Proteoliposomes used in the assays were analyzed by SDS-PAGE (insets) to confirm efficient reconstitution; approximate numbers for proteins/liposome were estimated assuming 50% recovery of lipids after reconstitution. (See Methods for exact liposome compositions, details of which varied according to experimentalist.)