TGD4 of 479 aas and 19 - 21 putative beta strands in a β-barrel structure (Wang et al. 2013) that may form a porin to transfer lipids from the ER across the outer chloroplast membrane. TGD5 (TC#8.A.86; 91 aas and 2 TMSs) may function to transfer lipids from the ER to TGD4, and then to the TGD123 ABC complex (TC# 3.A.1.27.1.2) in the inner envelope membrane for import into the chloroplast inner membrane or matrix (Fan et al. 2015).