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1.B.82 The Chloroplast Trigalactosyldiacylglycerol-4 Porin (TGD4) Family. 

Chloroplast membrane lipid synthesis relies on the import of glycerolipids from the ER. The TGD (TriGalactosylDiacylglycerol) proteins are required for this lipid transfer process. The TGD1, 2, and 3 proteins form an ABC (ATP-binding cassette) transporter transporting ER-derived lipids through the inner envelope membrane of the chloroplast, while TGD4 binds phosphatidic acid (PtdOH) and resides in the outer chloroplast envelope. Wang et al. 2013 identified two sequences in TGD4, amino acids 1-80 and 110-145, which are necessary and sufficient for PtdOH binding. Deletion of both sequences abolished PtdOH binding activity. They also found that TGD4 from 18:3 plants bound specifically and with increased affinity PtdOH. TGD4 did not interact with other proteins and formed a homodimer both in vitro and in vivo. Their results suggested that TGD4 is an integral dimeric β-barrel lipid transfer protein that binds PtdOH with its N terminus and contains dimerization domains at its C terminus (Wang et al. 2013).

References associated with 1.B.82 family:

Fan, J., Z. Zhai, C. Yan, and C. Xu. (2015). Arabidopsis TRIGALACTOSYLDIACYLGLYCEROL5 Interacts with TGD1, TGD2, and TGD4 to Facilitate Lipid Transfer from the Endoplasmic Reticulum to Plastids. Plant Cell 27: 2941-2955. 26410300
Wang, Z., N.S. Anderson, and C. Benning. (2013). The phosphatidic acid binding site of the Arabidopsis trigalactosyldiacylglycerol 4 (TGD4) protein required for lipid import into chloroplasts. J. Biol. Chem. 288: 4763-4771. 23297418