8.A.86 The Chloroplast Trigalactosyldiacylglycerol-5 (TGD5) Protein Family. 

TGD5 facilitates lipid transfer from the outer to the inner plastid envelope by bridging TGD4 (TC# 1.B.82.1.1) with the TGD1,2,3 transport complex (3.A. TGD5 is required for endoplasmic reticulum-to-plastid lipid trafficking as part of the eukaryotic pathway of thylakoid lipid assembly (Fan et al. 2015).  Disruption of TGD5 results in phenotypic effects similar  to those for tgd1,2,3,4 mutants, including deficiency of ER-derived thylakoid lipids, accumulation of oligogalactolipids, and triacylglycerol. Genetic analysis indicated that TGD4 is epistatic to TGD5 in ER-to-plastid lipid trafficking, whereas double mutants of a null tgd5 allele with tgd1-1 or tgd2-1 showed a synergistic embryo-lethal phenotype. TGD5 is a small glycine-rich protein that is localized in the envelope membranes of chloroplasts. Coimmunoprecipitation assays suggested that TGD5 physically interacts with TGD1, TGD2, TGD3, and TGD4. Collectively, these results suggest that TGD5 facilitates lipid transfer from the outer to the inner plastid envelope by bridging TGD4 with the TGD1,2,3 transporter complex (Fan et al. 2015).



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.

Paolillo, R., I. Spinello, M.T. Quaranta, L. Pasquini, E. Pelosi, F. Lo Coco, U. Testa, and C. Labbaye. (2015). Human TM9SF4 Is a New Gene Down-Regulated by Hypoxia and Involved in Cell Adhesion of Leukemic Cells. PLoS One 10: e0126968.

Perrin, J., M. Mortier, A.C. Jacomin, P. Viargues, D. Thevenon, and M.O. Fauvarque. (2015). The nonaspanins TM9SF2 and TM9SF4 regulate the plasma membrane localization and signalling activity of the peptidoglycan recognition protein PGRP-LC in Drosophila. J Innate Immun 7: 37-46.

Pruvot, B., V. Laurens, F. Salvadori, E. Solary, L. Pichon, and J. Chluba. (2010). Comparative analysis of nonaspanin protein sequences and expression studies in zebrafish. Immunogenetics 62: 681-699.

Sun, L., Z. Meng, Y. Zhu, J. Lu, Z. Li, Q. Zhao, Y. Huang, L. Jiang, and X. Yao. (2018). TM9SF4 is a novel factor promoting autophagic flux under amino acid starvation. Cell Death Differ 25: 368-379.


TC#NameOrganismal TypeExample

TGD5 of 91 aas and 2 TMSs.  Involved in lipid transfer from TGD4 in the outer chloroplast envelope to the TGD1,2,3 ABC transporter in the inner envelope (Fan et al. 2015).

TGD5 of Arabidopsis thaliana (Mouse-ear cress)


TM9SF4 of 642 aas and 10 TMSs in a 1 (N-terminal) + 9 (1 + 2 + 2 + 2 + 2 TMS) arrangement. TM9SF4 is present in normal and leukemic hematopoietic cells, and its marked expression occurs at the level of AMLs displaying granulocytic differentiation (Paolillo et al. 2015). It promotes autophagic flux under amino acid starvation (Sun et al. 2018).

TM9SF4 of Homo sapiens


Uncharacterized protein of 77 aas and 2 TMSs, Smo4.

Smo4 of Ostreococcus lucimarinus