TGD4 involved in endoplasmic reticulum-to-chloroplast lipid trafficking is a phosphatidic acid binding protein

Journal Article · Tue May 01 04:00:00 EDT 2012 · The Plant Journal

DOI:https://doi.org/10.1111/j.1365-313X.2012.04900.x· OSTI ID:1049242

Wang, Z; Xu, C; Benning, C

The synthesis of galactoglycerolipids, which are prevalent in photosynthetic membranes, involves enzymes at the endoplasmic reticulum (ER) and the chloroplast envelope membranes. Genetic analysis of trigalactosyldiacylglycerol (TGD) proteins in Arabidopsis has demonstrated their role in polar lipid transfer from the ER to the chloroplast. The TGD1, 2, and 3 proteins resemble components of a bacterial-type ATP-binding cassette (ABC) transporter, with TGD1 representing the permease, TGD2 the substrate binding protein, and TGD3 the ATPase. However, the function of the TGD4 protein in this process is less clear and its location in plant cells remains to be firmly determined. The predicted C-terminal {beta}-barrel structure of TGD4 is weakly similar to proteins of the outer cell membrane of Gram-negative bacteria. Here, we show that, like TGD2, the TGD4 protein when fused to DsRED specifically binds phosphatidic acid (PtdOH). As previously shown for tgd1 mutants, tgd4 mutants have elevated PtdOH content, probably in extraplastidic membranes. Using highly purified and specific antibodies to probe different cell fractions, we demonstrated that the TGD4 protein was present in the outer envelope membrane of chloroplasts, where it appeared to be deeply buried within the membrane except for the N-terminus, which was found to be exposed to the cytosol. It is proposed that TGD4 is either directly involved in the transfer of polar lipids, possibly PtdOH, from the ER to the outer chloroplast envelope membrane or in the transfer of PtdOH through the outer envelope membrane.

• Research Organization: BROOKHAVEN NATIONAL LABORATORY (BNL)
• Sponsoring Organization: USDOE SC OFFICE OF BASIC ENERGY SCIENCES
• DOE Contract Number: AC02-98CH10886
• OSTI ID: 1049242
• Report Number(s): BNL--96932-2012-JA; KC0304000
• Journal Information: The Plant Journal, Journal Name: The Plant Journal Journal Issue: 4 Vol. 70; ISSN 0960-7412
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
60 APPLIED LIFE SCIENCES
ANTIBODIES
ARABIDOPSIS
Arabidopsis thaliana
BACTERIA
CELL MEMBRANES
CHLOROPLASTS
ENDOPLASMIC RETICULUM
ENZYMES
GENETICS
LIPIDS
MEMBRANES
MUTANTS
PHOTOSYNTHETIC MEMBRANES
PLANT CELLS
PROBES
PROTEINS
SUBSTRATES
SYNTHESIS
beta-barrel protein
chloroplast
envelope membrane
lipid transport
lipids