2.A.126 The Fatty Acid Exporter (FAX) Family

Fatty acid synthesis in plants occurs in plastids, and these compounds are exported for subsequent acyl editing and lipid assembly in the cytosol and endoplasmatic reticulum. Li et al. 2015 identified FAX1 (fatty acid export 1) in the chloroplast inner envelope. FAX1 mutants in Arabidopsis thaliana are deficient for biomass production, male fertility and synthesis of fatty acid-derived compounds such as lipids, ketone waxes, and pollen cell wall materials. Determination of lipid, fatty acid and wax contents revealed that endoplasmatic reticulum (ER)-derived lipids decreased when FAX1 was missing, but levels of several plastid-produced species increased. fax1 over-expression gave the opposite behavior, including a pronounced increase of triacyglycerol oils in flowers and leaves.The cuticular layer of stems from fax1 knockout lines was reduced in C29 ketone wax compounds. Since in yeast, FAX1 could complement fatty acid transport defects, Li et al. 2015 concluded that FAX1 mediates fatty acid export from plastids. In vertebrates, FAX1 homologues are related mitochondrial membrane proteins.


 

References:

Li, N., I.L. Gügel, P. Giavalisco, V. Zeisler, L. Schreiber, J. Soll, and K. Philippar. (2015). FAX1, a novel membrane protein mediating plastid fatty acid export. PLoS Biol 13: e1002053.

Liu, J., W. Liu, L. Yang, Q. Wu, H. Zhang, A. Fang, L. Li, X. Xu, L. Sun, J. Zhang, F. Tang, and X. Wang. (2017). The Primate-Specific Gene TMEM14B Marks Outer Radial Glia Cells and Promotes Cortical Expansion and Folding. Cell Stem Cell 21: 635-649.e8.

Steensma, D.P., M. Wermke, V.M. Klimek, P.L. Greenberg, P. Font, R.S. Komrokji, J. Yang, A.M. Brunner, H.E. Carraway, L. Ades, A. Al-Kali, J.M. Alonso-Dominguez, A. Alfonso-Piérola, C.C. Coombs, H.J. Deeg, I. Flinn, J.M. Foran, G. Garcia-Manero, M.B. Maris, M. McMasters, J.B. Micol, J.P. De Oteyza, F. Thol, E.S. Wang, J.M. Watts, J. Taylor, R. Stone, V. Gourineni, A.J. Marino, H. Yao, B. Destenaves, X. Yuan, K. Yu, S. Dar, L. Ohanjanian, K. Kuida, J. Xiao, C. Scholz, A. Gualberto, and U. Platzbecker. (2021). Phase I First-in-Human Dose Escalation Study of the oral SF3B1 modulator H3B-8800 in myeloid neoplasms. Leukemia. [Epub: Ahead of Print]

Woo, I.S., H. Jin, E.S. Kang, H.J. Kim, J.H. Lee, K.C. Chang, J.Y. Park, W.S. Choi, and H.G. Seo. (2011). TMEM14A inhibits N-(4-hydroxyphenyl)retinamide-induced apoptosis through the stabilization of mitochondrial membrane potential. Cancer Lett 309: 190-198.

Examples:

TC#NameOrganismal TypeExample
2.A.126.1.1

Tmemb_14 family protein of 4 TMSs.  Show some sequence similarity with 2.A.7.26.3

Chlamidiae

Tmemb_14 protein of Prarchlamydia acanthamoebae

 
2.A.126.1.10

Uncharacterized protein of 116 aas

Euglenozoa

UP of Trypanosoma brucei

 
2.A.126.1.11

Uncharacterized protein of 105 aas and 4 TMSs

UP of Naumovozyma dairenensis (Saccharomyces dairenensis)

 
2.A.126.1.12

Uncharacterized protein of 116 aas

Planctomycetes

UP of Isophaera pallida

 
2.A.126.1.13

Uncharacterized protein of 105 aas and 4 TMSs

UP of Trypanosoma vivax

 
2.A.126.1.14

Putative MDR efflux pump of 153 aas and 4 TMSs

Putative porter of Zea mays (Maize)

 
2.A.126.1.15

Uncharacterized protein of 125 aas and 4 TMSs

UP of Nostoc punctiforme

 
2.A.126.1.16

Chloroplast fatty acid export 2 protein FAX2 of 240 aas and 4 TMSs.

FAX2 of Arabidopsis thaliana

 
2.A.126.1.17

Uncharacterized protein of 129 aas

Alveolata

UP of Babesia equi

 
2.A.126.1.18

Transmembrane Protein 14C (TMEM14C) of 112 aas and 4 TMSs. It is a mitochondrial porphyrin (protoporphyrinogen) transporter, essential for haem biosynthesis. It is an SF3B1 splicing target (Steensma et al. 2021).

TMEM14C of Homo sapiens

 
2.A.126.1.19

TMEM14A of 99 aas and 4 TMSs. It inhibits apoptosis via negative regulation of the mitochondrial outer membrane permeabilization involved in the apoptotic signaling pathway (). It inhibits N-(4-hydroxyphenyl)retinamide-induced apoptosis through the stabilization of the mitochondrial membrane potential (Woo et al. 2011).

TMEM14A of Homo sapiens

 
2.A.126.1.2

Uncharacterized protein of 105 aas

Amoeba

UP of Acanthamoeba castellanii

 
2.A.126.1.20

TMEM14B of 114 aas and 4 TMSs.  It is a primate-specific protein involved in cortical expansion and folding in the developing neocortex. It may drive neural progenitor proliferation through nuclear translocation of IQGAP1, which in turn promotes G1/S cell cycle transitions (Liu et al. 2017).

TMEM14B of Homo sapiens

 
2.A.126.1.3

Uncharacterized protein of 104 aas

Cyanobacteria

UP of Anabaena cylindrica

 
2.A.126.1.4

Uncharacterized protein of 102 aas

Slime molds

UP of Dictyostelium discoideum

 
2.A.126.1.5

Uncharacterized protein of 111 aas

Insects

UP of Bombyx mori

 
2.A.126.1.6

Uncharacterized protein of 114 aas and 4 TMSs, TMEM14DP or TMEM14D.

Animals

UP of Homo sapiens

 
2.A.126.1.7

Uncharacterized protein of 166 aas with 4 TMSs and an N-terminal hydrophilic extension

Algae

UP of Galdieria sulfuraria

 
2.A.126.1.8

Tmem_14 protein of 110 aas

Fungi

UP of Candida albicans

 
2.A.126.1.9

Uncharacterized protein of 104 aas

Fungi

UP of Chaetomium globosum

 
Examples:

TC#NameOrganismal TypeExample
2.A.126.2.1

Uncharacterized protein of 120 aas

Green algae

UP of Micromonas pusilla

 
2.A.126.2.2

Uncharacterized protein of 220 aas with 4 TMSs and an N-terminal hydrophilic extension

Plants

UP of Capsella rubella

 
2.A.126.2.3

Uncharacterized protein of 120 aas and 4 TMSs

UP of Chlorella variabilis (Green alga)

 
2.A.126.2.4

Plastid fatty acid export protein 1, FAX1, of 226 aas and 4 TMSs with an N-terminal hydrophlic domain (Li et al. 2015).

FAX1 of Arabidopsis thaliana

 
Examples:

TC#NameOrganismal TypeExample