| Structural highlights
Function
4F2_HUMAN Required for the function of light chain amino-acid transporters. Involved in sodium-independent, high-affinity transport of large neutral amino acids such as phenylalanine, tyrosine, leucine, arginine and tryptophan. Involved in guiding and targeting of LAT1 and LAT2 to the plasma membrane. When associated with SLC7A6 or SLC7A7 acts as an arginine/glutamine exchanger, following an antiport mechanism for amino acid transport, influencing arginine release in exchange for extracellular amino acids. Plays a role in nitric oxide synthesis in human umbilical vein endothelial cells (HUVECs) via transport of L-arginine. Required for normal and neoplastic cell growth. When associated with SLC7A5/LAT1, is also involved in the transport of L-DOPA across the blood-brain barrier, and that of thyroid hormones triiodothyronine (T3) and thyroxine (T4) across the cell membrane in tissues such as placenta. Involved in the uptake of methylmercury (MeHg) when administered as the L-cysteine or D,L-homocysteine complexes, and hence plays a role in metal ion homeostasis and toxicity. When associated with SLC7A5 or SLC7A8, involved in the cellular activity of small molecular weight nitrosothiols, via the stereoselective transport of L-nitrosocysteine (L-CNSO) across the transmembrane. Together with ICAM1, regulates the transport activity LAT2 in polarized intestinal cells, by generating and delivering intracellular signals. When associated with SLC7A5, plays an important role in transporting L-leucine from the circulating blood to the retina across the inner blood-retinal barrier.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
Publication Abstract from PubMed
System x(c) (-) is an amino acid antiporter that imports L-cystine into cells and exports intracellular L-glutamate, at a 1:1 ratio. As L-cystine is an essential precursor for glutathione synthesis, system x(c) (-) supports tumor cell growth through glutathione-based oxidative stress resistance and is considered as a potential therapeutic target for cancer treatment. System x(c) (-) consists of two subunits, the light chain subunit SLC7A11 (xCT) and the heavy chain subunit SLC3A2 (also known as CD98hc or 4F2hc), which are linked by a conserved disulfide bridge. Although the recent structures of another SLC7 member, L-type amino acid transporter 1 (LAT1) in complex with CD98hc, have provided the structural basis toward understanding the amino acid transport mechanism, the detailed molecular mechanism of xCT remains unknown. To revealthe molecular mechanism, we performed single-particle analyses of the xCT-CD98hc complex. As wild-type xCT-CD98hc displayed poor stability and could not be purified to homogeneity, we applied a consensus mutagenesis approach to xCT. The consensus mutated construct exhibited increased stability as compared to the wild-type, and enabled the cryoelectron microscopy (cryo-EM) map to be obtained at 6.2 A resolution by single-particle analysis. The cryo-EM map revealed sufficient electron density to assign secondary structures. In the xCT structure, the hash and arm domains are well resolved, whereas the bundle domain shows some flexibility. CD98hc is positioned next to the xCT transmembrane domain. This study provides the structural basis of xCT, and our consensus-based strategy could represent a good choice toward solving unstable protein structures.
Consensus mutagenesis approach improves the thermal stability of system x(c) (-) transporter, xCT, and enables cryo-EM analyses.,Oda K, Lee Y, Wiriyasermkul P, Tanaka Y, Takemoto M, Yamashita K, Nagamori S, Nishizawa T, Nureki O Protein Sci. 2020 Dec;29(12):2398-2407. doi: 10.1002/pro.3966. Epub 2020 Nov 11. PMID:33016372[16]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Yanagida O, Kanai Y, Chairoungdua A, Kim DK, Segawa H, Nii T, Cha SH, Matsuo H, Fukushima J, Fukasawa Y, Tani Y, Taketani Y, Uchino H, Kim JY, Inatomi J, Okayasu I, Miyamoto K, Takeda E, Goya T, Endou H. Human L-type amino acid transporter 1 (LAT1): characterization of function and expression in tumor cell lines. Biochim Biophys Acta. 2001 Oct 1;1514(2):291-302. PMID:11557028
- ↑ Torrents D, Estevez R, Pineda M, Fernandez E, Lloberas J, Shi YB, Zorzano A, Palacin M. Identification and characterization of a membrane protein (y+L amino acid transporter-1) that associates with 4F2hc to encode the amino acid transport activity y+L. A candidate gene for lysinuric protein intolerance. J Biol Chem. 1998 Dec 4;273(49):32437-45. PMID:9829974
- ↑ Mastroberardino L, Spindler B, Pfeiffer R, Skelly PJ, Loffing J, Shoemaker CB, Verrey F. Amino-acid transport by heterodimers of 4F2hc/CD98 and members of a permease family. Nature. 1998 Sep 17;395(6699):288-91. PMID:9751058 doi:https://dx.doi.org/10.1038/26246
- ↑ Pfeiffer R, Rossier G, Spindler B, Meier C, Kuhn L, Verrey F. Amino acid transport of y+L-type by heterodimers of 4F2hc/CD98 and members of the glycoprotein-associated amino acid transporter family. EMBO J. 1999 Jan 4;18(1):49-57. PMID:9878049 doi:https://dx.doi.org/10.1093/emboj/18.1.49
- ↑ Broer A, Wagner CA, Lang F, Broer S. The heterodimeric amino acid transporter 4F2hc/y+LAT2 mediates arginine efflux in exchange with glutamine. Biochem J. 2000 Aug 1;349 Pt 3:787-95. PMID:10903140
- ↑ Broer A, Friedrich B, Wagner CA, Fillon S, Ganapathy V, Lang F, Broer S. Association of 4F2hc with light chains LAT1, LAT2 or y+LAT2 requires different domains. Biochem J. 2001 May 1;355(Pt 3):725-31. PMID:11311135
- ↑ Ritchie JW, Taylor PM. Role of the System L permease LAT1 in amino acid and iodothyronine transport in placenta. Biochem J. 2001 Jun 15;356(Pt 3):719-25. PMID:11389679
- ↑ Friesema EC, Docter R, Moerings EP, Verrey F, Krenning EP, Hennemann G, Visser TJ. Thyroid hormone transport by the heterodimeric human system L amino acid transporter. Endocrinology. 2001 Oct;142(10):4339-48. PMID:11564694
- ↑ Okamoto Y, Sakata M, Ogura K, Yamamoto T, Yamaguchi M, Tasaka K, Kurachi H, Tsurudome M, Murata Y. Expression and regulation of 4F2hc and hLAT1 in human trophoblasts. Am J Physiol Cell Physiol. 2002 Jan;282(1):C196-204. PMID:11742812
- ↑ Simmons-Willis TA, Koh AS, Clarkson TW, Ballatori N. Transport of a neurotoxicant by molecular mimicry: the methylmercury-L-cysteine complex is a substrate for human L-type large neutral amino acid transporter (LAT) 1 and LAT2. Biochem J. 2002 Oct 1;367(Pt 1):239-46. PMID:12117417 doi:https://dx.doi.org/10.1042/BJ20020841
- ↑ Kim DK, Kanai Y, Choi HW, Tangtrongsup S, Chairoungdua A, Babu E, Tachampa K, Anzai N, Iribe Y, Endou H. Characterization of the system L amino acid transporter in T24 human bladder carcinoma cells. Biochim Biophys Acta. 2002 Sep 20;1565(1):112-21. PMID:12225859
- ↑ Arancibia-Garavilla Y, Toledo F, Casanello P, Sobrevia L. Nitric oxide synthesis requires activity of the cationic and neutral amino acid transport system y+L in human umbilical vein endothelium. Exp Physiol. 2003 Nov;88(6):699-710. PMID:14603368
- ↑ Liu X, Charrier L, Gewirtz A, Sitaraman S, Merlin D. CD98 and intracellular adhesion molecule I regulate the activity of amino acid transporter LAT-2 in polarized intestinal epithelia. J Biol Chem. 2003 Jun 27;278(26):23672-7. Epub 2003 Apr 25. PMID:12716892 doi:https://dx.doi.org/10.1074/jbc.M302777200
- ↑ Tomi M, Mori M, Tachikawa M, Katayama K, Terasaki T, Hosoya K. L-type amino acid transporter 1-mediated L-leucine transport at the inner blood-retinal barrier. Invest Ophthalmol Vis Sci. 2005 Jul;46(7):2522-30. PMID:15980244 doi:https://dx.doi.org/10.1167/iovs.04-1175
- ↑ Li S, Whorton AR. Identification of stereoselective transporters for S-nitroso-L-cysteine: role of LAT1 and LAT2 in biological activity of S-nitrosothiols. J Biol Chem. 2005 May 20;280(20):20102-10. Epub 2005 Mar 15. PMID:15769744 doi:https://dx.doi.org/10.1074/jbc.M413164200
- ↑ Oda K, Lee Y, Wiriyasermkul P, Tanaka Y, Takemoto M, Yamashita K, Nagamori S, Nishizawa T, Nureki O. Consensus mutagenesis approach improves the thermal stability of system x(c) (-) transporter, xCT, and enables cryo-EM analyses. Protein Sci. 2020 Dec;29(12):2398-2407. PMID:33016372 doi:10.1002/pro.3966
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