| Structural highlights
Disease
[TNPO3_HUMAN] Primary biliary cirrhosis;Autosomal dominant limb-girdle muscular dystrophy type 1F.
Function
[TNPO3_HUMAN] Seems to function in nuclear protein import as nuclear transport receptor. In vitro, mediates the nuclear import of splicing factor SR proteins RBM4, SFRS1 and SFRS2, by recognizing phosphorylated RS domains.[1] [2] [3] [4] [SRSF1_HUMAN] Plays a role in preventing exon skipping, ensuring the accuracy of splicing and regulating alternative splicing. Interacts with other spliceosomal components, via the RS domains, to form a bridge between the 5'- and 3'-splice site binding components, U1 snRNP and U2AF. Can stimulate binding of U1 snRNP to a 5'-splice site-containing pre-mRNA. Binds to purine-rich RNA sequences, either the octamer, 5'-RGAAGAAC-3' (r=A or G) or the decamers, AGGACAGAGC/AGGACGAAGC. Binds preferentially to the 5'-CGAGGCG-3' motif in vitro. Three copies of the octamer constitute a powerful splicing enhancer in vitro, the ASF/SF2 splicing enhancer (ASE) which can specifically activate ASE-dependent splicing. Isoform ASF-2 and isoform ASF-3 act as splicing repressors.[5] [6]
Publication Abstract from PubMed
Transportin 3 (Tnpo3, Transportin-SR2) is implicated in nuclear import of splicing factors and HIV-1 replication. Herein, we show that the majority of cellular Tnpo3 binding partners contain arginine-serine (RS) repeat domains and present crystal structures of human Tnpo3 in its free as well as GTPase Ran- and alternative splicing factor/splicing factor 2 (ASF/SF2)-bound forms. The flexible beta-karyopherin fold of Tnpo3 embraces the RNA recognition motif and RS domains of the cargo. A constellation of charged residues on and around the arginine-rich helix of Tnpo3 HEAT repeat 15 engage the phosphorylated RS domain and are critical for the recognition and nuclear import of ASF/SF2. Mutations in the same region of Tnpo3 impair its interaction with the cleavage and polyadenylation specificity factor 6 (CPSF6) and its ability to support HIV-1 replication. Steric incompatibility of the RS domain and RanGTP engagement by Tnpo3 provides the mechanism for cargo release in the nucleus. Our results elucidate the structural bases for nuclear import of splicing factors and the Tnpo3-CPSF6 nexus in HIV-1 biology.
Structural basis for nuclear import of splicing factors by human Transportin 3.,Maertens GN, Cook NJ, Wang W, Hare S, Gupta SS, Oztop I, Lee K, Pye VE, Cosnefroy O, Snijders AP, Kewalramani VN, Fassati A, Engelman A, Cherepanov P Proc Natl Acad Sci U S A. 2014 Jan 21. PMID:24449914[7]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
See Also
References
- ↑ Kataoka N, Bachorik JL, Dreyfuss G. Transportin-SR, a nuclear import receptor for SR proteins. J Cell Biol. 1999 Jun 14;145(6):1145-52. PMID:10366588
- ↑ Lai MC, Lin RI, Huang SY, Tsai CW, Tarn WY. A human importin-beta family protein, transportin-SR2, interacts with the phosphorylated RS domain of SR proteins. J Biol Chem. 2000 Mar 17;275(11):7950-7. PMID:10713112
- ↑ Lai MC, Lin RI, Tarn WY. Transportin-SR2 mediates nuclear import of phosphorylated SR proteins. Proc Natl Acad Sci U S A. 2001 Aug 28;98(18):10154-9. Epub 2001 Aug 21. PMID:11517331 doi:http://dx.doi.org/10.1073/pnas.181354098
- ↑ Lai MC, Kuo HW, Chang WC, Tarn WY. A novel splicing regulator shares a nuclear import pathway with SR proteins. EMBO J. 2003 Mar 17;22(6):1359-69. PMID:12628928 doi:http://dx.doi.org/10.1093/emboj/cdg126
- ↑ Zuo P, Manley JL. Functional domains of the human splicing factor ASF/SF2. EMBO J. 1993 Dec;12(12):4727-37. PMID:8223481
- ↑ Kohtz JD, Jamison SF, Will CL, Zuo P, Luhrmann R, Garcia-Blanco MA, Manley JL. Protein-protein interactions and 5'-splice-site recognition in mammalian mRNA precursors. Nature. 1994 Mar 10;368(6467):119-24. PMID:8139654 doi:http://dx.doi.org/10.1038/368119a0
- ↑ Maertens GN, Cook NJ, Wang W, Hare S, Gupta SS, Oztop I, Lee K, Pye VE, Cosnefroy O, Snijders AP, Kewalramani VN, Fassati A, Engelman A, Cherepanov P. Structural basis for nuclear import of splicing factors by human Transportin 3. Proc Natl Acad Sci U S A. 2014 Jan 21. PMID:24449914 doi:http://dx.doi.org/10.1073/pnas.1320755111
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