Abstract
Telomeres are nucleoprotein complexes that play essential roles in protecting chromosome ends. Mammalian telomeres consist of repetitive DNA sequences bound by the shelterin complex. In this complex, the POT1-TPP1 heterodimer binds to single-stranded telomeric DNAs, while TRF1 and TRF2-RAP1 interact with double-stranded telomeric DNAs. TIN2, the linchpin of this complex, simultaneously interacts with TRF1, TRF2, and TPP1 to mediate the stable assembly of the shelterin complex. However, the molecular mechanism by which TIN2 interacts with these proteins to orchestrate telomere protection remains poorly understood. Here, we report the crystal structure of the N-terminal domain of TIN2 in complex with TIN2-binding motifs from TPP1 and TRF2, revealing how TIN2 interacts cooperatively with TPP1 and TRF2. Unexpectedly, TIN2 contains a telomeric repeat factor homology (TRFH)-like domain that functions as a protein-protein interaction platform. Structure-based mutagenesis analyses suggest that TIN2 plays an important role in maintaining the stable shelterin complex required for proper telomere end protection.
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Acknowledgements
We thank staffs from BL18U1 and BL19U1 beamlines at NCPSS and Shanghai Synchrotron Radiation Facility (SSRF) for their help with crystal data collection. We are extremely grateful to National Center for Protein Sciences Shanghai (Protein Expression and Purification system, NMR system) for their instrument support and technical assistance. This work was supported by grants from the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB08010201) to ML and YC, the Ministry of Science and Technology of China (2013CB910401 to YC,2013CB910402 to ML), the National Natural Science Foundation of China (31470737 and 31670748 to YC, 31330040 and 31525007 to ML), the Basic Research Project of Shanghai Science and Technology Commission (14JC1407200 to YC), and NCI (RO1 CA129037, RO1CA202816, R21CA200506, and R21CA182280) to SC.
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( Supplementary information is linked to the online version of the paper on the Cell Research website.)
Supplementary information
Supplementary information, Figure S1
Mapping interaction domains between TRF2-TIN2 and TPP1-TIN2. (PDF 443 kb)
Supplementary information, Figure S2
The crystal structure of TIN2TRFH-TPP1TBM-TRF2TBM complex. (PDF 2180 kb)
Supplementary information, Figure S3
Analyses of TIN2 localization in U2OS cells. (PDF 140 kb)
Supplementary information, Figure S4
TIN2 protects telomeres from engaging in DNA damage responses. (PDF 205 kb)
Supplementary information, Figure S5
TIN2 interaction with shelterin components is required to prevent chromosome fusions. (PDF 2125 kb)
Supplementary information, Figure S6
TIN2TRFH shows distinct properties compared with TRF2TRFH. (PDF 854 kb)
Supplementary information, Figure S7
TIN2132-188 is crucial for both TRF2 and TPP1 interactions, and also maintains the correct fold of TIN2TRFH. (PDF 153 kb)
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Hu, C., Rai, R., Huang, C. et al. Structural and functional analyses of the mammalian TIN2-TPP1-TRF2 telomeric complex. Cell Res 27, 1485–1502 (2017). https://doi.org/10.1038/cr.2017.144
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DOI: https://doi.org/10.1038/cr.2017.144
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