Structural and functional analyses of the mammalian TIN2-TPP1-TRF2 telomeric complex

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.

Human telomere repeat binding factor TRF1 replaces TRF2 bound to shelterin core hub TIN2 when TPP1 is absent

“…We wanted to know whether TIN2 can accommodate both TRF1 and TRF2 simultaneously. According to previous measurements of Hu et al and Chen et al 28,29 along with our MST assays (Figure 2-figure supplement 2) we allowed to form stable complexes of TRF1-TIN2 and TRF2-TIN2 at micromolar concentrations. We prepared protein complexes in 2:1 stoichiometry for TRF1 or TRF2 and TIN2 according to Lim et al 27 , in all experiments within this study.…”

“…Previous studies described the structure and binding affinity of peptides representing interaction regions that take part in TRF1 and TRF2 binding to TIN2 28 . Very recently, the structure of the isolated interacting domains of TRF2, TIN2 and TPP1 has been determined 29 .…”

TERT and TERC mutations detected in cryptic dyskeratosis congenita suppress telomerase activity

“…6 Shelterin complexes, on the other hand, act in part to form and protect the characteristic structure of the telomere terminal. 7 A wide range of gene mutations that cause abnormalities within the telomerase complex have been reported. [8][9][10][11][12][13][14][15][16][17] cDKC is thought to develop when there is a low degree to which telomere-related gene mutations impair telomere correction, and generational anticipation and aging are not far advanced.…”

CTC1‐STN1 coordinates G‐ and C‐strand synthesis to regulate telomere length

“…The TTAGGG repeat binding factors, Telomere Recognition Factor 1 (TRF1) and Telomere Recognition Factor 2: Repressor/Activator binding Protein 1 (TRF2:RAP1), bind to the duplex portion of telomeric DNA. The Protection of Telomere 1 (POT1) protein interacts with the ss telomeric overhang and forms a heterodimer with TPP1 (a consensus name derived from the three competing acronyms TINT1, PTOP, and PIP1), while TRF1‐Interacting nuclear protein 2 (TIN2), the linchpin of this complex, bridges TPP1:POT1 with TRF1:TRF2:RAP1 (Hu et al., 2017). Shelterin components function to repress distinct DNA damage response and repair pathways at telomeres.…”