Structural and functional analysis of the human POT1-TPP1 telomeric complex

Abstract

POT1 and TPP1 are part of the shelterin complex and are essential for telomere length regulation and maintenance. Naturally occurring mutations of the telomeric POT1–TPP1 complex are implicated in familial glioma, melanoma and chronic lymphocytic leukaemia. Here we report the atomic structure of the interacting portion of the human telomeric POT1–TPP1 complex and suggest how several of these mutations contribute to malignant cancer. The POT1 C-terminus (POT1C) forms a bilobal structure consisting of an OB-fold and a holiday junction resolvase domain. TPP1 consists of several loops and helices involved in extensive interactions with POT1C. Biochemical data shows that several of the cancer-associated mutations, partially disrupt the POT1–TPP1 complex, which affects its ability to bind telomeric DNA efficiently. A defective POT1–TPP1 complex leads to longer and fragile telomeres, which in turn promotes genomic instability and cancer.

Human POT1 Prevents Severe Telomere Instability Induced by Homology Directed DNA Repair

“…The POT1 protein contains two OB-folds in its N-terminal half with which it binds single stranded telomeric DNA (Lei et al, 2004). The C-terminal half contains a third split OBfold which is bound by TPP1 via multiple interactions (Chen et al, 2017;Rice et al, 2017). For telomere recruitment, the interaction of POT1 with TPP1 is necessary and sufficient (Liu et al, 2004;Pinzaru et al, 2016;Ye et al, 2004).…”

Human CST Prefers G-Rich but Not Necessarily Telomeric Sequences

“…8 TPP1 interacts with the C-terminal domain of POT1, providing a bridge to the double-stranded DNA telomere-binding factors while also increasing the avidity of POT1 for single-stranded telomeric sequences. 4,7,9,10 …”

Structural biology of telomerase and its interaction at telomeres

“…The ciliate Sterkiella nova (formerly Oxytricha nova ) telomere end-binding proteins TEBPα and TEBPβ [65] were subsequently identified as POT1 and TPP1 homologues, respectively, based on the crystal structures [66,67]. Two crystal structures of human POT1 C-terminal domain in complex with TPP1 POT1-binding motif (PBM) were recently reported [16,17]. POT1C has an unusual architecture consisting of an OB-fold (OB3) that includes a Zn +2 -ribbon motif and a Holliday junction resolvase (HJR)-like domain, formed from an insertion in the C-terminal end of the primary sequence, that pack tightly against one another.…”

“…POT1C has an unusual architecture consisting of an OB-fold (OB3) that includes a Zn +2 -ribbon motif and a Holliday junction resolvase (HJR)-like domain, formed from an insertion in the C-terminal end of the primary sequence, that pack tightly against one another. In the complex, TPP1 PBM (residues 255-337), which forms 4 helices connected by structured linkers, interacts extensively with both domains (Figure 4f) [17]. Based on the crystal structure of the Oxytricha nova TEBPα–β–ssDNA complex and SAXS data on the TPP1-POT1 complex, the overall architecture of the POT1–TPP1 complex has also been modeled (Figure 4f) [16].…”

“…Somewhat more rapid structural progress had been made with telomere binding proteins, especially from yeasts [12]. During the past couple of years, a surge of progress has been made on structural biology of telomerase, including reports of the first cryo-electron microscopy (cryo-EM) structure of telomerase, from Tetrahymena [13], crystal structures of TERT and TERT-interacting protein domains [14–17], telomerase RNA structures and models [18,19], and identification in Tetrahymena telomerase holoenzyme of human homologues of telomere-associated proteins [13,20] that have provided a more unified view of telomerase interaction at telomeres [21]. Here we review these and other studies published since 2015 on structural investigations of primarily Tetrahymena and vertebrate telomerase and its interaction at telomeres.…”