Structural insights into Pot1-ssDNA, Pot1-Tpz1 and Tpz1-Ccq1 Interactions within fission yeast shelterin complex

Abstract

The conserved shelterin complex caps chromosome ends to protect telomeres and regulate telomere replication. In fission yeast Schizosaccharomyces pombe, shelterin consists of telomeric single- and double-stranded DNA-binding modules Pot1-Tpz1 and Taz1-Rap1 connected by Poz1, and a specific component Ccq1. While individual structures of the two DNA-binding OB folds of Pot1 (Pot1OB1-GGTTAC and Pot1OB2-GGTTACGGT) are available, structural insight into recognition of telomeric repeats with spacers by the complete DNA-binding domain (Pot1DBD) remains an open question. Moreover, structural information about the Tpz1-Ccq1 interaction requires to be revealed for understanding how the specific component Ccq1 of S. pombe shelterin is recruited to telomeres to function as an interacting hub. Here, we report the crystal structures of Pot1DBD-single-stranded-DNA, Pot1372-555-Tpz1185-212 and Tpz1425-470-Ccq1123-439 complexes and propose an integrated model depicting the assembly mechanism of the shelterin complex at telomeres. The structure of Pot1DBD-DNA unveils how Pot1 recognizes S. pombe degenerate telomeric sequences. Our analyses of Tpz1-Ccq1 reveal structural basis for the essential role of the Tpz1-Ccq1 interaction in telomere recruitment of Ccq1 that is required for telomere maintenance and telomeric heterochromatin formation. Overall, our findings provide valuable structural information regarding interactions within fission yeast shelterin complex at 3’ ss telomeric overhang.

Condensin positioning at telomeres by shelterin proteins drives sister-telomere disjunction in anaphase

“…This is a remarkable conserved structural feature between the shelterin of S. pombe and the human shelterin. Notably, it was recently shown that the telomeric components of S. pombe can dimerize leading to a higher complex organization of the shelterin (Sun et al , 2022). It is thus likely that dimerization of Taz1, Poz1, and the Tpz1-Ccq1 subcomplex may also contribute to the clustering of sister and non-sister chromatid telomeres.…”

Telomere-to-Telomere genome assemblies of human-infecting Encephalitozoon species

“…Telomere maintenance proteins encoded in Encephalitozoon spp. include the telomerase reverse transcriptase (Trt1/TERT) and RNA polymerase II CTD phosphatase Ssu72 required for telomere length regulation [ 33 ], proteins Stn1 and Ten1 from the Cdc13-Stn1-Ten1 (CST) telomere capping complex [ 34 ], proteins Pot1 and Tpz1 from the shelterin complex protecting telomeres from degradation [ 35 ], and proteins Rad32 (Mre11 in S. cerevisiae ) and Rad50 from the S. pombe Rad32-Rad50-Nbs1 complex, a multifunctional complex involved in G-quadruplex binding and in DNA double strand break repair [ 36 ]. Heterochromatin formation proteins encoded in the Encephalitozoon genomes include heterochromatin protein Swi6 (HP1 in humans), a transcriptional repressor that regulates lysine 9 methylation on histone H3 residues [ 37 ], subunits Spt16 and Pob3 from the histone chaperone FACT (FAcilitates Chromatin Transcription) required for constitutive heterochromatin formation [ 38 ], chromatin-remodeling ATPase INO80 whose associated complex regulates heterochromatin inheritance [ 39 ], the origin recognition complex protein 1 (Orp1/ORC1) essential to heterochromatin formation in humans [ 40 ], and the histone H3 lysine modification protein Clr4 (cryptic loci regulator 4), which regulates gene expression via chromatin interaction and increases spontaneous mutations rates in fungi [ 41 ].…”

Condensin positioning at telomeres by shelterin proteins drives sister-telomere disjunction in anaphase

“…This is a remarkable conserved structural feature between the shelterin of S. pombe and the human shelterin. Recently the group of M. Lei showed that some of the telomeric components of S. pombe can dimerize leading to a higher complex organization of the shelterin (Sun et al, 2022). It is likely that dimerization of Taz1, Poz1, and the Tpz1-Ccq1 subcomplex may also contribute to the clustering of sister and non-sister chromatid telomeres.…”