Poster Presentation The 48th Lorne Conference on Protein Structure and Function 2023

Functional interaction between compound heterozygous TERT mutations causes severe Telomere Biology Disorder (#426)

Jia Q Truong 1 , Aram Niaz 2 , Jessica K Holien 1 , Scott B Cohen 3 , Tracy M Bryant 3
  1. School of Science, STEM College , RMIT University, Bundoora, Victoria, Australia
  2. Rare Diseases Functional Genomics, Kids Research, The Children's Hospital at Westmead and Children's Medical Research Institute, Westmead, NSW, Australia
  3. Children’s Medical Research Institute, Faculty of Medicine and Health, University of Sydney, Westmead, New South Wales, Australia

Telomere biology disorders (TBD) are a set of syndromes characterised by short telomeres, that can manifest in presentations such as dyskeratosis congenta, idiopathic pulmonary fibrosis and aplastic anaemia. TBD arises from germline mutations in genes involved in maintaining telomeres, such as telomerase. As a result, study of disease-associated mutations in telomerase can be a fruitful source of insight into the biochemical mechanism of telomerase. Our previous studies of mutations in telomerase have allowed the identification of a motif involved in DNA binding, regions of enzymatic conformational change (1) and mechanisms of DNA binding (2).

In this study (3), we describe a patient carrying compound heterozygous variants in the TERT gene (L557P and K1050E), which encodes the catalytic subunit of telomerase, hTERT. This patient presented with an extremely severe Hoyeraal-Hreidarsson form of TBD, although his heterozygous parents are clinically unaffected. Molecular dynamic simulations and kinetic analyses show that hTERTL557P has reduced association with the RNA component of telomerase hTR, and hTERTK1050E has reduced binding to its DNA substrate and reduced enzyme processivity in adding telomeric repeats. Most interestingly, we demonstrate a functional interaction between telomerase proteins encoded by different alleles. WT hTERT, but not hTERTL557P, rescues the processivity defect of hTERTK1050E. The results demonstrate that RNA binding to one telomerase molecule can affect processivity in another telomerase molecule. This result highlights the need to study compound heterozygous variants of telomerase in combination, as interallelic effects may be difficult to predict. These methods are also vitally important for accurate molecular diagnosis of TBD patients.

References

  1. Tomlinson CG, Holien JK, Mathias JAT, Parker MW, Bryan TM. The C-terminal extension of human telomerase reverse transcriptase is necessary for high affinity binding to telomeric DNA. Biochimie. 2016;128-129:114-21.
  2. Tomlinson CG, Moye AL, Holien JK, Parker MW, Cohen SB, Bryan TM. Two-step mechanism involving active-site conformational changes regulates human telomerase DNA binding. Biochem J. 2015;465(2):347-57.
  3. Niaz A, Truong JQ, Manoleras A, Fox L, Blombery P, Vasireddy RS, et al. Functional interaction between compound heterozygous TERT mutations causes severe telomere biology disorder. Blood Advances. 2022.