Telomeres, the repetitive DNA-protein complexes at the ends of linear chromosomes, shorten with each cycle of DNA replication, providing a counting mechanism to limit the number of times a cell can divide. Most cancer cells have activated the ribonucleoprotein enzyme telomerase to add telomeric DNA repeats and thereby counteract telomere shortening, allowing for unlimited proliferation. In contrast, normal cells have undetectable or very low levels of telomerase. The development of telomerase inhibitors through structure-guided design holds promise as an effective anticancer therapy.

In 2007 we reported the purification and molecular composition of the core telomerase enzyme complex, consisting of two copies each of the Telomerase Reverse Transcriptase catalytic protein, telomerase RNA, and the RNA-binding protein dyskerin. Building on this knowledge, we have developed an overexpression system that provides ≥10³-fold greater active telomerase complex over endogenous levels through transient co-transfection of all three genes. Telomerase overexpression is carried out in suspension-phase HEK293T cells in 20-L bioreactors, followed by selective purification of enzymatically active complexes. This system has provided sufficient telomerase to obtain negative-stain electron microscopy (EM) data, revealing a bi-lobal dimeric structure. Current efforts are directed towards cryo-EM to obtain data of potentially higher resolution and a more native solution-phase structure.