Clear view of telomerase at last

The enzyme telomerase, which restores chromosome ends shortened by cell division, was discovered over three decades ago, but no view of the human enzyme at atomic resolution, approximately 3 Å, has been captured. The problem is that telomerase is present in cells in tiny quantities and is not easily purified. Now, using refined purification methods, Kathleen Collins, Eva Nogales, Kelly Nguyen, and coworkers at the University of California, Berkeley, have taken a giant leap toward the atomic-resolution goal (Nature 2018, DOI: 10.1038/s41586-018-0062-x). With cryo-electron microscopy, they analyzed the enzyme at 7 to 8 Å. A previous 30 Å electron microscopy structure was so fuzzy that it left the components of telomerase’s two lobes uncertain. The new structure reveals that one lobe, the catalytic core, contains telomerase reverse transcriptase, which catalyzes DNA addition to chromosome end-caps, and telomerase RNA, which templates the addition and links the two lobes. The second lobe, called H/ACA, which plays regulatory and structural roles, contains two heterotetrameric H/ACA proteins and the Cajal body protein TCAB1. Telomerase inhibitors haven’t done well in cancer clinical trials, says Jerry W. Shay of the University of Texas Southwestern Medical Center, but the new study could lead to “new ways to target telomerase in cancer and to elongate telomeres as part of regenerative medicine.” The Berkeley researchers’ next step?—3 to 4 Å resolution, they hope.