Single molecule FRET-Rosetta reveals RNA structural rearrangements during human telomerase catalysis

Abstract

Maintenance of telomeres by telomerase permits continuous proliferation of rapidly dividing cells, including the majority of human cancers. Despite its direct biomedical significance, the architecture of the human telomerase complex remains unknown. Generating homogeneous telomerase samples has presented a significant barrier to developing improved structural models. Here we pair single molecule Förster Resonance Energy Transfer (smFRET) measurements with Rosetta modeling to map the conformations of the essential telomerase RNA pseudoknot domain within the active ribonucleoprotein. FRET-guided modeling places the essential pseudoknot fold distal to the active site on a protein surface comprising the C-Terminal Element, a domain that shares structural homology with canonical polymerase thumb domains. An independently solved medium-resolution structure of Tetrahymena telomerase provided a powerful blind test of our modeling methodology and sheds light on the structural homology of this domain across diverse organisms. Surprisingly, our smFRET-Rosetta models reveal nanometer-scale rearrangements in the pseudoknot domain during catalysis. Taken together, our FRET data and pseudo-atomic molecular models permit us to propose a possible mechanism for how pseudoknot domain rearrangement is coupled to template hybrid elongation.