title: Telomerase recognizes G-quadruplex and linear DNA as distinct substrates.
abstract: Telomeric DNA can assemble into a nonlinear, higher-order conformation known as a G-quadruplex. Here, we demonstrate by electrospray ionization mass spectrometry that the two repeat telomeric sequence d(TGGGGTTGGGGT) from Tetrahymena thermophila gives rise to a novel parallel four-stranded G-quadruplex in the presence of sodium. The G-quadruplex directly interacts with the catalytic subunit of Tetrahymena telomerase (TERT) with micromolar affinity, and the presence of telomerase RNA is not obligatory for this interaction. Both N- and C-terminal halves of TERT bind the G-quadruplex independently. This G-quadruplex is a robust substrate for both recombinant and cell extract-derived telomerase in vitro. Furthermore, the G-quadruplex weakens the affinity of wild-type telomerase for the incoming nucleotide (dTTP) and likely perturbs the nucleotide binding pocket of the enzyme. In agreement with this, a lysine to alanine substitution at amino acid 538 (K538A) within motif 1 of TERT dramatically reduces the ability of telomerase to extend G-quadruplex but not linear DNA. The K538A mutant retains binding affinity for the quadruplex. This suggests that telomerase undergoes changes in conformation in its active site to specifically accommodate binding and subsequent extension of G-quadruplex DNA. We propose that telomerase recognizes G-quadruplex DNA as a substrate that is distinct from linear DNA.
authors: Children's Medical Research Institute, 214 Hawkesbury Road, Westmead NSW 2145, Australia and University of Sydney, NSW 2006, Australia.
authors: Liana
authors: L
authors: Oganesian
authors: Mark E
authors: ME
authors: Graham
authors: Phillip J
authors: PJ
authors: Robinson
authors: Tracy M
authors: TM
authors: Bryan
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D016054:DNA, Protozoan / Q000737:chemistry* / Q000378:metabolism*; D008954:Models, Biological; D009154:Mutation; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D013379:Substrate Specificity; D019098:Telomerase / Q000235:genetics / Q000378:metabolism*; D016615:Telomere / Q000235:genetics; D013768:Tetrahymena / Q000201:enzymology / Q000235:genetics
chemical_list: D016054:DNA, Protozoan; D019098:Telomerase