Structural and biochemical basis for DNA and RNA catalysis by human Topoisomerase 3β
Xi Yang, Sourav Saha, Wei Yang, Keir C. Neuman, Yves Pommier
Abstract
In metazoans, topoisomerase 3β (TOP3B) regulates R-loop dynamics and mRNA translation, which are critical for genome stability, neurodevelopment and normal aging. As a Type IA topoisomerase, TOP3B acts by general acid-base catalysis to break and rejoin single-stranded DNA. Passage of a second DNA strand through the transient break permits dissipation of hypernegative DNA supercoiling and catenation/knotting. Additionally, hsTOP3B was recently demonstrated as the human RNA topoisomerase, required for normal neurodevelopment and proposed to be a potential anti-viral target upon RNA virus infection. Here we elucidate the biochemical mechanisms of human TOP3B. We delineate the roles of divalent metal ions, and of a conserved Lysine residue (K10) in the differential catalysis of DNA and RNA. We also demonstrate that three regulatory factors fine-tune the catalytic performance of TOP3B: the TOP3B C-terminal tail, its protein partner TDRD3, and the sequence of its DNA/RNA substrates.