Bellinzona – June 13 2024 – A new study published by the Cejka laboratory and collaborators in “Molecular Cell” provides molecular insight into the activation of Mre11-Rad50- endonuclease activity by Sae2/CtIP.
In Saccharomyces cerevisiae (S. cerevisiae), Mre11-Rad50-Xrs2 (MRX)-Sae2 nuclease activity is required for the resection of DNA breaks with secondary structures or protein blocks, while in humans, the MRE11-RAD50-NBS1 (MRN) homolog with CtIP is needed to initiate DNA end resection of all breaks. Phosphorylated Sae2/CtIP stimulates the endonuclease activity of MRX/N. Structural insights into the activation of the Mre11 nuclease are available only for organisms lacking Sae2/CtIP, so little is known about how Sae2/CtIP activates the nuclease ensemble. Using a combination of AlphaFold2 structural modeling and biochemical and genetic assays the authors uncover the mechanism of Mre11 activation by Sae2. They show how phosphorylated Sae2 stabilizes the cutting state of the Mre11 nuclease. Several designs of compensatory mutations establish how Sae2 activates MRX in vitro and in vivo, supporting the structural model. Finally, the study uncovers how human CtIP, despite considerable sequence divergence, employs a similar mechanism to activate MRN and highlight structural rearrangements that may have occurred during evolution from a common ancestor of Sae2 and CtIP.
Elda Cannavo, from the Cejka laboratory (Institute for Research in Biomedicine in Bellinzona, affiliated with the Faculty of Biochemical Sciences of the Università della Svizzera italiana) is one of the co-first authors of the study and Petr Cejka is the lead contact together with Valérie Borde (Institut Curie, Paris, France ) and Raphaël Guerois (Institute for integrative Biology of the Cell, Paris, France).
