Crystal Structure of the Ubiquitin Binding Domains of Rabex-5 Reveals Two Modes of Interaction with Ubiquitin

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.cell.2006.02.020 Byline: Lorenza Penengo (1), Marina Mapelli (1), Andrea G. Murachelli (1), Stefano Confalonieri (1), Laura Magri (1), Andrea Musacchio (2), Pier Paolo Di Fiore (1)(2)(3), Simona Polo (1)(2), Thomas R. Schneider (1)(2) Abstract: The interaction between ubiquitinated proteins and intracellular proteins harboring ubiquitin binding domains (UBDs) is critical to a multitude of cellular processes. Here, we report that Rabex-5, a guanine nucleotide exchange factor for Rab5, binds to Ub through two independent UBDs. These UBDs determine a number of properties of Rabex-5, including its coupled monoubiquitination and interaction in vivo with ubiquitinated EGFRs. Structural and biochemical characterization of the UBDs of Rabex-5 revealed that one of them (MIU, motif interacting with ubiquitin) binds to Ub with modes superimposable to those of the UIM (ubiquitin-interacting motif):Ub interaction, although in the opposite orientation. The other UBD, RUZ (Rabex-5 ubiquitin binding zinc finger) binds to a surface of Ub centered on Asp58.sub.Ub and distinct from the 'canonical' Ile44.sub.Ub-based surface. The two binding surfaces allow Ub to interact simultaneously with different UBDs, thus opening new perspectives in Ub-mediated signaling. Author Affiliation: (1) IFOM, the FIRC Institute for Molecular Oncology Foundation, Via Adamello 16, 20139 Milan, Italy (2) European Institute of Oncology, Via Ripamonti 435, 20141 Milan, Italy (3) University of Milan, 20122 Milan, Italy Article History: Received 7 December 2005; Revised 6 February 2006; Accepted 14 February 2006 Article Note: (miscellaneous) Published online: February 16, 2006