Cells 2014, 3, 1027-1088; doi:10.3390/cells3041027 OPEN ACCESS cells ISSN 2073-4409 www.mdpi.com/journal/cells Review Versatile Roles of K63-Linked Ubiquitin Chains in Trafficking Zoi Erpapazoglou 1,2, Olivier Walker 3 and Rosine Haguenauer-Tsapis 1,* 1 Institut Jacques Monod-CNRS, UMR 7592, Université-Paris Diderot, Sorbonne Paris Cité, F-75205 Paris, France; E-Mail:
[email protected] 2 Current address: Brain and Spine Institute, CNRS UMR 7225, Inserm, U 1127, UPMC-P6 UMR S 1127, 75013 Paris, France 3 Institut des Sciences Analytiques, UMR5280, Université de Lyon/Université Lyon 1, 69100 Villeurbanne, France; E-Mail:
[email protected] * Author to whom correspondence should be addressed; E-Mail:
[email protected]. External Editor: Hanjo Hellmann Received: 14 July 2014; in revised form: 14 October 2014 / Accepted: 21 October 2014 / Published: 12 November 2014 Abstract: Modification by Lys63-linked ubiquitin (UbK63) chains is the second most abundant form of ubiquitylation. In addition to their role in DNA repair or kinase activation, UbK63 chains interfere with multiple steps of intracellular trafficking. UbK63 chains decorate many plasma membrane proteins, providing a signal that is often, but not always, required for their internalization. In yeast, plants, worms and mammals, this same modification appears to be critical for efficient sorting to multivesicular bodies and subsequent lysosomal degradation. UbK63 chains are also one of the modifications involved in various forms of autophagy (mitophagy, xenophagy, or aggrephagy). Here, in the context of trafficking, we report recent structural studies investigating UbK63 chains assembly by various E2/E3 pairs, disassembly by deubiquitylases, and specifically recognition as sorting signals by receptors carrying Ub-binding domains, often acting in tandem.