|M.Sc Student||Glinka Tal|
|Subject||Characterizing the Cellular Role of AIRAPL|
|Department||Department of Medicine||Supervisor||DR. Ariel Stanhill|
|Full Thesis text|
AIRAPL (Arsenite-Inducible Regulatory particle Associated Protein-like) is a protein required for the maintenance of cellular folding capacity in metazoan, as functional impairment of AIRAPL results in acceleration of ageing and protein aggregation. Yet, the cellular roles of AIRAPL in this process are not known. In order to understand the cellular function of this protein, in this thesis we characterized the AIRAPL ubiquitin binding domains and identified a number of proteins that interact with AIRAPL.
We noted that the 160-240 segment of AIRAPL, which contains tandem single and double-sided UIMs (Ubiquitin-Interacting Motifs), is sufficient for ubiquitin binding. The tandem UIMs of AIRAPL are selective towards ubiquitin chains linked via the ubiquitin K48 residue and bind K48 tri-ubiquitin with an affinity of 70nM. Crystal structure of the tandem UIMs indicates two α-helical structures that are separated by a random coil, resulting in a distinct relative orientation of the two UIMs which allows for simultaneous binding to three ubiquitin molecules that are specifically linked through a K48 iso-peptide bond. We also show that AIRAPL is part of an ER localized complex binding specifically to p97 (VCP/Cdc48), Ubxd8, Npl4-Ufd1 and Derlin-1. The interaction between AIRAPL and the different binding partners was shown to be p97 dependant indicating that AIRAPL is a part of a p97-Ufd1-Npl4-Ubxd8-Derlin-1 complex.
As AIRAPL resides in the ER membrane, binds selectively to poly-ubiquitin K48-linked chains and forms a complex with components that have been reported to participate in the endoplasmic reticulum associated degradation (ERAD) pathway, we suggest an involvement of AIRAPL in regulation of ER protein homeostasis.