| Several groups have shown that the inhibition of the Ubiquitin-Proteasome System (UPS) is a critical component of neurodegenerative disease. Recently, it has also been shown that several of these diseases accumulate the frameshifted ubiquitin mutant, UBB+1. This mutant was shown to be inhibitory in vitro upon polyubiquitination, and has been shown to be toxic when expressed in vivo. This inhibition is based on direct competition with the 26S proteasome by preventing the binding of ubiquitinated substrates. In this work, we propose a new mechanism by which polyubiquitinated UBB+1 may inhibit the UPS. We show that polyubiquitinated UBB+1 can inhibit the critical deubiquitinating enzyme, Isopeptidase T. This inhibitor has also given us new insights into the general mechanism of Isopeptidase T by suggesting new roles for Isopeptidase T's binding domains. Additionally, we explore the consequences of UBB+1 expression in mammalian cell culture and its interactions with a fluorescent reporter protein. |
