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carboxyl-terminal domain of ubiquitin-specific protease 25 (USP25) and 28 (USP28), and similar domains This family contains the C-terminal domain of two deubiquitinases (DUBs), ubiquitin-specific proteases USP25 and USP28, which share high similarity but vary in their cellular functions. USP25 is a regulator of the innate immune system and may play a role in tumorigenesis, while USP28 is known for its tumor-promoting role. These two closely related DUBs contain an N-terminal domain harboring a Ub-associated domain (UBA) and two Ub-interacting motifs (UIMs), a central catalytic USP domain, and a C-terminal region of unknown function and variable size due to alternative splicing. In general, USP catalytic domains are around 350 amino acids in length; however, in USP25 and 28, the catalytic domains span around 550 amino acids due to a large, conserved insertion at a common insertion point called USP25/28 catalytic domain inserted domain (UCID). This alignment model represents the C-terminal region that has been implicated in substrate binding for both USP25 and USP28 and harbors the splicing site for isoform-specific sequences.
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