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EMBO Rep. 2003 Dec;4(12):1169-74. Epub 2003 Nov 7.

The ubiquitin-like protein HUB1 forms SDS-resistant complexes with cellular proteins in the absence of ATP.

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Department of Molecular Cell Biology, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany.


Ubiquitin and ubiquitin-like modifiers (UBLs) form covalent complexes with other proteins by isopeptide formation between their carboxyl (C)-termini and epsilon-amino groups of lysine residues of acceptor proteins. A hallmark of UBLs is a protruding C-terminal tail with a terminal glycine residue, which is required for ATP-dependent conjugation. Recently, the highly conserved protein HUB1 (homologous to ubiquitin 1) has been reported to function as a UBL following C-terminal processing. HUB1 exhibits sequence similarity with ubiquitin but lacks a C-terminal tail bearing a glycine residue. Here we show that HUB1 can form SDS-resistant complexes with cellular proteins, but provide evidence that these adducts are not formed through covalent C-terminal conjugation of HUB1 to substrates. The adducts are still formed when the C-terminus of HUB1 was altered by epitope tagging, amino-acid exchange or deletion, or when cells were depleted of ATP. We propose that HUB1 may act as a novel protein modulator through the formation of tight, possibly noncovalent interactions with target proteins.

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