The ubiquitin-like protein HUB1 forms SDS-resistant complexes with cellular proteins in the absence of ATP.
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.
Lüders
Jens
J
Department of Molecular Cell Biology, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany.
Pyrowolakis
George
G
Jentsch
Stefan
S
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D008025:Ligases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008239:Lysine / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D025842:SUMO-1 Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D012967:Sodium Dodecyl Sulfate; D014452:Ubiquitins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D010446:Peptide Fragments; D025842:SUMO-1 Protein; D029701:Saccharomyces cerevisiae Proteins; D014452:Ubiquitins; D012967:Sodium Dodecyl Sulfate; D000255:Adenosine Triphosphate; D008025:Ligases; C452202:HUB1 protein, S cerevisiae; D008239:Lysine