A ubiquitin-interacting motif from Hrs binds to and occludes the ubiquitin surface necessary for polyubiquitination in monoubiquitinated proteins.
The ubiquitin-interacting motif (UIM) is a short, approximately 20 residue, structural element, which is present in, but not limited to, the proteins involved in endocytotic and proteasomal degradation. UIMs facilitate endocytotic vesicular sorting of the monoubiquitinated proteins and may be important for the targeting of the polyubiquitinated proteins to the proteasome. Using heteronuclear NMR backbone and side-chain chemical shift mapping of the ubiquitin interaction surface, the UIM from the hepatocyte growth factor-regulated tyrosine kinase substrate, Hrs, specifically binds to the ubiquitin hydrophobic surface using UIM's well-conserved central helical LALAL motif. Molecular modeling of the ubiquitin:UIM_Hrs complex suggests that binding occurs through a specific interaction of Leu263 and Leu267 of the UIM_Hrs with two ubiquitin hydrophobic patches located in close proximity to the ubiquitin major polyubiquitination site, Lys48. Intramolecular binding of ubiquitin to a UIM in monoubiquitinated proteins would render Lys48 unavailable for further ubiquitination, thus, explaining the absolute requirement of UIMs for monoubiquitination. Two leucines, Leu265 and Leu269, located on the opposite face of UIM_Hrs can also interact, albeit less favorably than Leu263 and Leu267, with the ubiquitin hydrophobic patches, suggesting a possible mode for polyubiquitin:UIM binding and apparent preference of UIMs for polyubiquitins.
The Rockefeller University, 1230 York Avenue, 10021, New York, NY, USA. shekhta@nysbc.org
Alexander
A
Shekhtman
David
D
Cowburn
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D056827:Endosomal Sorting Complexes Required for Transport; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000378:metabolism; D025801:Ubiquitin / Q000737:chemistry / Q000378:metabolism*
D056827:Endosomal Sorting Complexes Required for Transport; D010455:Peptides; D010750:Phosphoproteins; D011506:Proteins; D025801:Ubiquitin; C096164:hepatocyte growth factor-regulated tyrosine kinase substrate