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Publication Abstract from PubMed

SCF(Fbs1) is a ubiquitin ligase that functions in the endoplasmic reticulum (ER)-associated degradation pathway. Fbs1/Fbx2, a member of the F-box proteins, recognizes high-mannose oligosaccharides. Efficient binding to an N-glycan requires di-N-acetylchitobiose (chitobiose). Here we report the crystal structures of the sugar-binding domain (SBD) of Fbs1 alone and in complex with chitobiose. The SBD is composed of a ten-stranded antiparallel beta-sandwich. The structure of the SBD-chitobiose complex includes hydrogen bonds between Fbs1 and chitobiose and insertion of the methyl group of chitobiose into a small hydrophobic pocket of Fbs1. Moreover, NMR spectroscopy has demonstrated that the amino acid residues adjoining the chitobiose-binding site interact with the outer branches of the carbohydrate moiety. Considering that the innermost chitobiose moieties in N-glycans are usually involved in intramolecular interactions with the polypeptide moieties, we propose that Fbs1 interacts with the chitobiose in unfolded N-glycoprotein, pointing the protein moiety toward E2 for ubiquitination.

Structural basis of sugar-recognizing ubiquitin ligase.,Mizushima T, Hirao T, Yoshida Y, Lee SJ, Chiba T, Iwai K, Yamaguchi Y, Kato K, Tsukihara T, Tanaka K Nat Struct Mol Biol. 2004 Apr;11(4):365-70. Epub 2004 Feb 29. PMID:14990996^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.