Structural Basis for Oligosaccharide Recognition of Misfolded Glycoproteins by OS-9 in ER-Associated Degradation

• Published in: Molecular cell Vol. 40; no. 6; pp. 905 - 916
• Main Authors: Satoh, Tadashi, Chen, Yang, Hu, Dan, Hanashima, Shinya, Yamamoto, Kazuo, Yamaguchi, Yoshiki
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 22.12.2010
• Subjects: Carbohydrate Conformation; Crystallography, X-Ray; Endoplasmic Reticulum - metabolism; Glycoproteins - chemistry; Glycoproteins - metabolism; Humans; Lectins - chemistry; Lectins - metabolism; Models, Molecular; Neoplasm Proteins - metabolism; Nuclear Magnetic Resonance, Biomolecular; Oligosaccharides - chemistry; Oligosaccharides - metabolism; Protein Folding; Receptor, IGF Type 2 - chemistry; Receptor, IGF Type 2 - metabolism
• ISSN: 1097-2765; 1097-4164
• DOI: 10.1016/j.molcel.2010.11.017

Misfolded glycoproteins are translocated from endoplasmic reticulum (ER) into the cytosol for proteasome-mediated degradation. A mannose-6-phosphate receptor homology (MRH) domain is commonly identified in a variety of proteins and, in the case of OS-9 and XTP3-B, is involved in glycoprotein ER-associated degradation (ERAD). Trimming of outermost α1,2-linked mannose on C-arm of high-mannose-type glycan and binding of processed α1,6-linked mannosyl residues by the MRH domain are critical steps in guiding misfolded glycoproteins to enter ERAD. Here we report the crystal structure of a human OS-9 MRH domain (OS-9 MRH) complexed with α3,α6-mannopentaose. The OS-9 MRH has a flattened β-barrel structure with a characteristic P-type lectin fold and possesses distinctive double tryptophan residues in the oligosaccharide-binding site. Our crystallographic result in conjunction with nuclear magnetic resonance (NMR) spectroscopic and biochemical results provides structural insights into the mechanism whereby OS-9 specifically recognizes Manα1,6Manα1,6Man residues on the processed C-arm through the continuous double tryptophan (WW) motif. [Display omitted] ► OS-9 MRH domain has a flattened β-barrel structure with P-type lectin fold ► OS-9 recognizes α1,6-linked Man 3 on C-arm of N-glycans through WW motif ► Trimming of outermost α1,2-linked Man on C-arm is essential for the binding to OS-9 ► OS-9 binds glycoprotein ERAD substrate through the WW motif