PMID: 21172656

Authors:

Satoh T, Chen Y, Hu D, Hanashima S, Yamamoto K, Yamaguchi Y

Title:

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

Journal:

Mol Cell. 2010 Dec 22;40(6):905-16.

Abstract:

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 alpha1,2-linked mannose on C-arm of high-mannose-type glycan and binding of processed alpha1,6-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 alpha3,alpha6-mannopentaose. The OS-9(MRH) has a flattened beta-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 Manalpha1,6Manalpha1,6Man residues on the processed C-arm through the continuous double tryptophan (WW) motif.