Structural basis for disparate sugar-binding specificities in the homologous cargo receptors ERGIC-53 and VIP36

PLoS One. 2014 Feb 3;9(2):e87963. doi: 10.1371/journal.pone.0087963. eCollection 2014.

Abstract

ERGIC-53 and VIP36 are categorized as leguminous type (L-type) lectins, and they function as cargo receptors for trafficking certain N-linked glycoproteins in the secretory pathway in animal cells. They share structural similarities in their carbohydrate recognition domains (CRDs) but exhibit distinct sugar-binding specificities and affinities. VIP36 specifically interacts with the α1,2-linked D1 mannosyl arm without terminal glucosylation, while ERGIC-53 shows a broader specificity and lower binding affinity to the high-mannose-type oligosaccharides, irrespective of the presence or absence of the non-reducing terminal glucose residue at the D1 arm. In this study, we determined the crystal structure of ERGIC-53-CRD in complex with their binding partner, MCFD2 and the α1,2 mannotriose which corresponds to the trisaccharide of the D1 arm of high-mannose-type glycans. ERGIC-53 can interact with the D1 trimannosyl arm in two alternative modes, one of which is similar but distinct from that previously observed for VIP36. ERGIC-53 has a shallower sugar-binding pocket than VIP36 because of the single amino acid substitution, Asp-to-Gly. This enables ERGIC-53 to accommodate the non-reducing terminal glucose of the D1 arm in its CRD. In the other interaction mode, the 3-OH group of the terminal mannose was situated outward with respect to the sugar binding pocket, also enabling the Glcα1-3 linkage formation without steric hindrance. Our findings thus provide a structural basis for the broad sugar-binding specificity of the ERGIC-53/MCFD2 cargo receptor complex.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Crystallography, X-Ray
  • Humans
  • Mannose-Binding Lectins / chemistry*
  • Mannose-Binding Lectins / metabolism
  • Membrane Proteins / chemistry*
  • Membrane Proteins / metabolism
  • Membrane Transport Proteins / chemistry*
  • Membrane Transport Proteins / metabolism
  • Models, Molecular
  • Protein Binding
  • Protein Conformation
  • Substrate Specificity
  • Trisaccharides / chemistry*
  • Trisaccharides / metabolism
  • Vesicular Transport Proteins / chemistry*
  • Vesicular Transport Proteins / metabolism

Substances

  • LMAN1 protein, human
  • LMAN2 protein, human
  • MCFD2 protein, human
  • Mannose-Binding Lectins
  • Membrane Proteins
  • Membrane Transport Proteins
  • Trisaccharides
  • Vesicular Transport Proteins
  • mannotriose

Grants and funding

This work was supported in part by JSPS KAKENHI (Grant Numbers 24770102, 25121730 to T.S., and 25102008, 24249002 to K.K.) and by the Okazaki ORION project. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.