PDBsum entry 4c9f

Membrane protein

PDB id: 4c9f

Contents

Protein chains

132 a.a.

Ligands

GQ1-GLC ×2

GQ1-GLC-GLC-GLC

SO4 ×10

GQ1 ×3

Metals

_CA ×4

Waters ×164

References listed in PDB file

Key reference

• Title: Structural basis for selective recognition of endogenous and microbial polysaccharides by macrophage receptor sign-R1.
• Authors: N.Silva-Martín, S.G.Bartual, E.Ramírez-Aportela, P.Chacón, C.G.Park, J.A.Hermoso.
• Ref.: Structure, 2014, 22, 1595-1606. [DOI no: 10.1016/j.str.2014.09.001]
• PubMed id: 25450767

Abstract

SIGN-R1 is a principal receptor for microbial polysaccharides uptake and is responsible for C3 fixation via an unusual complement activation pathway on splenic marginal zone macrophages. In these macrophages, SIGN-R1 is also involved in anti-inflammatory activity of intravenous immunoglobulin by direct interaction with sialylated Fcs. The high-resolution crystal structures of SIGN-R1 carbohydrate recognition domain and its complexes with dextran sulfate or sialic acid, and of the sialylated Fc antibody provide insights into SIGN-R1’s selective recognition of a-2,6-sialylated glycoproteins. Unexpectedly, an additional binding site has been found in the SIGNR1 carbohydrate recognition domain, structurally separate from the calcium-dependent carbohydrate-binding site. This secondary binding site could bind repetitive molecular patterns, as observed in microbial polysaccharides, in a calcium-independent manner. These two binding sites may allow SIGNR1 to simultaneously bind both immune glycoproteins and microbial polysaccharide components, accommodating SIGN-R1’s ability to relate the recognition of microbes to the activation of the classical complement pathway.