A cysteine-rich domain of the “mannose” receptor mediates GalNAc-4-SO ₄ binding

Abstract

A critical element of lutropin bioactivity in vivo is its rapid removal from the blood by a receptor, located in hepatic endothelial cells, that recognizes the terminal sulfated carbohydrate structure SO 4 -4-GalNAc␤1,4Glc-NAc␤1,2Man␣ (S4GGnM). We have previously shown that the macrophage mannose (Man)-receptor cDNA directs the synthesis of a protein that binds oligosaccharides with either terminal S4GGnM or terminal Man, at independent sites. We now show that the cysteine-rich (Cys-Rich) domain at the N terminus of the Man͞S4GGnM receptor accounts for binding of oligosaccharides with terminal GalNAc-4-SO 4 , whereas calcium-dependent carbohydrate recognition domains (CRDs) account for binding of ligands containing terminal Man. The Cys-Rich domain is thus a previously unrecognized carbohydrate binding motif. Cys-Rich domains have been described on the three other members of the endocytic C-type lectin family of receptors. The structural relationship of these receptors to the Man͞S4GGnM receptor raises the possibility that their Cys-Rich domains also bind carbohydrate moieties and contribute to their function.Glycoproteins such as lutropin (LH) and thyrotropin that bear multiple Asn-linked oligosaccharides terminating with the sequence SO 4 -4-GalNAc␤1,4GlcNAc␤1,2Man␣ (S4GGnM) are rapidly removed from the circulation by an S4GGnM-specific receptor found at the surface of hepatic endothelial cells (1, 2). Precise control of the circulatory half-life of LH is thought to be critical for attaining maximal stimulation of the LH receptor located in the ovary during the preovulatory surge in LH levels. We recently reported (3) that the S4GGnM receptor (S4GGnM-R) isolated from rat liver is closely related to the macrophage mannose receptor (Man-R) isolated from rat lung. However, the liver S4GGnM-R and lung Man-R display marked differences in ligand specificity and binding properties.

Multiple interactions between pituitary hormones and the mannose receptor

“…These results are consistent with a specific SO % -4GalNAc-binding site being localized to the cysteine-rich domain [9]. SO % -6Gal was 5-15-fold less effective as an inhibitor of hormone binding to MMR-S than SO % -4GalNAc, indicating specificity for the sugar portion of the ligand and not just the sulphate group.…”

“…TSH and LH also showed saturable binding [8]. These results are not inconsistent with the SO % -4GalNAc binding site being localized to the cysteine-rich domain of the mannose receptor [9] but they indicate that the CRDs of the receptor can also interact with pituitary hormones.…”

“…This result was unexpected because the binding of pituitary hormones was thought to be largely due to the recognition of terminal SO % -4GalNAc residues and a binding site for SO % -4GalNAc has been localized to the cysteine-rich domain of the mannose receptor [9]. However, the binding of hormones to the truncated form of the receptor is not inhibited by SO % -4GalNAc, indicating that there is no specific interaction of the receptor CRDs with terminal SO % -4GalNAc residues of the hormones.…”

“…ing of BSA conjugated to the trisaccharide SO % -4GalNAcβ1,4GlcNAcβ1,2Manα, suggest that the mannosebinding and SO % -4GalNAc-binding sites of the mannose receptor are distinct, with the SO % -4GalNAc-binding site being localized to the N-terminal cysteine-rich domain [9]. No previous ligandbinding activity has been associated with the cysteine-rich domain, which is unique to the mannose receptor and three other receptors in the mannose receptor family, and shows no sequence similarity to other carbohydrate-binding proteins [10].…”

Glycosylation of surface Ig creates a functional bridge between human follicular lymphoma and microenvironmental lectins

“…2 A and B). Binding of the Control-MR, particularly evident for FL21, seemed to be at least partly Ca 2+ independent and presumably represents binding by the cysteine-rich domain, which has specificity for sulfated glycans (20).…”