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46-kDa mannose 6-phosphate-specific receptor: purification, subunit composition, chemical modification
Abstract:
A cation-dependent mannose 6-phosphate-specific receptor has recently been isolated from murine P388D1 macrophages and bovine liver (B. Hoflack & S. Kornfeld, (1985) J. Biol. Chem. 260, 12008-12014). The receptor purified from human liver has a subunit molecular size of 43 kDa, is rich in hydrophobic and charged amino acids and contains threonine at the N-terminus. The receptors from human and rat liver are antigenically related. Both are immunologically distinct from the cation-independent 215-kDa mannose 6-phosphate-specific receptor from human liver. Cross-linking experiments indicate that the cation-dependent receptor exists in solution as a tetramer. Modification of arginine and histidine residues, reduced drastically the binding of the receptor to immobilized ligands. Presence of mannose 6-phosphate during modification of arginine residues protected the binding properties of the receptor, suggesting that arginine is a constituent of the mannose 6-phosphate binding site of the receptor. The significance of the inability of histidine-modified receptors to bind ligands remains to be established.
Insights
Researchers identified a cation-dependent mannose 6-phosphate receptor in human liver. Arginine residues are crucial for its ligand binding, while histidine
Area of Science:
- Biochemistry
- Cell Biology
- Molecular Biology
Background:
- A cation-dependent mannose 6-phosphate (M6P) receptor has been isolated from murine macrophages and bovine liver.
- The human liver M6P receptor subunit has a molecular size of 43 kDa, is rich in hydrophobic and charged amino acids, and has N-terminal threonine.
- Human and rat liver M6P receptors are antigenically related but distinct from the cation-independent 215-kDa M6P receptor.
Purpose of the Study:
- To characterize the cation-dependent mannose 6-phosphate receptor from human liver.
- To investigate the structural and functional properties of the M6P binding site.
- To elucidate the role of specific amino acid residues in receptor-ligand interactions.
Main Methods:
- Purification of the cation-dependent M6P receptor from human liver.
- Chemical modification of arginine and histidine residues.
- Ligand binding assays using immobilized ligands.
- Cross-linking experiments to determine receptor quaternary structure.
Main Results:
- The cation-dependent M6P receptor exists as a tetramer in solution.
- Modification of arginine and histidine residues significantly reduced ligand binding.
- Protection of arginine residues by M6P during modification preserved receptor binding activity.
- Histidine modification abolished ligand binding, but its functional significance requires further investigation.
Conclusions:
- Arginine residues are integral to the mannose 6-phosphate binding site of the cation-dependent M6P receptor.
- The cation-dependent M6P receptor exhibits distinct immunological and structural properties compared to the cation-independent receptor.
- Further studies are needed to understand the role of histidine in the receptor's function.