Recognition of Dictyostelium discoideum lysosomal enzymes is conferred by the amino-terminal carbohydrate binding site of the insulin-like growth factor II/mannose 6-phosphate receptor.
Biochemistry
; 39(9): 2243-53, 2000 Mar 07.
Article
en En
| MEDLINE
| ID: mdl-10694390
The insulin-like growth factor-II/mannose 6-phosphate receptor (IGF-II/MPR) is a type I glycoprotein that mediates both the intracellular sorting of lysosomal enzymes bearing mannose 6-phosphate (Man-6-P) residues to the lysosome and the bioavailability of IGF-II. The extracytoplasmic region of the IGF-II/MPR contains 15 repeating domains; the two carbohydrate recognition domains (CRDs) have been localized to domains 1-3 and 7-9, and the high-affinity IGF-II binding site maps to domain 11. To characterize the carbohydrate binding properties of the IGF-II/MPR, regions of the receptor encompassing the individual CRDs were produced in a baculovirus expression system. Characterization of the recombinant proteins revealed that the pH optimum for carbohydrate binding is significantly more acidic for the carboxyl-terminal CRD than for the amino-terminal CRD (i.e., pH 6.4-6.5 vs 6.9). Equilibrium binding studies demonstrated that the two CRDs exhibit a similar affinity for Man-6-P. Furthermore, substitution of the conserved arginine residue in domain 3 (R435) or in domain 9 (R1334) with alanine resulted in a similar >1000-fold decrease in the affinity for the lysosomal enzyme, beta-glucuronidase. In contrast, the two CRDs differ dramatically in their ability to recognize the distinctive modifications (i.e., mannose 6-sulfate and Man-6-P methyl ester) found on Dictyostelium discoideum lysosomal enzymes: the amino-terminal CRD binds mannose 6-sulfate and Man-6-P methyl ester with a 14-55-fold higher affinity than the carboxyl-terminal CRD. Taken together, these results demonstrate that the IGF-II/MPR contains two functionally distinct CRDs.
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Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Receptor IGF Tipo 2
/
Dictyostelium
/
Lisosomas
/
Manosafosfatos
Límite:
Animals
/
Humans
Idioma:
En
Revista:
Biochemistry
Año:
2000
Tipo del documento:
Article
País de afiliación:
Estados Unidos
Pais de publicación:
Estados Unidos