Identification of residues essential for carbohydrate recognition by the insulin-like growth factor II/mannose 6-phosphate receptor.
Two distinct mannose 6-phosphate (Man-6-P) receptors (MPRs), the cation-dependent MPR (CD-MPR) and the insulin-like growth factor II/MPR (IGF-II/MPR), recognize a diverse population of Man-6-P-containing ligands. The IGF-II/MPR is a type I transmembrane glycoprotein with a large extracytoplasmic region composed of 15 repeating domains that display sequence identity to each other and to the single extracytoplasmic domain of the CD-MPR. A structure-based sequence alignment of the two distinct Man-6-P-binding sites of the IGF-II/MPR with the CD-MPR implicates several residues of IGF-II/MPR domains 3 and 9 as essential for Man-6-P binding. To test this hypothesis single amino acid substitutions were made in constructs encoding either the N- or the C-terminal Man-6-P-binding sites of the bovine IGF-II/MPR. The mutant IGF-II/MPRs secreted from COS-1 cells were analyzed by pentamannosyl phosphate-agarose affinity chromatography, identifying four residues (Gln-392, Ser-431, Glu-460, and Tyr-465) in domain 3 and four residues (Gln-1292, His-1329, Glu-1354, and Tyr-1360) in domain 9 as essential for Man-6-P recognition. Binding affinity studies using the lysosomal enzyme, beta-glucuronidase, confirmed these results. Together these analyses provide strong evidence that the two Man-6-P-binding sites of the IGF-II/MPR are structurally similar to each other and to the CD-MPR and utilize a similar carbohydrate recognition mechanism.
Hancock
Michael K
MK
Department of Biochemistry, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA.
Haskins
Darin J
DJ
Sun
Guangjie
G
Dahms
Nancy M
NM
D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D017931:DNA Primers; D007335:Insulin-Like Growth Factor II / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017386:Sequence Homology, Amino Acid
D017931:DNA Primers; D007335:Insulin-Like Growth Factor II