title: Structural basis for recognition of phosphodiester-containing lysosomal enzymes by the cation-independent mannose 6-phosphate receptor.
abstract: Mannose 6-phosphate (Man-6-P)-dependent trafficking is vital for normal development. The biogenesis of lysosomes, a major cellular site of protein, carbohydrate, and lipid catabolism, depends on the 300-kDa cation-independent Man-6-P receptor (CI-MPR) that transports newly synthesized acid hydrolases from the Golgi. The CI-MPR recognizes lysosomal enzymes bearing the Man-6-P modification, which arises by the addition of GlcNAc-1-phosphate to mannose residues and subsequent removal of GlcNAc by the uncovering enzyme (UCE). The CI-MPR also recognizes lysosomal enzymes that elude UCE maturation and instead display the Man-P-GlcNAc phosphodiester. This ability of the CI-MPR to target phosphodiester-containing enzymes ensures lysosomal delivery when UCE activity is deficient. The extracellular region of the CI-MPR is comprised of 15 repetitive domains and contains three distinct Man-6-P binding sites located in domains 3, 5, and 9, with only domain 5 exhibiting a marked preference for phosphodiester-containing lysosomal enzymes. To determine how the CI-MPR recognizes phosphodiesters, the structure of domain 5 was determined by NMR spectroscopy. Although domain 5 contains only three of the four disulfide bonds found in the other seven domains whose structures have been determined to date, it adopts the same fold consisting of a flattened beta-barrel. Structure determination of domain 5 bound to N-acetylglucosaminyl 6-phosphomethylmannoside, along with mutagenesis studies, revealed the residues involved in diester recognition, including Y679. These results show the mechanism by which the CI-MPR recognizes Man-P-GlcNAc-containing ligands and provides new avenues to investigate the role of phosphodiester-containing lysosomal enzymes in the biogenesis of lysosomes.
authors.affiliation: Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Olson
authors.forename: Francis C
authors.initials: FC
authors.lastname: Peterson
authors.forename: Alicia
authors.initials: A
authors.lastname: Castonguay
authors.forename: Richard N
authors.initials: RN
authors.lastname: Bohnsack
authors.forename: Mariko
authors.initials: M
authors.lastname: Kudo
authors.forename: Russell R
authors.initials: RR
authors.lastname: Gotschall
authors.forename: William M
authors.initials: WM
authors.lastname: Canfield
authors.forename: Brian F
authors.initials: BF
authors.lastname: Volkman
authors.forename: Nancy M
authors.initials: NM
authors.lastname: Dahms
mesh_terms: D000117:Acetylglucosamine / Q000031:analogs & derivatives; D001665:Binding Sites; D002241:Carbohydrates; D002412:Cations / Q000737:chemistry / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D006867:Hydrolases / Q000378:metabolism; D008024:Ligands; D008247:Lysosomes / Q000201:enzymology* / Q000378:metabolism; D008360:Mannosephosphates; D010727:Phosphoric Diester Hydrolases; D017527:Receptor, IGF Type 2 / Q000737:chemistry* / Q000378:metabolism*; D017451:Receptors, Somatomedin / Q000378:metabolism
chemical_list: D002241:Carbohydrates; D002412:Cations; D008024:Ligands; D008360:Mannosephosphates; D017527:Receptor, IGF Type 2; D017451:Receptors, Somatomedin; C113831:poly-N-acetyl glucosamine; C027693:mannose-6-phosphate; C026146:N-acetylglucosamine-1-phosphate; D006867:Hydrolases; D010727:Phosphoric Diester Hydrolases; C026645:N-acetylglucosamine-1-phosphodiester alpha-N-acetylglucosaminidase; D000117:Acetylglucosamine