title: Bovine brain myelin glycerophosphocholine choline phosphodiesterase is an alkaline lysosphingomyelinase of the eNPP-family, regulated by lysosomal sorting.
abstract: Glycerophosphocholine choline phosphodiesterase (GPC-Cpde) is a glycosylphosphatidylinositol (GPI)-anchored alkaline hydrolase that is expressed in the brain and kidney. In brain the hydrolase is synthesized by the oligodendrocytes and expressed on the myelin membrane. There are two forms of brain GPC-Cpde, a membrane-linked (mGPC-Cpde) and a soluble (sGPC-Cpde). Here we report the characterisation sGPC-Cpde from bovine brain. The amino acid sequence was identical to ectonucleotide pyrophosphatase/phosphodiesterase 6 (eNPP6) precursor, lacking the N-terminal signal peptide region and a C-terminal stretch, suggesting that the hydrolase was solubilised by C-terminal proteolysis, releasing the GPI-anchor. sGPC-Cpde existed as two isoforms, a homodimer joined by a disulfide bridge linking C414 from each monomer, and a monomer resulting from proteolysis N-terminally to this disulfide bond. The only internal disulfide bridge, linking C142 and C154, stabilises the choline-binding pocket. sGPC-Cpde was specific for lysosphingomyelin, displaying 1 to 2 orders of magnitude higher catalytic activity than towards GPC and lysophosphatidylcholine, suggesting that GPC-Cpde may function in the sphingomyelin signaling, rather than in the homeostasis of acylglycerophosphocholine metabolites. The truncated high mannose and bisected hybrid type glycans linked to N118 and N341 of sGPC-Cpde is a hallmark of glycans in lysosomal glycoproteins, subjected to GlcNAc-1-phosphorylation en route through Golgi. Thus, sGPC-Cpde may originate from the lysosomes, suggesting that lysosomal sorting contributes to the level of mGPC-Cpde on the myelin membrane.
authors.affiliation: Institute of Medical Biology, University of Tromso, MH Building, 9037 Tromso, Norway.
authors.forename: Linn
authors.initials: L
authors.lastname: Greiner-Tollersrud
authors.forename: Thomas
authors.initials: T
authors.lastname: Berg
authors.forename: Hilde M F R
authors.initials: HM
authors.lastname: Stensland
authors.forename: Gry
authors.initials: G
authors.lastname: Evjen
authors.forename: Ole K
authors.initials: OK
authors.lastname: Greiner-Tollersrud
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000201:enzymology* / Q000378:metabolism; D001923:Brain Chemistry / Q000235:genetics; D019556:COS Cells; D002417:Cattle; D002522:Chlorocebus aethiops; D006801:Humans; D008247:Lysosomes / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D009186:Myelin Sheath / Q000737:chemistry* / Q000378:metabolism; D010727:Phosphoric Diester Hydrolases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013108:Sphingomyelin Phosphodiesterase / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics
chemical_list: D020033:Protein Isoforms; D010727:Phosphoric Diester Hydrolases; D013108:Sphingomyelin Phosphodiesterase; C061931:glycerophosphocholine cholinephosphodiesterase; C502079:ENPP6 protein, human