title: Molecular imaging of membrane interfaces reveals mode of beta-glucosidase activation by saposin C.
abstract: Acid beta-glucosidase (GCase) is a soluble lysosomal enzyme responsible for the hydrolysis of glucose from glucosylceramide and requires activation by the small nonenzymatic protein saposin C (sapC) to gain access to the membrane-embedded glycosphingolipid substrate. We have used in situ atomic force microscopy (AFM) with simultaneous confocal and epifluorescence microscopies to investigate the interactions of GCase and sapC with lipid bilayers. GCase binds to sites on membranes transformed by sapC, and enzyme activity occurs at loci containing both GCase and sapC. Using FRET, we establish the presence of GCase/sapC and GCase/product contacts in the bilayer. These data support a mechanism in which sapC locally alters regions of bilayer for subsequent attack by the enzyme in stably bound protein complexes.
authors.affiliation: Division of Cancer Genomics and Proteomics, Ontario Cancer Institute, 101 College Street, Toronto, ON, Canada M5G 1L7.
authors.forename: Jean-René
authors.initials: JR
authors.lastname: Alattia
authors.forename: James E
authors.initials: JE
authors.lastname: Shaw
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Yip
authors.forename: Gilbert G
authors.initials: GG
authors.lastname: Privé
mesh_terms: D004789:Enzyme Activation / Q000187:drug effects; D008051:Lipid Bilayers / Q000378:metabolism*; D018625:Microscopy, Atomic Force; D011485:Protein Binding; D049231:Saposins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D001617:beta-Glucosidase / Q000378:metabolism*
chemical_list: D008051:Lipid Bilayers; D049231:Saposins; D001617:beta-Glucosidase