title: Lysosomal membranes from beige mice contain higher than normal levels of endoplasmic reticulum proteins.
abstract: Chediak-Higashi syndrome is characterized by dysfunctional giant organelles of common origin, that is, lysosomes, melanosomes, and platelet dense bodies. Its defective gene LYST encodes a large molecular weight protein whose function is unknown. The Beige mouse also defective in Lyst is a good model of the human disease. Purified lysosomes from Beige and normal black mouse livers were used to carry out a proteomics study. Two-dimensional gel electrophoretic separation of soluble lysosomal proteins of Beige and normal mice revealed no major differences. The cleavable isotope-coded affinity tag (cICAT) technique was used to compare the composition of Beige and normal lysosomal membrane proteins. While the levels of common proteins, that is, Lamp1, Lamp2, and Niemann-Pick type C1, were decreased in Beige mice, there was an increase in the levels of endoplasmic reticulum (ER) resident proteins, for example, cytochrome P450, NADPH-cytochrome P450 oxidoreductase, and flavin-containing monooxygenase. Confocal microscopy confirmed that another ER protein, calnexin, colocalizes with Lamp1 on membranes of giant lysosomes from fibroblasts of Chediak-Higashi syndrome patient. Our results suggest that LYST may play a role in either preventing inappropriate incorporation of proteins into the lysosomal membrane or in membrane recycling/maturation.
authors.affiliation: Research Institute, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada.
authors.forename: Huiwen
authors.initials: H
authors.lastname: Zhang
authors.forename: Xiaolian
authors.initials: X
authors.lastname: Fan
authors.forename: Richard D
authors.initials: RD
authors.lastname: Bagshaw
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Don J
authors.initials: DJ
authors.lastname: Mahuran
authors.forename: John W
authors.initials: JW
authors.lastname: Callahan
mesh_terms: D000818:Animals; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D007425:Intracellular Membranes / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism*; D013058:Mass Spectrometry; D051379:Mice; D008810:Mice, Inbred C57BL; D008854:Microscopy, Electron; D046529:Microscopy, Electron, Transmission; D040901:Proteomics / Q000379:methods*; D013347:Subcellular Fractions / Q000378:metabolism