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Proc Natl Acad Sci U S A. 2007 Oct 30;104(44):17394-9. Epub 2007 Oct 22.

Molecular imaging of membrane interfaces reveals mode of beta-glucosidase activation by saposin C.

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1
Division of Cancer Genomics and Proteomics, Ontario Cancer Institute, 101 College Street, Toronto, ON, Canada M5G 1L7.

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.

PMID:
17954913
PMCID:
PMC2077267
DOI:
10.1073/pnas.0704998104
[Indexed for MEDLINE]
Free PMC Article
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