Identification of the Non-lysosomal Glucosylceramidase as β-Glucosidase 2

Rolf G Boot,Marri Verhoek,Wilma Donker-Koopman,Anneke Strijland,Jan Van Marle,Hermen S Overkleeft,Tom Wennekes,Johannes M F.G Aerts

doi:10.1074/jbc.m610544200

Rolf G Boot, Marri Verhoek + Show 6 more

Open Access

https://doi.org/10.1074/jbc.m610544200

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Abstract

The primary catabolic pathway for glucosylceramide is catalyzed by the lysosomal enzyme glucocerebrosidase that is defective in Gaucher disease patients. A distinct non-lysosomal glucosylceramidase has been described but its identity remained enigmatic for years. We here report that the non-lysosomal glucosylceramidase is identical to the earlier described bile acid beta-glucosidase, being beta-glucosidase 2 (GBA2). Expressed GBA2 is identical to the native non-lysosomal glucosylceramidase in various enzymatic features such as substrate specificity and inhibitor sensitivity. Expression of GBA2 coincides with increased non-lysosomal glucosylceramidase activity, and GBA2-targeted RNA interference reduces endogenous non-lysosomal glucosylceramidase activity in cells. GBA2 is found to be located at or close to the cell surface, and its activity is linked to sphingomyelin generation. Hydrophobic deoxynojirimycins are extremely potent inhibitors for GBA2. In mice pharmacological inhibition of GBA2 activity is associated with impaired spermatogenesis, a phenomenon also very recently reported for GBA2 knock-out mice (Yildiz, Y., Matern, H., Thompson, B., Allegood, J. C., Warren, R. L., Ramirez, D. M., Hammer, R. E., Hamra, F. K., Matern, S., and Russell, D. W. (2006) J. Clin. Invest. 116, 2985-2994). In conclusion, GBA2 plays a role in cellular glucosylceramide metabolism.

Highlights

In higher eukaryotes, glucosylceramide is the precursor of glycosphingolipids, a complex group of ubiquitous membrane lipids, including gangliosides and globosides
GBA2 was excluded as a candidate, because it had been reported that this enzyme is expressed in the liver, is inactive toward glucosylceramide, and is sensitive toward conduritol B epoxide (CBE), all features clearly distinct from those of non-lysosomal glucosylceramidase (NLGase) [4, 24]
Our study indicates that the earlier described non-lysosomal glucosylceramidase, or NLGase, is identical to GBA2, an earlier described bile acid ␤-glucosidase

Summary

Introduction

Glucosylceramide is the precursor of glycosphingolipids, a complex group of ubiquitous membrane lipids, including gangliosides and globosides. Expressed GBA2 is identical to the native non-lysosomal glucosylceramidase in various enzymatic features such as substrate specificity and inhibitor sensitivity. The activity of this enzyme, named non-lysosomal glucosylceramidase (NLGase),2 is not deficient in patients with Gaucher disease and is not located in lysosomes but near the cell surface [4].

Results

Conclusion