β-Glucosidase 2 (GBA2) Activity and Imino Sugar Pharmacology

• Published in: The Journal of biological chemistry 2013-09, Vol.288 (36), p.26052-26066
• Main Authors: Ridley, Christina M., Thur, Karen E., Shanahan, Jessica, Thillaiappan, Nagendra Babu, Shen, Ann, Uhl, Karly, Walden, Charlotte M., Rahim, Ahad A., Waddington, Simon N., Platt, Frances M., van der Spoel, Aarnoud C.
• Format: Article
• Language: English
• Subjects: 1-Deoxynojirimycin - analogs & derivatives; 1-Deoxynojirimycin - pharmacokinetics; 1-Deoxynojirimycin - pharmacology; Animals; beta-Glucosidase - antagonists & inhibitors; beta-Glucosidase - metabolism; Cell Line, Tumor; Cerebellar Ataxia - drug therapy; Cerebellar Ataxia - enzymology; Chlorocebus aethiops; Conduritol B Epoxide; COS Cells; Enzyme Inhibitors; Enzyme Inhibitors - pharmacokinetics; Enzyme Inhibitors - pharmacology; Glucosylceramidase; Glucosylceramide; Glycolipids; Glycoside Hydrolases; Humans; Hydrogen-Ion Concentration; Inositol - analogs & derivatives; Inositol - pharmacokinetics; Inositol - pharmacology; Lipids; Mechanism-based Enzyme Inhibitor; Membrane Lipids; Mice; Miglustat; Nonlysosomal Glucosylceramidase; Spastic Paraplegia, Hereditary - drug therapy; Spastic Paraplegia, Hereditary - enzymology; Sphingolipid
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M113.463562

β-Glucosidase 2 (GBA2) is an enzyme that cleaves the membrane lipid glucosylceramide into glucose and ceramide. The GBA2 gene is mutated in genetic neurological diseases (hereditary spastic paraplegia and cerebellar ataxia). Pharmacologically, GBA2 is reversibly inhibited by alkylated imino sugars that are in clinical use or are being developed for this purpose. We have addressed the ambiguity surrounding one of the defining characteristics of GBA2, which is its sensitivity to inhibition by conduritol B epoxide (CBE). We found that CBE inhibited GBA2, in vitro and in live cells, in a time-dependent fashion, which is typical for mechanism-based enzyme inactivators. Compared with the well characterized impact of CBE on the lysosomal glucosylceramide-degrading enzyme (glucocerebrosidase, GBA), CBE inactivated GBA2 less efficiently, due to a lower affinity for this enzyme (higher KI) and a lower rate of enzyme inactivation (kinact). In contrast to CBE, N-butyldeoxygalactonojirimycin exclusively inhibited GBA2. Accordingly, we propose to redefine GBA2 activity as the β-glucosidase that is sensitive to inhibition by N-butyldeoxygalactonojirimycin. Revised as such, GBA2 activity 1) was optimal at pH 5.5–6.0; 2) accounted for a much higher proportion of detergent-independent membrane-associated β-glucosidase activity; 3) was more variable among mouse tissues and neuroblastoma and monocyte cell lines; and 4) was more sensitive to inhibition by N-butyldeoxynojirimycin (miglustat, Zavesca®), in comparison with earlier studies. Our evaluation of GBA2 makes it possible to assess its activity more accurately, which will be helpful in analyzing its physiological roles and involvement in disease and in the pharmacological profiling of monosaccharide mimetics. Background: GBA2 and GBA are both β-glucosidases that degrade glucosylceramide. Results: Conduritol B epoxide inactivates both GBA and GBA2, whereas the imino sugar NB-DGJ selectively inhibits GBA2. Conclusion:NB-DGJ is a suitable reagent to distinguish GBA2 from GBA. Significance: This study redefines GBA2 activity, which is relevant for clinical GBA2 measurements and imino sugar pharmacology.