Truncated mutants of beta-glucosidase 2 (GBA2) are localized in the mitochondrial matrix and cause mitochondrial fragmentation

The enzyme β-glucosidase 2 (GBA2) is clinically relevant because it is targeted by the drug miglustat (Zavesca(®)) and because it is involved in inherited diseases. Mutations in the GBA2 gene are associated with two neurological diseases on the ataxia-spasticity spectrum, hereditary spastic paraplegia 46 (SPG46) and Marinesco-Sjögren-like syndrome (MSS). To establish how GBA2 mutations give rise to neurological pathology, we have begun to investigate mutant forms of GBA2 encoded by disease-associated GBA2 alleles. Previously, we found that five GBA2 missense mutants and five C-terminally truncated mutants lacked enzyme activity. Here we have examined the cellular locations of wild-type (WT) and mutant forms of GBA2 by confocal and electron microscopy, using transfected cells. Similar to GBA2-WT, the D594H and M510Vfs*17 GBA2 mutants were located at the plasma membrane, whereas the C-terminally truncated mutants terminating after amino acids 233 and 339 (GBA2-233 and -339) were present in the mitochondrial matrix, induced mitochondrial fragmentation and loss of mitochondrial transmembrane potential. Deletional mutagenesis indicated that residues 161–200 are critical for the mitochondrial fragmentation of GBA2-233 and -339. Considering that the mitochondrial fragmentation induced by GBA2-233 and -339 is consistently accompanied by their localization to the mitochondrial matrix, our deletional analysis raises the possibility that that GBA2 residues 161–200 harbor an internal targeting sequence for transport to the mitochondrial matrix. Altogether, our work provides new insights into the behaviour of GBA2-WT and disease-associated forms of GBA2.