Expression and characterization of 14 GLB1 mutant alleles found in GM1-gangliosidosis and Morquio B patients

Raül Santamaria,Amparo Chabás,John W Callahan,Daniel Grinberg,Lluïsa Vilageliu

doi:10.1194/jlr.m700308-jlr200

Abstract

GM1-gangliosidosis and Morquio B disease are lysosomal storage disorders caused by beta-galactosidase deficiency attributable to mutations in the GLB1 gene. On reaching the endosomal-lysosomal compartment, the beta-galactosidase protein associates with the protective protein/cathepsin A (PPCA) and neuraminidase proteins to form the lysosomal multienzyme complex (LMC). The correct interaction of these proteins in the complex is essential for their activity. More than 100 mutations have been described in GM1-gangliosidosis and Morquio B patients, but few have been further characterized. We expressed 12 mutations suspected to be pathogenic, one known polymorphic change (p.S532G), and a variant described as either a pathogenic or a polymorphic change (p.R521C). Ten of them had not been expressed before. The expression analysis confirmed the pathogenicity of the 12 mutations, whereas the relatively high activity of p.S532G is consistent with its definition as a polymorphism. The results for p.R521C suggest that this change is a low-penetrant disease-causing allele. Furthermore, the effect of these beta-galactosidase changes on the LMC was also studied by coimmunoprecipitations and Western blotting. The alteration of neuraminidase and PPCA patterns in several of the Western blotting analyses performed on patient protein extracts indicated that the LMC is affected in at least some GM1-gangliosidosis and Morquio B patients.

Highlights

GM1-gangliosidosis and Morquio B disease are lysosomal storage disorders caused by b-galactosidase deficiency attributable to mutations in the GLB1 gene
The deficiency of lysosomal b-galactosidase caused by mutations in the GLB1 gene is the cause of the rare lysosomal storage disorders GM1-gangliosidosis
The sphingolipid ganglioside GM1 is the main substrate that accumulates in GM1gangliosidosis patients, and the glycosaminoglycan keratan sulfate is the main substrate that accumulates in Morquio B patients

Summary

Introduction

GM1-gangliosidosis and Morquio B disease are lysosomal storage disorders caused by b-galactosidase deficiency attributable to mutations in the GLB1 gene. The alteration of neuraminidase and PPCA patterns in several of the Western blotting analyses performed on patient protein extracts indicated that the LMC is affected in at least some GM1-gangliosidosis and Morquio B patients.— Santamaria, R., A. Expression and characterization of 14 GLB1 mutant alleles found in GM1-gangliosidosis and Morquio B patients. The deficiency of lysosomal b-galactosidase caused by mutations in the GLB1 gene is the cause of the rare lysosomal storage disorders GM1-gangliosidosis EBP is a major component of the nonintegrin cell surface elastin receptor complex, in which EBP binds and protects tropoelastin [3] This complex consists of three units: EBP, neuraminidase, and protective protein/cathepsin A (PPCA). This article is available online at http://www.jlr.org

Methods

Results

Conclusion