Journal Article

Characterization of the sialidase molecular defects in sialidosis patients suggests the structural organization of the lysosomal multienzyme complex

Kiven E. Lukong, Marc-André Elsliger, Yuan Chang, Catherine Richard, George Thomas, William Carey, Anna Tylki-Szymanska, Barbara Czartoryska, Tina Buchholz, German Rodríguez Criado, Silvia Palmeri and Alexey V. Pshezhetsky

in Human Molecular Genetics

Volume 9, issue 7, pages 1075-1085
Published in print April 2000 | ISSN: 0964-6906
Published online April 2000 | e-ISSN: 1460-2083 | DOI: http://dx.doi.org/10.1093/hmg/9.7.1075
Characterization of the sialidase molecular defects in sialidosis patients suggests the structural organization of the lysosomal multienzyme complex

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Sialidosis is an autosomal recessive disease caused by the genetic deficiency of lysosomal sialidase, which catalyzes the hydrolysis of sialoglycocon­jugates. The disease is associated with progressive impaired vision, macular cherry-red spots and myoclonus (sialidosis type I) or with skeletal dysplasia, Hurler-like phenotype, dysostosis multiplex, mental retardation and hepatosplenomegaly (sialidosis type II). We have analyzed the genomic DNA from nine sialidosis patients of multiple ethnic origin in order to find mutations responsible for the enzyme deficiency. The activity of the identified variants was studied by transgenic expression. One patient had a frameshift mutation (G623delG deletion), which introduced a stop codon, truncating 113 amino acids. All others had missense mutations: G679G→A (Gly227Arg), C893C→T (Ala298Val), G203G→T (Gly68Val), A544A→G (Ser182Gly) C808C→T (Leu270Phe) and G982G→A (Gly328Ser). We have modeled the three-dimensional structure of sialidase based on the atomic coordinates of the homologous bacterial sialidases, located the positions of mutations and estimated their potential effect. This analysis showed that five mutations are clustered in one region on the surface of the sialidase molecule. These mutations dramatically reduce the enzyme activity and cause a rapid intralysosomal degradation of the expressed protein. We hypothesize that this region may be involved in the interface of sialidase binding with lysosomal cathepsin A and/or β-galactosidase in their high-molecular-weight complex required for the expression of sialidase activity in the lysosome.

Journal Article.  7966 words.  Illustrated.

Subjects: Genetics and Genomics

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