title: Structural and functional analysis of the ASM p.Ala359Asp mutant that causes acid sphingomyelinase deficiency.
abstract: Niemann-Pick disease (NPD) type A and B are recessive hereditary disorders caused by deficiency in acid sphingomyelinase (ASM). The p.Ala359Asp mutation has been described in several patients but its functional and structural effects in the protein are unknown. In order to characterize this mutation, we modeled the three-dimensional ASM structure using the recent available crystal of the mammalian ASM as a template. We found that the p.Ala359Asp mutation is localized in the hydrophobic core and far from the sphingomyelin binding site. However, energy function calculations using statistical potentials indicate that the mutation causes a decrease in ASM stability. Therefore, we investigated the functional effect of the p.Ala359Asp mutation in ASM expression, secretion, localization and activity in human fibroblasts. We found a 3.8% residual ASM activity compared to the wild-type enzyme, without changes in the other parameters evaluated. These results support the hypothesis that the p.Ala359Asp mutation causes structural alterations in the hydrophobic environment where ASM is located, decreasing its enzymatic activity. A similar effect was observed in other previously described NPDB mutations located outside the active site of the enzyme. This work shows the first full size ASM mutant model describe at date, providing a complete analysis of the structural and functional effects of the p.Ala359Asp mutation over the stability and activity of the enzyme.
authors.affiliation: Departamento de Gastroenterología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile; Center of Genome Regulation (Fondap 15090007), Universidad de Chile, Santiago, Chile. Electronic address: mariana.acuna1@gmail.com.
authors.forename: Mariana
authors.initials: M
authors.lastname: Acuña
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile. Electronic address: vcasfe@ug.uchile.cl.
authors.forename: Víctor
authors.initials: V
authors.lastname: Castro-Fernández
authors.affiliation: Center of Genome Regulation (Fondap 15090007), Universidad de Chile, Santiago, Chile; Laboratorio de Bioinformática y Expresión Génica, INTA, Universidad de Chile, Santiago, Chile; Mathomics, Center for Mathematical Modeling, Universidad de Chile, Santiago, Chile.
authors.forename: Mauricio
authors.initials: M
authors.lastname: Latorre
authors.affiliation: Departamento de Gastroenterología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile.
authors.forename: Juan
authors.initials: J
authors.lastname: Castro
authors.affiliation: Department of Genetics & Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, USA.
authors.forename: Edward H
authors.initials: EH
authors.lastname: Schuchman
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
authors.forename: Victoria
authors.initials: V
authors.lastname: Guixé
authors.affiliation: Center of Genome Regulation (Fondap 15090007), Universidad de Chile, Santiago, Chile; Laboratorio de Bioinformática y Expresión Génica, INTA, Universidad de Chile, Santiago, Chile.
authors.forename: Mauricio
authors.initials: M
authors.lastname: González
authors.affiliation: Departamento de Gastroenterología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile; Center of Genome Regulation (Fondap 15090007), Universidad de Chile, Santiago, Chile. Electronic address: silvana@med.puc.cl.
authors.forename: Silvana
authors.initials: S
authors.lastname: Zanlungo
mesh_terms: D000409:Alanine / Q000737:chemistry; D001224:Aspartic Acid / Q000737:chemistry; D020134:Catalytic Domain; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D046911:Macromolecular Substances; D008856:Microscopy, Fluorescence; D008968:Molecular Conformation; D009154:Mutation; D009542:Niemann-Pick Diseases / Q000235:genetics* / Q000378:metabolism; D000072417:Protein Domains; D013108:Sphingomyelin Phosphodiesterase / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D055672:Static Electricity
chemical_list: D046911:Macromolecular Substances; D001224:Aspartic Acid; C543066:SMPD1 protein, human; D013108:Sphingomyelin Phosphodiesterase; D000409:Alanine
keywords: Acid sphingomylienase; Niemann-pick disease; SMPD1 mutations; p.Ala359Asp