Structural bases of Wolman disease and cholesteryl ester storage disease☆
Highlights
► We built a structural model of human lysosomal acid lipase. ► The residues responsible for WD/CESD tend to be more interior than the others. ► Large conformational changes tend to cause the severe clinical phenotype (WD). ► Conformational changes of the functionally important residues tend to cause WD. ► Small conformational changes tend to cause the mild clinical phenotype.
Introduction
Lysosomal acid lipase (LAL, EC 3.1.1.13) is essential for the hydrolysis of triglycerides and cholesteryl esters in lysosomes. A deficiency of LAL activity causes the accumulation of triglycerides and cholesteryl esters in lysosomes, leading to two autosomal recessive genetic disorders, Wolman disease (WD; McKusick 278000) and cholesteryl ester storage disease (CESD; McKusick 21500) [1]. Patients with WD, an early-onset severe phenotype, usually succumb to hepatic and adrenal failure within the first year of life. In contrast, patients with CESD exhibit a late-onset moderate phenotype.
Both WD and CESD are caused by mutations in the LAL gene (LIPA) on chromosome 10q23.2–q23.3, and they are basically distinguished by the level of residual activity of the mutant LAL [2]. In WD, the LAL activity is almost completely absent. In contrast, the mutant LAL associated with CESD exhibits residual LAL activity [2].
So far, various kinds of gene mutations causing WD and CESD have been identified [1], [3], [4], [5], [6], [7], [8], [9]. In general, nonsense mutations, deletions, and insertions in LIPA are associated with WD, although there are some exceptions (e.g., p.G245X). On the other hand, as to missense mutations, the phenotypes are heterogeneous; some of them cause WD, and the others CESD. Previous investigation revealed that patients heterozygous for a WD mutation (E8SJM + 1) and a CESD one (p.G66V, p.P181L, p.L273S or p.H274Y) exhibited the CESD phenotype [6], suggesting that CESD mutations dominantly influence the phenotype.
Roussel et al. determined the crystal structure of human gastric lipase and built the homology model of LAL with human gastric lipase as a template. As LAL displays high sequence homology with gastric lipase without any insertion or deletion (amino acid identity 59%), the reliability of their homology model of LAL is thought to be high. Based on the homology model, they gave possible explanations for some partial deletions and missense mutations [10]. However, the details of the influence of structural changes in LAL on the pathogeneses of WD and CESD remain obscure.
In this study, we performed structural analysis of LAL from a different viewpoint to obtain further insight into the bases of WD and CESD. First, we constructed a three-dimensional model of LAL, and then determined the solvent-accessible surface area (ASA) values. Then, we built structural models of the mutant LAL proteins and examined their structural changes by calculating the numbers of atoms influenced by the amino acid replacements, and determined the root-mean-square deviation (RMSD) values. Furthermore, we examined the distributions and degrees of structural changes caused by the amino acid substitutions by coloring the influenced atoms based on the distances between the wild-type and mutant ones.
Section snippets
Mutations
The missense mutations analyzed in this study are summarized in Table 1. The clinical phenotypes and residual activity were written according to the original reports.
Structural modeling of mutant LAL proteins
Structural models of mutant LAL proteins were constructed with molecular modeling software Modeller [11] and TINKER [12], [13], [14], [15], [16] using the structure of human gastric lipase (protein data bank code: 1HLG [10]) as a template. All mutant models were energy minimized until the root-mean-square gradient value was lower
Localization of the amino acid residues of which substitutions are associated with WD/CESD in the LAL molecule
We built a three-dimensional model of human LAL using human gastric lipase as a template (Figs. 1a and b). Then, we determined the locations of amino acid substitutions that are associated with WD/CESD in the human LAL molecule (Fig. 1b). The ASA values of the amino acids, of which substitutions are responsible for WD/CESD, are shown in Table 1. The average value for the residues associated with WD/CESD is 11.9 Å2, that for the others being 40.7 Å2. The results of the F-test (p < 0.01) and the
Discussion
To elucidate the molecular bases of WD/CESD, it is very important to determine the conformational changes in human LAL associated with these diseases. Roussel et al. presented a three dimensional-model of wild type LAL and examined two partial deletions and three missense mutations [10]. But, to the best of our knowledge, there has been no comprehensive research on conformational changes in human LAL caused by amino acid substitutions leading to WD/CESD.
In this study, we investigated the
Acknowledgments
This work was supported by the Program for Research on Intractable Diseases of Health and Labor Science Research Grants (HS); the Program for the Promotion of Fundamental Studies in Health Sciences of the National Institute of Biomedical Innovation (ID: 09-15, HS); the JAPS Asia/Africa Scientific Platform Program (HS); the Japan Society for the Promotion of Science (JSPS ID: 21390314, HS); and the High-Tech Research Center Project of the Ministry of Education, Culture, Sports, Science and
References (20)
- et al.
Genetic and biochemical evidence that CESD and Wolman disease are distinguished by residual lysosomal acid lipase activity
Genomics
(1996) - et al.
Characterization of lysosomal acid lipase by site-directed mutagenesis and heterologous expression
J. Biol. Chem.
(1995) - et al.
New lysosomal acid lipase gene mutants explain the phenotype of Wolman disease and cholesteryl ester storage disease
J. Lipid Res.
(1998) - et al.
Lysosomal acid lipase mutations that determine phenotype in Wolman and cholesterol ester storage disease
Mol. Genet. Metab.
(1999) - et al.
Molecular defects underlying Wolman disease appear to be more heterogeneous than those resulting in cholesteryl ester storage disease
J. Lipid Res.
(1999) - et al.
Crystal structure of human gastric lipase and model of lysosomal acid lipase, two lipolytic enzymes of medical interest
J. Biol. Chem.
(1999) - et al.
Structural consequences of amino acid substitutions causing Tay–Sachs disease
Mol. Genet. Metab.
(2008) - et al.
Acid lipase deficiency: Wolman disease and cholesteryl ester storage disease
- et al.
Mutations at the lysosomal acid cholesteryl ester hydrolase gene locus in Wolman disease
Proc. Natl. Acad. Sci. U. S. A.
(1994) - et al.
Expression of lysosomal acid lipase mutants detected in three patients with cholesteryl ester storage disease
Hum. Mol. Genet.
(1996)
Cited by (28)
LC-MS/MS-based enzyme assay for lysosomal acid lipase using dried blood spots
2022, Molecular Genetics and Metabolism ReportsAISF update on the diagnosis and management of adult-onset lysosomal storage diseases with hepatic involvement
2020, Digestive and Liver DiseaseWolman disease
2020, Rosenberg’s Molecular and Genetic Basis of Neurological and Psychiatric Disease: Volume 1Update on lysosomal acid lipase deficiency: Diagnosis, treatment and patient management
2017, Medicina ClinicaChildhood/adult-onset lysosomal acid lipase deficiency: A serious metabolic and vascular phenotype beyond liver disease—four new pediatric cases
2017, Journal of Clinical LipidologyCitation Excerpt :Lysosomal acid lipase deficiency (LALD) is a rare autosomal recessive disease due to LIPA mutations.1,2
Expression and functional characterization of human lysosomal acid lipase gene (LIPA) mutation responsible for cholesteryl ester storage disease (CESD) phenotype
2015, Protein Expression and PurificationCitation Excerpt :The His295 residue is located on an alpha helix of the cap domain (residue 206–330) ∼13 Å away from the catalytic Ser174 in a hydrophobic pocket. It forms two hydrogen bonds with the Ser143 side chain and the Gln306 backbone of the core domain [12] and plays an important structural and functional role in holding the cap and core domains together. We speculate that the H295Y loss-of-function mutation, identified in CESD phenotype, will disrupt the hydrogen bond interaction between cap and core domains and thereby destabilize the protein.
- ☆
Disclosure: All authors declare no competing interest.
- 1
These authors equally contributed to this work.
- 2
Present address is Astellas Pharma Inc.