Wolman’s disease: The Genetic Basis

1. Wolman’s disease: The Genetic Basis Deepasree Bangaru-Raju (Deepa) 17/5/2006

2. General Information • Gene Symbol : LIPA • Gene expressed at 5.1x than normal • Location : 10q • 99.5MB • This gene encodes lipase A, the lysosomal acid lipase (also known as cholesterol ester hydrolase). This enzyme functions in the lysosome to catalyze the hydrolysis of cholesteryl esters and triglycerides.

3. General structure of lipoprotein

4. FIGURE 12.7. Intracellular cholesterol metabolism. Low-density lipoprotein (LDL) is targeted to lysosomes by the LDL receptor and LDL cholesteryl esters are hydrolyzed to free cholesterol by the lysosomal acid lipase. The Niemann-Pick C gene 1 is required for transfer of lysosomal free cholesterol to the cytoplasmic pool. Free cholesterol can then be esterified to cholesteryl esters by acyl coenzyme A:cholesterol acyltransferase and stored as lipid droplets or be released to acceptor particles such as HDL. Free cholesterol within the cell down-regulates the expression of genes such as β-hydroxy-β-methylglutaryl-coenzyme A reductase and the LDL receptor. ACAT, acyl coenzyme A:cholesterol acyltransferase; CE, cholesteryl ester; FC, free cholesterol; NPC1, Niemann-Pick C gene 1.

5. The Protein

6. Genitic map • Deletions (7) and missense (14) mutations are abundant • There are no insertions and 6 nonsense mutation 100-120 60-80 180 267-289 311-333

7. Protein Sequence

8. Protein Sequence • Active Site 1: • Deletions in this region accounts for Ser-Thr rich motifs where glyosylation may occur • Ser is very important as it is part of Asp-Ser-His catalytic triad common to most lipases • LAL is a 378 amino acid protein containing 27 amino acid N-terminal signal peptide and 6 N-Glycosylation sites • N-linked carbohydrate residues is important for optimal activity. Val Gly His Ser Gln Gly Thr Thr Ile Gly

9. Catalytic Traid • Ser-Asp-His

10. Figure 3. Comparison of nucleotide sequences of PCR-amplified LAL cDNA from three WD subjects. A: Top, cDNA sequence of a normal individual at codons 102 to 109; bottom, mutation in subjects 1 and 2, showing a C deletion in nucleotide 398, leading to a premature stop codon in position 106 (S106X). Both subjects were homozygous for this nonsense mutation. B: Top, cDNA sequence of a normal subject at codons ;–9 to ;–3; bottom, mutation 1 of subject 3, showing a G-to-A transition mutation, leading to a substitution of Gly-5 by Arg (G-5R). C: Top, cDNA sequence of a normal subject at codons 57 to 63; bottom, mutation 2 of subject 3, showing a G-to-T transition, resulting in a Gly-to-Val missense mutation at codon 60 (G60V). Subject 3 was a compound homozygote for the G-5R and G60V mutations. All three mutations were verified in genomic DNA of the WD subjects. The positions of the mutations are boxed, and the amino acid residues generated by them are underlined. http://www.jlr.org/cgi/content/full/42/7/1033

11. Protein structure Sequence Model Coverage (including SNP positions)

12. Protein structure (2)

13. Protein structure (3)

14. Protein Structure (4)

15. Protein structure (5)

16. Pathway

17. Pathway (2)

18. Pathway (3)

19. Organs affected by the disease Normal Healthy Liver Wolman Liver

20. Organs affected by the disease Normal Healthy Kidney Wolman Kidney