Hurler syndrome: a patient with abnormally high levels of alpha-L-iduronidase protein.
Mucopolysaccharidosis type I (MPS I: McKusick 25280) is a clinically heterogenous lysosomal storage disorder which is caused by a variable deficiency in alpha-L-iduronidase activity (alpha-L-iduronide iduronohydrolase, EC 3.2.1.76). Cultured fibroblasts from an MPS I patient (cell line 2827) with a severe clinical phenotype (Hurler syndrome) have been characterized using immunochemical and biochemical techniques. Using a specific immunoquantification assay, we have demonstrated that cell line 2827 had an alpha-L-iduronidase protein content (189 ng/mg of extracted cell protein) at least six times greater than the mean level found in normal control fibroblasts (30 ng/mg of extracted cell protein). This was the only MPS I cell line, from a group of 23 MPS I patients, that contained greater than 7% of the mean level of alpha-L-iduronidase protein detected in normal controls. Cell line 2827 had very low alpha-L-iduronidase activity toward the fluorogenic substrate 4-methylumbelliferyl-alpha-L-iduronide, and a radiolabeled disaccharide substrate derived from heparin. Maturation studies of alpha-L-iduronidase in cell line 2827 showed apparently normal levels of alpha-L-iduronidase synthesis with delayed processing to the mature form. Subcellular fractionation experiments demonstrated alpha-L-iduronidase protein in lysosomal-enriched fractions isolated from cell line 2827, suggesting a normal cell distribution and supporting the proposed delayed processing. It is proposed that the MPS I patient described has an alpha-L-iduronidase gene mutation which affects both the active site and post-translational processing of the enzyme. This mutation must be structurally conservative because it does not result in instability either during maturation or in the lysosome.
Brooks
D A
DA
Department of Chemical Pathology, Adelaide Children's Hospital, South Australia.
Harper
G S
GS
Gibson
G J
GJ
Ashton
L J
LJ
Taylor
J A
JA
McCourt
P A
PA
Freeman
C
C
Clements
P R
PR
Hoffmann
J W
JW
Hopwood
J J
JJ
D002478:Cells, Cultured; D002675:Child, Preschool; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007068:Iduronidase / Q000032:analysis*; D008247:Lysosomes / Q000201:enzymology; D008297:Male; D008059:Mucopolysaccharidosis I / Q000378:metabolism*; D011506:Proteins / Q000032:analysis*; D013347:Subcellular Fractions / Q000378:metabolism
D011506:Proteins; D007068:Iduronidase