Document Detail

Biosynthesis of the sulfatide/GM1 activator protein (SAP-1) in control and mutant cultured skin fibroblasts.
MedLine Citation:
PMID:  3081038     Owner:  NLM     Status:  MEDLINE    
Sphingolipid activator proteins (SAP) are relatively low-molecular-mass proteins that stimulate the hydrolysis of specific sphingolipids by the required lysosomal enzymes. SAP-1 or sulfatide/GM1 ganglioside activator protein has previously been demonstrated to stimulate the enzymatic hydrolysis of sulfatide, GM1 ganglioside and globotriaosylceramide. Using monospecific rabbit antibodies against human liver sulfatide/GM1 activator, the biosynthesis and processing of this activator were studied in cultured skin fibroblasts from controls and patients with GM1 gangliosidosis and a variant form of metachromatic leukodystrophy. When [35S]methionine was presented in the medium to control human fibroblasts for 4 h, the majority of the immunoprecipitable radiolabeling was confined to bands within three regions of apparent molecular mass 65-70, 35-52 and 8-13 kDa. The only immunoprecipitable radiolabeled species excreted into the medium when NH4Cl was present had an apparent molecular mass of 70 kDa. When the excretion products were given to fresh cells followed by incubation for up to 24 h there was production of the mature species. Treatment of the 70 kDa form with endoglycosidase F resulted in production of a 53 kDa molecular mass form. Pulse-chase experiments indicated that the initial immunoprecipitable translation product was 65 kDa which increased to 70 kDa over the next hour. The 65 kDa species must result from co-translational glycosylation of the polypeptide chain. Apparently, intralysosomal processing converts the 13 kDa form to the 8-11 kDa species. The cells from the patient with GM1 gangliosidosis could not process to the smallest species found in controls due to the deficiency of acid beta-galactosidase. Patients who have a variant form of metachromatic leukodystrophy do not make any immunoprecipitable radiolabeled products in the cells or in the media. This indicates a severe mutation in the gene coding for this activator protein. The production of such small mature species from a relatively large precursor form may regulate the production of this interesting protein.
S Fujibayashi; D A Wenger
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Biochimica et biophysica acta     Volume:  875     ISSN:  0006-3002     ISO Abbreviation:  Biochim. Biophys. Acta     Publication Date:  1986 Feb 
Date Detail:
Created Date:  1986-04-02     Completed Date:  1986-04-02     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  0217513     Medline TA:  Biochim Biophys Acta     Country:  NETHERLANDS    
Other Details:
Languages:  eng     Pagination:  554-62     Citation Subset:  IM    
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MeSH Terms
Cells, Cultured
Electrophoresis, Polyacrylamide Gel
Fibroblasts / metabolism*
G(M1) Ganglioside
Gangliosidoses / metabolism
Glycoside Hydrolases
Leukodystrophy, Metachromatic / metabolism
Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase
Methionine / metabolism
Mucolipidoses / metabolism
Protein Biosynthesis*
Proteins / genetics,  metabolism
Sphingolipid Activator Proteins
Grant Support
Reg. No./Substance:
0/Glycoproteins; 0/PSAP protein, human; 0/Proteins; 0/Saposins; 0/Sphingolipid Activator Proteins; 37758-47-7/G(M1) Ganglioside; 63-68-3/Methionine; EC 3.2.1.-/Glycoside Hydrolases; EC Endo-beta-N-Acetylglucosaminidase

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