5nxb

Structural highlights

Disease

[GALC_MOUSE] Defects in Galc are the cause of the 'twitcher' phenotype; an autosomal recessive leukodystrophy similar to the human disease (Krabbe disease). This deficiency results in the insufficient catabolism of several galactolipids that are important in the production of normal myelin.

Function

[GALC_MOUSE] Hydrolyzes the galactose ester bonds of galactosylceramide, galactosylsphingosine, lactosylceramide, and monogalactosyldiglyceride. Enzyme with very low activity responsible for the lysosomal catabolism of galactosylceramide, a major lipid in myelin, kidney and epithelial cells of small intestine and colon.^[1] [SAP_MOUSE] Prosaposin: Behaves as a myelinotrophic and neurotrophic factor, these effects are mediated by its G-protein-coupled receptors, GPR37 and GPR37L1, undergoing ligand-mediated internalization followed by ERK phosphorylation signaling.^[2] Saposin-A and saposin-C stimulate the hydrolysis of glucosylceramide by beta-glucosylceramidase (EC 3.2.1.45) and galactosylceramide by beta-galactosylceramidase (EC 3.2.1.46). Saposin-C apparently acts by combining with the enzyme and acidic lipid to form an activated complex, rather than by solubilizing the substrate.[UniProtKB:P07602] Saposin-B stimulates the hydrolysis of galacto-cerebroside sulfate by arylsulfatase A (EC 3.1.6.8), GM1 gangliosides by beta-galactosidase (EC 3.2.1.23) and globotriaosylceramide by alpha-galactosidase A (EC 3.2.1.22). Saposin-B forms a solubilizing complex with the substrates of the sphingolipid hydrolases.[UniProtKB:P07602] Saposin-D is a specific sphingomyelin phosphodiesterase activator (EC 3.1.4.12).[UniProtKB:P07602] Saposins are specific low-molecular mass non-enzymic proteins, they participate in the lysosomal degradation of sphingolipids, which takes place by the sequential action of specific hydrolases.[UniProtKB:P07602]

References

1. ↑ Sakai N, Inui K, Tatsumi N, Fukushima H, Nishigaki T, Taniike M, Nishimoto J, Tsukamoto H, Yanagihara I, Ozono K, Okada S. Molecular cloning and expression of cDNA for murine galactocerebrosidase and mutation analysis of the twitcher mouse, a model of Krabbe's disease. J Neurochem. 1996 Mar;66(3):1118-24. PMID:8769874
2. ↑ Meyer RC, Giddens MM, Schaefer SA, Hall RA. GPR37 and GPR37L1 are receptors for the neuroprotective and glioprotective factors prosaptide and prosaposin. Proc Natl Acad Sci U S A. 2013 Jun 4;110(23):9529-34. doi:, 10.1073/pnas.1219004110. Epub 2013 May 20. PMID:23690594 doi:http://dx.doi.org/10.1073/pnas.1219004110