Klotho-related Protein Is a Novel Cytosolic Neutral β-Glycosylceramidase

Abstract

Using C6-NBD-glucosylceramide (GlcCer) as a substrate, we detected the activity of a conduritol B epoxide-insensitive neutral glycosylceramidase in cytosolic fractions of zebrafish embryos, mouse and rat brains, and human fibroblasts. The candidates for the enzyme were assigned to the Klotho (KL), whose family members share a ␤-glucosidase-like domain but whose natural substrates are unknown. Among this family, only the KL-related protein (KLrP) is capable of degrading C6-NBDGlcCer when expressed in CHOP cells, in which Myc-tagged KLrP was exclusively distributed in the cytosol. In addition, knockdown of the endogenous KLrP by small interfering RNA increased the cellular level of GlcCer. The purified recombinant KLrP hydrolyzed 4-methylumbelliferyl-glucose, C6-NBD-GlcCer, and authentic GlcCer at pH 6.0. The enzyme also hydrolyzed the corresponding galactosyl derivatives, but each k cat /K m was much lower than that for glucosyl derivatives. The x-ray structure of KLrP at 1.6 Å resolution revealed that KLrP is a (␤/␣) 8 TIM barrel, in which Glu 165 and Glu 373 at the carboxyl termini of ␤-strands 4 and 7 could function as an acid/base catalyst and nucleophile, respectively. The substrate-binding cleft of the enzyme was occupied with palmitic acid and oleic acid when the recombinant protein was crystallized in a complex with glucose. GlcCer was found to fit well the cleft of the crystal structure of KLrP. Collectively, KLrP was identified as a cytosolic neutral glycosylceramidase that could be involved in a novel nonlysosomal catabolic pathway of GlcCer.

Involvement of Acid β-Glucosidase 1 in the Salvage Pathway of Ceramide Formation

“…On the other hand, in addition to lysosomal GBA1, neutral glucocerebrosidases have been cloned and characterized as GBA2 (33,34) and Klotho-related protein (35), and they differ in a number of characteristics from GBA1, such as sensitivity to conduritol B epoxide, optimal pH, and cellular localization. In light of these distinct characteristics, neutral glucocerebrosidases are unlikely to play a role in lysosomal catabolism of glucosylceramide followed by generating lysosomal ceramide.…”

Structural and Enzymatic Characterization of Os3BGlu6, a Rice β-Glucosidase Hydrolyzing Hydrophobic Glycosides and (1→3)- and (1→2)-Linked Disaccharides

“…Simplified phylogenetic tree of the amino acid sequences of eukaryotic GH1 proteins with known structures and those of rice and Arabidopsis GH1 gene products. The protein sequences of the eukaryotic proteins with known structures are marked with four-character PDB codes for one of their structures, including Trifolium repens cyanogenic b-glucosidase (1CBG; Barrett et al, 1995), Sinapsis alba myrosinase (1MYR; Burmeister et al, 1997), Zea mays ZmGlu1 b-glucosidase (1E1F; Czjzek et al, 2000), Sorghum bicolor Dhr1 dhurrinase (1V02; Verdoucq et al, 2004), Triticum aestivum b-glucosidase (2DGA; Sue et al, 2006), Rauvolfia serpentina strictosidine b-glucosidase (2JF6; Barleben et al, 2007), and Oryza sativa Os3BGlu7 (BGlu1) b-glucosidase (2RGL; Chuenchor et al, 2008) from plants, along with Brevicoryne brassicae myrosinase (1WCG; Husebye et al, 2005), Homo sapiens cytoplasmic (Klotho) b-glucosidase (2E9M; Hayashi et al, 2007), and Phanerochaete chrysosporium (2E3Z; Nijikken et al, 2007), while those encoded in the Arabidopsis and rice genomes are labeled with the systematic names given by Xu et al (2004) and Opassiri et al (2006), respectively. One or two example proteins from each plant are given for each of the eight clusters of genes shared by Arabidopsis (At) and rice (Os) and the Arabidopsis-specific clusters At I (b-glucosidases) and At II (myrosinases), with the number of Arabidopsis or rice enzymes in each cluster given in parentheses.…”

Encephalopathy Caused by Ablation of Very Long Acyl Chain Ceramide Synthesis May Be Largely Due to Reduced Galactosylceramide Levels

“…Enzyme Activities-Enzyme activities were determined as follows: CerS2 using D-erythro- [4, H]sphinganine and C24-acyl-CoA (12,24); neutral and acid sphingomyelinase using C6-NBD-SM (14,25,26); galactosylceramidase using C6-NBD-GalCer (27); and hexosaminidase A, ␣-galactosidase, ␤-glucuronidase, ␣-mannosidase, ␤-mannosidase, and p-nitrocatechol sulfate using 4-methylumbelliferone (28 -30). Gangliosides were purified (31) after isolation from the upper phase (32), separated by thin layer chromatography using chloroform, methanol, 0.2% CaCl 2 (55:45:10) as the developing solvent, and stained using resorcinol (33).…”