Kolesterolin (Chol) transgalaktosyloituminen (GalChol) ja transglykosyloituminen (GlcChol)

 

Glucocerebrosidases (GBA)  catalyze a transgalactosylation reaction that yields a newly-identified brain sterol metabolite, galactosylated cholesterol.

Akiyama H, Ide M, Nagatsuka Y, Sayano T, Nakanishi E, Uemura N, Yuyama K, Yamaguchi Y, Kamiguchi H, Takahashi R, Aerts JMFG, Greimel P, Hirabayashi Y. J Biol Chem. 2020 Apr 17;295(16):5257-5277. doi: 10.1074/jbc.RA119.012502. Epub 2020 Mar 6. PMID: 32144204 Free PMC article.

β-Glucocerebrosidase (GBA) hydrolyzes glucosylceramide (GlcCer) to generate ceramide(Cer). Previously, we demonstrated that lysosomal GBA1 and nonlysosomal GBA2 possess not only GlcCer hydrolase activity, but also transglucosylation activity to transfer the glucose residue from GlcCer to cholesterol to form β-cholesterylglucoside (β-GlcChol) in vitro β-GlcChol is a member of sterylglycosides present in diverse species. 

How GBA1 and GBA2 mediate β-GlcChol metabolism in the brain is unknown. 

 Here, we purified and characterized sterylglycosides from rodent and fish brains. Although glucose is thought to be the sole carbohydrate component of sterylglycosides in vertebrates, structural analysis of rat brain sterylglycosides revealed the presence of galactosylated cholesterol (β-GalChol), in addition to β-GlcChol. 

Analyses of brain tissues from GBA2-deficient mice and GBA1- and/or GBA2-deficient Japanese rice fish (Oryzias latipes) revealed that GBA1 and GBA2 are responsible for β-GlcChol degradation and formation, respectively, and that both GBA1 and GBA2 are responsible for β-GalChol formation. 

 Liquid chromatography-tandem MS revealed that β-GlcChol and β-GalChol are present throughout development from embryo to adult in the mouse brain. We found that β-GalChol expression depends on galactosylceramide (GalCer), and developmental onset of β-GalChol biosynthesis appeared to be during myelination.

 We also found that β-GlcChol and β-GalChol are secreted from neurons and glial cells in association with exosomes. 

In vitro enzyme assays confirmed that GBA1 and GBA2 have transgalactosylation activity to transfer the galactose residue from GalCer to cholesterol to form β-GalChol. This is the first report of the existence of β-GalChol in vertebrates and how β-GlcChol and β-GalChol are formed in the brain.

Keywords: brain; cholesterol; galactosylated cholesterol; glucocerebrosidase; glycolipid; mass spectrometry (MS); sterol; sterylglycoside; transglycosylation; β-cholesterylgalactoside

GBA1, GBA2 ja GBA3, glukosyylikeramidaasien perhe

GBA1  (1q22)  Lysosomaalinen glykosyylikeramidaasi, Glukokerebrosidaasi

 https://www.genecards.org/cgi-bin/carddisp.pl?gene=GBA1&keywords=GBA1

GBA2 (9p13.3) Non-lysosomaalinen glykosyylikeramidaasi

 https://www.genecards.org/cgi-bin/carddisp.pl?gene=GBA2&keywords=GBA2

GBA3  (4p15.2), Sytosolinen glukosyylikeramidaasi beeta 3  pystyy käsittelemään dietäärisiä glykosyyliyhdisteitäkin.

https://www.genecards.org/cgi-bin/carddisp.pl?gene=GBA3&keywords=GBA3

Entrez Gene Summary for GBA3 Gene

• The protein encoded by this gene is a cytosolic enzyme that can hydrolyze several types of glycosides. The enzyme has its highest activity at neutral pH and is predominantly expressed in human liver, kidney, intestine, and spleen. This gene is a polymorphic pseudogene, with the most common allele being the functional allele that encodes the full-length protein. Some individuals contain a single nucleotide polymorphism that results in a premature stop codon in the coding region, and therefore this allele is pseudogenic due to the failure to produce a functional full-length protein. Alternative splicing of this gene results in multiple transcript variants. [provided by RefSeq, Apr 2022]

GeneCards Summary for GBA3 Gene

GBA3 (Glucosylceramidase Beta 3 (Gene/Pseudogene)) is a Protein Coding gene. Diseases associated with GBA3 include Gaucher's Disease. Among its related pathways are Sphingolipid metabolism and Metabolism. Gene Ontology (GO) annotations related to this gene include hydrolase activity, hydrolyzing O-glycosyl compounds and beta-glucosidase activity. An important paralog of this gene is LCT.

UniProtKB/Swiss-Prot Summary for GBA3 Gene

Neutral cytosolic beta-glycosidase with a broad substrate specificity that could play a role in the catabolism of glycosylceramides (PubMed:11389701, 11784319, 20728381, 26724485, 17595169, 33361282). Has a significant glucosylceramidase activity in vitro (PubMed:26724485, 17595169). However, that activity is relatively low and its significance in vivo is not clear (PubMed:26724485, 17595169, 20728381). Hydrolyzes galactosylceramides/GalCers, glucosylsphingosines/GlcSphs and galactosylsphingosines/GalSphs (PubMed:17595169). However, the in vivo relevance of these activities is unclear (PubMed:17595169). It can also hydrolyze a broad variety of dietary glycosides including phytoestrogens, flavonols, flavones, flavanones and cyanogens in vitro and could therefore play a role in the metabolism of xenobiotics (PubMed:11784319). Possesses transxylosylase activity in vitro using xylosylated ceramides/XylCers (such as beta-D-xylosyl-(1<->1')-N-acylsphing-4-enine) as xylosyl donors and cholesterol as acceptor (PubMed:33361282). Could also play a role in the catabolism of cytosolic sialyl free N-glycans (PubMed:26193330). ( GBA3_HUMAN,Q9H227 )

Tocris Summary for GBA3 Gene

• Glycosylases are a group of enzymes that includes glucosidases, mannosidases and heparanases. There are two glucosidase subtypes, both found in the gut. They hydrolyze terminal (1,4)alpha-glucosidic linkages and (1,6)beta-glucosidic linkages, liberating alpha-glucose and beta-glucose.

GlcCer, GalCer , geramide, glukosyl, galaktosyl , GBA1 ja GBA2 transglykosyloivat ja myös transgalaktosyloivat , GlcChol, GalChol

 AIEMPI tekstini:

Synteesi KERAMIDISTA kohti glykosfingolipidejä.KERAMIDI (Cer) syntyy endoplasmisessa retikulumissa ja se kulkeutuu Golgin laitteeseen.. Keramidia purkautuu myös sfingolipidien kataboliasta ja käytetään uudestaan.

GlcCer, glucosylceramide, glukosyylikeramidi

GlcCer syntaasientsyymi lisää glukoosin beta-sidoksella keramidin OH- ryhmään 1- asemassa.Glukosyylikeramidiin tapahtuva jatkosyntetisoiminen tapahtuu sen jälkeen kun karakterisoimattoman flippaasi-entsyymin avulla on tapahtunut vaihde Golgin laitteen ontelon puolelle.

http://link.springer.com/chapter/10.1007%2F978-4-431-67877-9_1#page-1

GalCer, galactosylceramide, galaktosyylikeramidi muodostusta voi myös joskus tapahtua keramidista. Tämä tapahtuu endoplasmisen retikulumin ontelon puolella, vaikkakin galaktosyylikeramidien synteesitietä tapahtuu vain hyvin rajoitetusti.

http://link.springer.com/chapter/10.1007%2F978-4-431-67877-9_8#page-1

PÄIVITYSTÄ GlcCer ja GalCer synteesiasiaan  11.5. 2023

On uudempaa tietoa on GlcCer ja GalCer muodostumisesta aineenvaihdunnassa vuodelta 2020

https://www.jbc.org/article/S0021-9258(17)48548-6/fulltext

β-Glucocerebrosidase (GBA) hydrolyzes glucosylceramide (GlcCer) to generate ceramide. Previously, we demonstrated that lysosomal GBA1 and nonlysosomal GBA2 possess not only GlcCer hydrolase activity, but also transglucosylation activity to transfer the glucose residue from GlcCer to cholesterol to form β-cholesterylglucoside (β-GlcChol) in vitro. β-GlcChol is a member of sterylglycosides present in diverse species. How GBA1 and GBA2 mediate β-GlcChol metabolism in the brain is unknown. Here, we purified and characterized sterylglycosides from rodent and fish brains. Although glucose is thought to be the sole carbohydrate component of sterylglycosides in vertebrates, structural analysis of rat brain sterylglycosides revealed the presence of galactosylated cholesterol (β-GalChol), in addition to β-GlcChol. Analyses of brain tissues from GBA2-deficient mice and GBA1- and/or GBA2-deficient Japanese rice fish (Oryzias latipes) revealed that GBA1 and GBA2 are responsible for β-GlcChol degradation and formation, respectively, and that both GBA1 and GBA2 are responsible for β-GalChol formation. Liquid chromatography–tandem MS revealed that β-GlcChol and β-GalChol are present throughout development from embryo to adult in the mouse brain.

We found that β-GalChol expression depends on galactosylceramide (GalCer), and developmental onset of β-GalChol biosynthesis appeared to be during myelination. We also found that β-GlcChol and β-GalChol are secreted from neurons and glial cells in association with exosomes.

In vitro enzyme assays confirmed that GBA1 and GBA2 have transgalactosylation activity to transfer the galactose residue from GalCer to cholesterol to form β-GalChol. This is the first report of the existence of β-GalChol in vertebrates and how β-GlcChol and β-GalChol are formed in the brain.