Glucocerebrosidase Explained

β-Glucocerebrosidase (also called acid β-glucosidase, D-glucosyl-N-acylsphingosine glucohydrolase, or GCase) is an enzyme with glucosylceramidase activity that cleaves by hydrolysis the β-glycosidic linkage of the chemical glucocerebroside, an intermediate in glycolipid metabolism that is abundant in cell membranes (particularly skin cells).[1] It is localized in the lysosome, where it remains associated with the lysosomal membrane.[2] β-Glucocerebrosidase is 497 amino acids in length and has a molecular mass of 59,700 Da.

Structure

β-Glucocerebrosidase is a member of the glycoside hydrolase family 30 and consists of three distinct domains (I-III).[3] Domain I (residues 1–27 and 383–414) forms a three-stranded anti-parallel β-sheet. This domain contains two disulfide bridges that are necessary for correct folding, as well as a glycosylated residue (Asn19) that is required for catalytic activity in vivo. Domain II (residues 30–75 and 431–497) consists of two β-sheets that resemble an immunoglobulin fold. Domain III (residues 76–381 and 416–430) is homologous to a TIM barrel and is a highly conserved domain among glycoside hydrolases.[4] Domain III harbors the active site, which binds the substrate glucocerebroside in close proximity to the catalytic residues E340 and E235. Domains I and III are tightly associated, while domains II and III are joined by a disordered linker.

Mechanism

Crystal structures indicate that β-glucocerebrosidase binds the glucose moiety and adjacent O-glycosydic bond of glucocerebroside. The two aliphatic chains of glucocerebroside may remain associated with the lysosomal bilayer or interact with the activating protein Saposin C.

Consistent with other glycoside hydrolases, the mechanism of glucocerebroside hydrolysis by β-glucocerebrosidase involves acid/base catalysis by two glutamic acid residues (E340 and E235) and precedes through a two-step mechanism. In the first step, E340 performs a nucleophilic attack at the carbon of the O-glycosidic linkage to displace the sphingosine moiety, which is simultaneously protonated by E235 as it is released from the active site. In the second step, glucose is hydrolyzed from the E340 residue to regenerate the active enzyme.[5]

Properties

β-Glucocerebrosidase is maximally active at pH 5.5, the pH of the lysosomal compartment.[6] Within the lysosome it remains associated with the membrane, where it binds and degrades its substrate glucocerebroside (GluCer). It requires the activating protein Saposin C as well as negatively charged lipids for maximal catalytic activity.[7] [8] The role of Saposin C is not known; however, it is shown to bind both the lysosomal membrane and the lipid moieties of GluCer, and therefore may recruit GluCer to the active site of the enzyme.[9] [10]

β-Glucocerebrosidase is specifically and irreversibly inhibited by the glucose analog Conduritol B epoxide. Conduritol B epoxide binds to the GCase active site, where the enzyme cleaves its epoxide ring, forming a permanent covalent bond between the enzyme and the inhibitor.[11]

Initially, GCase was thought to be one of the few lysosomal enzymes that does not follow the mannose-6-phosphate pathway for trafficking to the lysosome.[12] A study in I-cell disease fibroblasts (in which the phosphotransferase that puts Mannose 6-phosphate on proteins to target them to the lysosome is defective) showed targeting of GCase to the lysosome independent of the M6P pathway.[13] The lysosomal transporter and integral membrane protein LIMP-2 (Lysosomal Integral Membrane Protein 2) was shown to bind GCase and facilitate transport to the lysosome, demonstrating a mechanism for M6P-independent lysosomal trafficking. This conclusion was called into question when a crystal structure of GCase in complex with LIMP-2 showed a Mannose 6-phosphate moiety on LIMP-2, suggesting the complex can also follow the traditional mannose-6-phosphate pathway.[14]

Clinical significance

Mutations in the glucocerebrosidase gene cause Gaucher's disease, a lysosomal storage disease characterized by an accumulation of glucocerebrosides in macrophages that infiltrate many vital organs.[15] [16]

Mutations in the glucocerebrosidase gene are also associated with Parkinson's disease.[17] [18]

A related pseudogene is approximately 12 kb downstream of this gene on chromosome 1. Alternative splicing results in multiple transcript variants encoding the same protein.[19]

Drugs

Alglucerase (Ceredase) was a version of glucocerebrosidase that was harvested from human placental tissue and then modified with enzymes.[20] It was approved by the FDA in 1991[21] but has been withdrawn from the market[22] [23] due to the approval of similar drugs made with recombinant DNA technology instead of being harvested from tissue. Drugs made recombinantly pose no risk of diseases being transmitted from the tissue used in harvesting, and are less expensive to manufacture.[20]

Recombinant glucocerebrosidases used as drugs include:[24]

See also

Further reading

External links

Notes and References

  1. Vielhaber G, Pfeiffer S, Brade L, Lindner B, Goldmann T, Vollmer E, Hintze U, Wittern KP, Wepf R . Localization of ceramide and glucosylceramide in human epidermis by immunogold electron microscopy . The Journal of Investigative Dermatology . 117 . 5 . 1126–36 . November 2001 . 11710923 . 10.1046/j.0022-202x.2001.01527.x . free .
  2. Rijnboutt S, Aerts HM, Geuze HJ, Tager JM, Strous GJ . Mannose 6-phosphate-independent membrane association of cathepsin D, glucocerebrosidase, and sphingolipid-activating protein in HepG2 cells . The Journal of Biological Chemistry . 266 . 8 . 4862–8 . March 1991 . 10.1016/S0021-9258(19)67728-8 . 1848227 . free . 1887/50559 . free .
  3. Lieberman RL . A Guided Tour of the Structural Biology of Gaucher Disease: Acid-β-Glucosidase and Saposin C . Enzyme Research . 2011 . 973231 . 2011 . 22145077 . 3226326 . 10.4061/2011/973231 . free .
  4. Rigden DJ, Jedrzejas MJ, de Mello LV . Identification and analysis of catalytic TIM barrel domains in seven further glycoside hydrolase families . FEBS Letters . 544 . 1–3 . 103–11 . June 2003 . 12782298 . 10.1016/S0014-5793(03)00481-2 . free .
  5. Vocadlo DJ, Davies GJ, Laine R, Withers SG . Catalysis by hen egg-white lysozyme proceeds via a covalent intermediate . Nature . 412 . 6849 . 835–8 . August 2001 . 11518970 . 10.1038/35090602 . 2001Natur.412..835V . 205020153 .
  6. Sinclair G, Pfeifer TA, Grigliatti TA, Choy FY . Secretion of human glucocerebrosidase from stable transformed insect cells using native signal sequences . Biochemistry and Cell Biology . 84 . 2 . 148–56 . April 2006 . 16609695 . 10.1139/o05-165 .
  7. Aerts JM, Sa Miranda MC, Brouwer-Kelder EM, Van Weely S, Barranger JA, Tager JM . Conditions affecting the activity of glucocerebrosidase purified from spleens of control subjects and patients with type 1 Gaucher disease . Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology . 1041 . 1 . 55–63 . October 1990 . 2223847 . 10.1016/0167-4838(90)90122-V .
  8. Weiler S, Kishimoto Y, O'Brien JS, Barranger JA, Tomich JM . Identification of the binding and activating sites of the sphingolipid activator protein, saposin C, with glucocerebrosidase . Protein Science . 4 . 4 . 756–64 . April 1995 . 7613473 . 2143096 . 10.1002/pro.5560040415 .
  9. Alattia JR, Shaw JE, Yip CM, Privé GG . Direct visualization of saposin remodelling of lipid bilayers . Journal of Molecular Biology . 362 . 5 . 943–53 . October 2006 . 16949605 . 10.1016/j.jmb.2006.08.009 .
  10. Tamargo RJ, Velayati A, Goldin E, Sidransky E . The role of saposin C in Gaucher disease . Molecular Genetics and Metabolism . 106 . 3 . 257–63 . July 2012 . 22652185 . 3534739 . 10.1016/j.ymgme.2012.04.024 .
  11. Ogawa S, Uetsuki S, Tezuka Y, Morikawa T, Takahashi A, Sato K . Synthesis and evaluation of glucocerebrosidase inhibitory activity of anhydro deoxyinositols from (+)-epi- and (-)-vibo-quercitols . Bioorganic & Medicinal Chemistry Letters . 9 . 11 . 1493–8 . June 1999 . 10386923 . 10.1016/S0960-894X(99)00223-1 .
  12. Reczek D, Schwake M, Schröder J, Hughes H, Blanz J, Jin X, Brondyk W, Van Patten S, Edmunds T, Saftig P . LIMP-2 is a receptor for lysosomal mannose-6-phosphate-independent targeting of beta-glucocerebrosidase . en . Cell . 131 . 4 . 770–83 . November 2007 . 18022370 . 10.1016/j.cell.2007.10.018 . 6771697 . free .
  13. Glickman JN, Kornfeld S . Mannose 6-phosphate-independent targeting of lysosomal enzymes in I-cell disease B lymphoblasts . The Journal of Cell Biology . 123 . 1 . 99–108 . October 1993 . 8408210 . 2119824 . 10.1083/jcb.123.1.99 .
  14. Zhao Y, Ren J, Padilla-Parra S, Fry EE, Stuart DI . Lysosome sorting of β-glucocerebrosidase by LIMP-2 is targeted by the mannose 6-phosphate receptor . Nature Communications . 5 . 4321 . July 2014 . 25027712 . 4104448 . 10.1038/ncomms5321 . 2014NatCo...5.4321Z .
  15. Mucci JM, Rozenfeld P . Pathogenesis of Bone Alterations in Gaucher Disease: The Role of Immune System . Journal of Immunology Research . 2015 . 192761 . 2015 . 26064996 . 4433682 . 10.1155/2015/192761 . free .
  16. Stirnemann J, Belmatoug N, Camou F, Serratrice C, Froissart R, Caillaud C, Levade T, Astudillo L, Serratrice J, Brassier A, Rose C, Billette de Villemeur T, Berger MG . A Review of Gaucher Disease Pathophysiology, Clinical Presentation and Treatments . International Journal of Molecular Sciences . 18 . 2 . 441 . February 2017 . 28218669 . 5343975 . 10.3390/ijms18020441 . free .
  17. Kalia LV, Lang AE . Parkinson's disease . Lancet . 386 . 9996 . 896–912 . August 2015 . 25904081 . 10.1016/S0140-6736(14)61393-3 . 5502904 .
  18. Web site: PhD . Lindsey Shapiro . 2023-09-18 . Researchers win Breakthrough Prize for Parkinson's genetics discoveries Parkinson's News Today . 2023-09-20 . parkinsonsnewstoday.com . en-US.
  19. Web site: Entrez Gene: GBA glucosidase, beta; acid (includes glucosylceramidase).
  20. Deegan PB, Cox TM . Imiglucerase in the treatment of Gaucher disease: a history and perspective . Drug Design, Development and Therapy . 6 . 81–106 . 2012 . 22563238 . 3340106 . 10.2147/DDDT.S14395 . free .
  21. Regulatory Matters . https://web.archive.org/web/20051108094021/http://whqlibdoc.who.int/druginfo/DRUG_INFO_5_3_1991_p122-125.pdf . dead . 8 November 2005 . WHO Drug Information . 1991 . 5 . 3 . 123–4 .
  22. Web site: Enzyme-replacement Therapy for Lysosomal Storage Disorders . Clinical Policy Bulletin Number: 0442 . Aetna . 2014-08-08 .
  23. Web site: FDA Prescription and Over-the-Counter Drug Product List . U.S. Food and Drug Administration . Additions/Deletions for Prescription Drug Product List . March 2012 .
  24. Grabowski GA . Gaucher disease and other storage disorders . Hematology. American Society of Hematology. Education Program . 2012 . 13–8 . 2012 . 23233555 . 10.1182/asheducation.v2012.1.13.3797921. free .
  25. News: Yukhananov . Anna . U.S. FDA approves Pfizer/Protalix drug for Gaucher . 2 May 2012. Chicago Tribune. 1 May 2012. Reuters.

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