Protein O-GlcNAcase explained

Protein O-GlcNAcase (OGA, glycoside hydrolase O-GlcNAcase, O-GlcNAcase, BtGH84, O-GlcNAc hydrolase) is an enzyme with systematic name (protein)-3-O-(N-acetyl-D-glucosaminyl)-L-serine/threonine N-acetylglucosaminyl hydrolase.[1] [2] [3] [4] [5] OGA is encoded by the OGA gene. This enzyme catalyses the removal of the O-GlcNAc post-translational modification in the following chemical reaction:

  1. [protein]-3-O-(N-acetyl-β-D-glucosaminyl)-L-serine + H2O [protein]-L-serine + N-acetyl-D-glucosamine
  2. [protein]-3-O-(N-acetyl-β-D-glucosaminyl)-L-threonine + H2O [protein]-L-threonine + N-acetyl-D-glucosamine

Nomenclature

Protein O-GlcNAcase
Ec Number:3.2.1.169
Align:left

Other names include:

Isoforms

The human OGA gene is capable of producing two different transcripts, each capable of encoding a different OGA isoform. The long isoform L-OGA, a bifunctional enzyme that possess a glycoside hydrolase activity and a pseudo histone-acetyl transferase domain, primarily resides in the cytoplasm and the nucleus. The short isoform S-OGA, which only exhibit the glycoside hydrolase domain, was initially described as residing within the nucleus. However, more recent work showed that S-OGA is located in mitochondria and regulates reactive oxygen production in this organelle.[6] Another isoform, resulting from proteolytic cleavage of L-OGA, has also been described. All three isoforms exhibit glycoside hydrolase activity.[7]

Homologs

Protein O-GlcNAcases belong to glycoside hydrolase family 84 of the carbohydrate active enzyme classification.[8] Homologs exist in other species as O-GlcNAcase is conserved in higher eukaryotic species. In a pairwise alignment, humans share 55% homology with Drosophila and 43% with C. elegans. Drosophila and C. elegans share 43% homology. Among mammals, the OGA sequence is even more highly conserved. The mouse and the human have 97.8% homology. However, OGA does not share significant homology with other proteins. However, short stretches of about 200 amino acids in OGA have homology with some proteins such as hyaluronidase, a putative acetyltransferase, eukaryotic translation elongation factor-1γ, and the 11-1 polypeptide.[9]

Reaction

Protein O-GlcNAcylation

See main article: O-GlcNAc. O-GlcNAcylation is a form of glycosylation, the site-specific enzymatic addition of saccharides to proteins and lipids. This form of glycosylation is with O-linked β-N-acetylglucosamine or β-O-linked 2-acetamido-2-deoxy-D-glycopyranose (O-GlcNAc). In this form, a single sugar (β-N-acetylglucosamine) is added to serine and threonine residues of nuclear or cytoplasmic proteins. Two conserved enzymes control this glycosylation of serine and threonine: O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). While OGT catalyzes the addition of O-GlcNAc to serine and threonine, OGA catalyzes the hydrolytic cleavage of O-GlcNAc from post-transitionally modified proteins.[10]

OGA is a member of the family of hexosaminidases. However, unlike lysosomal hexosaminidases, OGA activity is the highest at neutral pH (approximately 7) and it localizes mainly to the cytosol. OGA and OGT are synthesized from two conserved genes and are expressed throughout the human body with high levels in the brain and pancreas. The products of O-GlcNAc and the process itself plays a role in embryonic development, brain activity, hormone production, and a myriad of other activities.[11] [12]

Over 600 proteins are targets for O-GlcNAcylation. While the functional effects of O-GlcNAc modification is not fully known, it is known that O-GlcNAc modification impacts many cellular activities such as lipid/carbohydrate metabolism and hexosamine biosynthesis. Modified proteins may modulate various downstream signaling pathways by influencing transcription and proteomic activities.[13]

Mechanism and inhibition

OGA catalyzes O-GlcNAc hydrolysis via an oxazoline reaction intermediate.[14] Stable compounds which mimic the reaction intermediate can act as selective enzyme inhibitors. Thiazoline derivatives of GlcNAc can be used as a reaction intermediate. An example of this includes Thiamet-G as shown on the right. A second form of inhibition can occur from the mimicry of the transition state. The GlcNAcstatin family of inhibitors exploit this mechanism in order to inhibit OGA activity. For both types of inhibitors, OGA can be selected apart from the generic lysosomal hexosaminidases by elongating the C2 substituent in their chemical structure. This takes advantage of a deep pocket in OGA's active site that allow it to bind analogs of GlcNAc.[15]

There is potential for regulation of O-GlcNAcase for the treatment of Alzheimer's disease. When the tau protein in the brain is hyperphosphorylated, neurofibrillary tangles form, which are a pathological hallmark for neurodegenerative diseases such as Alzheimer's disease. In order to treat this condition, OGA is targeted by inhibitors such as Thiamet-G in order to prevent O-GlcNAc from being removed from tau, which assists in preventing tau from becoming phosphorylated.[16]

Structure

X-ray structures are available for a range of O-GlcNAcase proteins. The X-ray structure of human O-GlcNAcase in complex with Thiamet-G identified the structural basis of enzyme inhibition.[17]

See also

Further reading

Notes and References

  1. Wells L, Gao Y, Mahoney JA, Vosseller K, Chen C, Rosen A, Hart GW . Dynamic O-glycosylation of nuclear and cytosolic proteins: further characterization of the nucleocytoplasmic beta-N-acetylglucosaminidase, O-GlcNAcase . The Journal of Biological Chemistry . 277 . 3 . 1755–61 . January 2002 . 11788610 . 10.1074/jbc.M109656200 . free .
  2. Cetinbaş N, Macauley MS, Stubbs KA, Drapala R, Vocadlo DJ . Identification of Asp174 and Asp175 as the key catalytic residues of human O-GlcNAcase by functional analysis of site-directed mutants . Biochemistry . 45 . 11 . 3835–44 . March 2006 . 16533067 . 10.1021/bi052370b .
  3. Dennis RJ, Taylor EJ, Macauley MS, Stubbs KA, Turkenburg JP, Hart SJ, Black GN, Vocadlo DJ, Davies GJ . 6 . Structure and mechanism of a bacterial beta-glucosaminidase having O-GlcNAcase activity . Nature Structural & Molecular Biology . 13 . 4 . 365–71 . April 2006 . 16565725 . 10.1038/nsmb1079 . 9239755 .
  4. Kim EJ, Kang DO, Love DC, Hanover JA . Enzymatic characterization of O-GlcNAcase isoforms using a fluorogenic GlcNAc substrate . Carbohydrate Research . 341 . 8 . 971–82 . June 2006 . 16584714 . 10.1016/j.carres.2006.03.004 . 10561171 .
  5. Dong DL, Hart GW . Purification and characterization of an O-GlcNAc selective N-acetyl-beta-D-glucosaminidase from rat spleen cytosol . The Journal of Biological Chemistry . 269 . 30 . 19321–30 . July 1994 . 10.1016/S0021-9258(17)32170-1 . 8034696 . free .
  6. Pagesy P, Bouaboud A, Feng Z, Hulin P, Issad T . Short O-GlcNAcase is targeted to the mitochondria and regulates mitochondrial reactive oxygen species level . Cells . 11 . 11 . 1827 . June 2022 . 35681522 . 10.3390/cells11111827 . 9180253 . 9180253 . free .
  7. Li J, Huang CL, Zhang LW, Lin L, Li ZH, Zhang FW, Wang P . Isoforms of human O-GlcNAcase show distinct catalytic efficiencies . Biochemistry. Biokhimiia . 75 . 7 . 938–43 . July 2010 . 20673219 . 10.1134/S0006297910070175 . 2414800 .
  8. Web site: Greig. Ian. Vocadlo. David. Glycoside Hydrolase Family 84. Cazypedia. 28 March 2017.
  9. Gao Y, Wells L, Comer FI, Parker GJ, Hart GW . Dynamic O-glycosylation of nuclear and cytosolic proteins: cloning and characterization of a neutral, cytosolic beta-N-acetylglucosaminidase from human brain . The Journal of Biological Chemistry . 276 . 13 . 9838–45 . March 2001 . 11148210 . 10.1074/jbc.M010420200 . free .
  10. Lima VV, Rigsby CS, Hardy DM, Webb RC, Tostes RC . O-GlcNAcylation: a novel post-translational mechanism to alter vascular cellular signaling in health and disease: focus on hypertension . Journal of the American Society of Hypertension . 3 . 6 . 374–87 . 2009 . 20409980 . 3022480 . 10.1016/j.jash.2009.09.004 .
  11. Förster S, Welleford AS, Triplett JC, Sultana R, Schmitz B, Butterfield DA . Increased O-GlcNAc levels correlate with decreased O-GlcNAcase levels in Alzheimer disease brain . Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease . 1842 . 9 . 1333–9 . September 2014 . 24859566 . 4140188 . 10.1016/j.bbadis.2014.05.014 .
  12. Shafi R, Iyer SP, Ellies LG, O'Donnell N, Marek KW, Chui D, Hart GW, Marth JD . 6 . The O-GlcNAc transferase gene resides on the X chromosome and is essential for embryonic stem cell viability and mouse ontogeny . Proceedings of the National Academy of Sciences of the United States of America . 97 . 11 . 5735–9 . May 2000 . 10801981 . 18502 . 10.1073/pnas.100471497 . 2000PNAS...97.5735S . free .
  13. Love DC, Ghosh S, Mondoux MA, Fukushige T, Wang P, Wilson MA, Iser WB, Wolkow CA, Krause MW, Hanover JA . 6 . Dynamic O-GlcNAc cycling at promoters of Caenorhabditis elegans genes regulating longevity, stress, and immunity . Proceedings of the National Academy of Sciences of the United States of America . 107 . 16 . 7413–8 . April 2010 . 20368426 . 2867743 . 10.1073/pnas.0911857107 . 2010PNAS..107.7413L . free .
  14. Dennis RJ, Taylor EJ, Macauley MS, Stubbs KA, Turkenburg JP, Hart SJ, Black GN, Vocadlo DJ, Davies GJ . 6 . Structure and mechanism of a bacterial beta-glucosaminidase having O-GlcNAcase activity . Nature Structural & Molecular Biology . 13 . 4 . 365–71 . April 2006 . 16565725 . 10.1038/nsmb1079 . 9239755 .
  15. Alonso J, Schimpl M, van Aalten DM . O-GlcNAcase: promiscuous hexosaminidase or key regulator of O-GlcNAc signaling? . The Journal of Biological Chemistry . 289 . 50 . 34433–9 . December 2014 . 25336650 . 4263850 . 10.1074/jbc.R114.609198 . free .
  16. Lim S, Haque MM, Nam G, Ryoo N, Rhim H, Kim YK . Monitoring of Intracellular Tau Aggregation Regulated by OGA/OGT Inhibitors . International Journal of Molecular Sciences . 16 . 9 . 20212–24 . August 2015 . 26343633 . 4613198 . 10.3390/ijms160920212 . free .
  17. Roth C, Chan S, Offen WA, Hemsworth GR, Willems LI, King DT, Varghese V, Britton R, Vocadlo DJ, Davies GJ . 6 . Structural and functional insight into human O-GlcNAcase . Nature Chemical Biology . 13 . 6 . 610–612 . June 2017 . 28346405 . 5438047 . 10.1038/nchembio.2358 .

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