Biology:Hypoxanthine-guanine phosphoribosyltransferase

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Short description: Enzyme that converts hypoxanthine to inosine monophosphate


A representation of the 3D structure of the protein myoglobin showing turquoise α-helices.
Generic protein structure example

Hypoxanthine-guanine phosphoribosyltransferase (HGPRT) is an enzyme encoded in humans by the HPRT1 gene.[1][2]

HGPRT is a transferase that catalyzes conversion of hypoxanthine to inosine monophosphate and guanine to guanosine monophosphate. This reaction transfers the 5-phosphoribosyl group from 5-phosphoribosyl 1-pyrophosphate (PRPP) to the purine. HGPRT plays a central role in the generation of purine nucleotides through the purine salvage pathway.

Function

hypoxanthine phosphoribosyltransferase
Identifiers
EC number2.4.2.8
CAS number9016-12-0
Databases
IntEnzIntEnz view
BRENDABRENDA entry
ExPASyNiceZyme view
KEGGKEGG entry
MetaCycmetabolic pathway
PRIAMprofile
PDB structuresRCSB PDB PDBe PDBsum
Gene OntologyAmiGO / QuickGO

HGPRT catalyzes the following reactions:

Substrate Product Notes
hypoxanthine inosine monophosphate —
guanine guanosine monophosphate Often called HGPRT. Performs this function only in some species.
xanthine xanthosine monophosphate Only certain HPRTs.

HGPRTase functions primarily to salvage purines from degraded DNA to reintroduce into purine synthetic pathways. In this role, it catalyzes the reaction between guanine and phosphoribosyl pyrophosphate (PRPP) to form GMP, or between hypoxanthine and phosphoribosyl pyrophosphate (PRPP) to form inosine monophosphate.

Substrates and inhibitors

Comparative homology modelling of this enzyme in L. donovani suggest that among all of the computationally screened compounds, pentamidine, 1,3-dinitroadamantane, acyclovir and analogs of acyclovir had higher binding affinities than the real substrate (guanosine monophosphate).[3] The in silico and in-vitro correlation of these compounds were test in Leishmania HGPRT and validates the result.[4]

Role in disease

Mutations in the gene lead to hyperuricemia. At least 67 disease-causing mutations in this gene have been discovered:[5]

  • Some men have partial (up to 20% less activity of the enzyme) HGPRT deficiency that causes high levels of uric acid in the blood, which leads to the development of gouty arthritis and the formation of uric acid stones in the urinary tract. This condition has been named the Kelley–Seegmiller syndrome.[6]
  • Lesch–Nyhan syndrome is due to deficiency of HGPRT caused by HPRT1 mutation.[7]
  • Some mutations have been linked to gout, the risk of which is increased in hypoxanthine-guanine phosphoribosyltransferase deficiency.
  • HPRT expression on the mRNA and protein level is induced by hypoxia inducible factor 1 (HIF1A). HIF-1 is a transcription factor that directs an array of cellular responses that are used for adaptation during oxygen deprivation. This finding implies that HPRT is a critical pathway that helps preserve the cell's purine nucleotide resources under hypoxic conditions as found in pathology such as myocardial ischemia.[8]

Creation of hybridomas

Hybridomas are immortal (immune to cellular senescence), HGPRT+ cells that result from fusion of mortal, HGPRT+ plasma cells and immortal, HGPRT− myeloma cells. They are created to produce monoclonal antibodies in biotechnology. HAT medium inhibits de novo synthesis of nucleic acids, killing myeloma cells that cannot switch over to the salvage pathway, due to lack of HPRT1. The plasma cells in the culture eventually die from senescence, leaving pure hybridoma cells.

References

  1. ↑ "Entrez Gene: hypoxanthine phosphoribosyltransferase 1 (Lesch-Nyhan syndrome)". https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=gene&cmd=retrieve&dopt=default&list_uids=3251&rn=1. 
  2. ↑ "Mutational spectral analysis at the HPRT locus in healthy children". Mutation Research 505 (1–2): 27–41. Aug 2002. doi:10.1016/S0027-5107(02)00119-7. PMID 12175903. 
  3. ↑ "Comparative modeling of HGPRT enzyme of L. donovani and binding affinities of different analogs of GMP". International Journal of Biological Macromolecules 50 (3): 637–49. Apr 2012. doi:10.1016/j.ijbiomac.2012.01.010. PMID 22327112. 
  4. ↑ "Establishment of Correlation between In-Silico &In-Vitro Test Analysis against Leishmania HGPRT to inhibitors". International Journal of Biological Macromolecules 83: 78–96. Nov 2015. doi:10.1016/j.ijbiomac.2015.11.051. PMID 26616453. 
  5. ↑ "Refinement of evolutionary medicine predictions based on clinical evidence for the manifestations of Mendelian diseases". Scientific Reports 9 (1): 18577. December 2019. doi:10.1038/s41598-019-54976-4. PMID 31819097. Bibcode: 2019NatSR...918577S. 
  6. ↑ "Kelley-Seegmiller syndrome: a case report and review of the literature". British Journal of Rheumatology 37 (5): 580–1. May 1998. doi:10.1093/rheumatology/37.5.580c. PMID 9651092. 
  7. ↑ "Variable expression of HPRT deficiency in 5 members of a family with the same mutation". Archives of Neurology 65 (9): 1240–3. Sep 2008. doi:10.1001/archneur.65.9.1240. PMID 18779430. 
  8. ↑ "HIF-1α in the heart: Remodeling nucleotide metabolism". Journal of Molecular and Cellular Cardiology 82: 194–200. Feb 2015. doi:10.1016/j.yjmcc.2015.01.014. PMID 25681585. 

Further reading

External links



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