Uroporphyrinogen III decarboxylase is a homodimeric enzyme (PDB: 1URO) that catalyzes the fifth step in heme biosynthesis, which corresponds to the elimination of carboxyl groups from the four acetate side chains of uroporphyrinogen III to yield coproporphyrinogen III:
At low substrate concentrations, the reaction is believed to follow an ordered route, with the sequential removal of CO2 from the D, A, B, and C rings, whereas at higher substrate/enzyme levels a random route seems to be operative. The enzyme functions as a dimer in solution, and both the enzymes from human and tobacco have been crystallized and solved at good resolutions.
The reaction catalyzed by UroD
UroD is regarded as an unusual decarboxylase, since it performs decarboxylations without the intervention of any cofactors, unlike the vast majority of decarboxylases. Its mechanism has recently been proposed to proceed through substrate protonation by an arginine residue.[7] A 2008 report demonstrated that the uncatalyzed rate for UroD's reaction is 10−19 s−1, so at pH 10 the rate acceleration of UroD relative to the uncatalyzed rate, i.e. catalytic proficiency, is the largest for any enzyme known, 6 x 1024 M−1.[8]
Proposed reaction mechanism of uroporphyrinogen III decarboxylase
^Silva PJ, Ramos MJ (2005). "Density-functional study of mechanisms for the cofactor-free decarboxylation performed by uroporphyrinogen III decarboxylase". J Phys Chem B. 109 (38): 18195–200. doi:10.1021/jp051792s. PMID16853337.
Elder GH, Lee GB, Tovey JA (1978). "Decreased activity of hepatic uroporphyrinogen decarboxylase in sporadic porphyria cutanea tarda". N. Engl. J. Med. 299 (6): 274–8. doi:10.1056/NEJM197808102990603. PMID661926.
Romana M, Grandchamp B, Dubart A, et al. (1991). "Identification of a new mutation responsible for hepatoerythropoietic porphyria". Eur. J. Clin. Invest. 21 (2): 225–9. doi:10.1111/j.1365-2362.1991.tb01814.x. PMID1905636. S2CID22358220.
Dubart A, Mattei MG, Raich N, et al. (1986). "Assignment of human uroporphyrinogen decarboxylase (URO-D) to the p34 band of chromosome 1". Hum. Genet. 73 (3): 277–9. doi:10.1007/BF00401245. PMID3460962. S2CID34478515.
de Verneuil H, Grandchamp B, Beaumont C, et al. (1986). "Uroporphyrinogen decarboxylase structural mutant (Gly281----Glu) in a case of porphyria". Science. 234 (4777): 732–4. Bibcode:1986Sci...234..732D. doi:10.1126/science.3775362. PMID3775362.
Maruyama K, Sugano S (1994). "Oligo-capping: a simple method to replace the cap structure of eukaryotic mRNAs with oligoribonucleotides". Gene. 138 (1–2): 171–4. doi:10.1016/0378-1119(94)90802-8. PMID8125298.
Meguro K, Fujita H, Ishida N, et al. (1994). "Molecular defects of uroporphyrinogen decarboxylase in a patient with mild hepatoerythropoietic porphyria". J. Invest. Dermatol. 102 (5): 681–5. doi:10.1111/1523-1747.ep12374134. PMID8176248.
Suzuki Y, Yoshitomo-Nakagawa K, Maruyama K, et al. (1997). "Construction and characterization of a full length-enriched and a 5'-end-enriched cDNA library". Gene. 200 (1–2): 149–56. doi:10.1016/S0378-1119(97)00411-3. PMID9373149.
Wang H, Long Q, Marty SD, et al. (1998). "A zebrafish model for hepatoerythropoietic porphyria". Nat. Genet. 20 (3): 239–43. doi:10.1038/3041. PMID9806541. S2CID28379777.
Christiansen L, Ged C, Hombrados I, et al. (1999). "Screening for mutations in the uroporphyrinogen decarboxylase gene using denaturing gradient gel electrophoresis. Identification and characterization of six novel mutations associated with familial PCT". Hum. Mutat. 14 (3): 222–32. doi:10.1002/(SICI)1098-1004(1999)14:3<222::AID-HUMU5>3.0.CO;2-V. PMID10477430.
External links[]
Overview of all the structural information available in the PDB for UniProt: P06132 (Uroporphyrinogen decarboxylase) at the PDBe-KB.
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PDB gallery
1jph: Ile260Thr mutant of Human UroD, human uroporphyrinogen III decarboxylase
1jpi: Phe232Leu mutant of human UROD, human uroporphyrinogen III decarboxylase
1jpk: Gly156Asp mutant of Human UroD, human uroporphyrinogen III decarboxylase
1r3q: Uroporphyrinogen Decarboxylase in complex with coproporphyrinogen-I
1r3r: Uroporphyrinogen Decarboxylase with mutation D86N
1r3s: Uroporphyrinogen Decarboxylase single mutant D86G in complex with coproporphyrinogen-I
1r3t: Uroporphyrinogen Decarboxylase single mutant D86G in complex with coproporphyrinogen-III
1r3v: Uroporphyrinogen Decarboxylase single mutant D86E in complex with coproporphyrinogen-I
1r3w: Uroporphyrinogen Decarboxylase Y164F mutant in complex with coproporphyrinogen-III
1r3y: Uroporphyrinogen Decarboxylase in complex with coproporphyrinogen-III
1uro: UROPORPHYRINOGEN DECARBOXYLASE
Heme synthesis—note that some reactions occur in the cytoplasm and some in the mitochondrion (yellow)