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Hunter GA, Al-Karadaghi S, Ferreira GC. FERROCHELATASE: THE CONVERGENCE OF THE PORPHYRIN BIOSYNTHESIS AND IRON TRANSPORT PATHWAYS. J PORPHYR PHTHALOCYA 2012; 15:350-356. [PMID: 21852895 DOI: 10.1142/s108842461100332x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Ferrochelatase (also known as PPIX ferrochelatase; Enzyme Commission number 4.9.9.1.1) catalyzes the insertion of ferrous iron into PPIX to form heme. This reaction unites the biochemically synchronized pathways of porphyrin synthesis and iron transport in nearly all living organisms. The ferrochelatases are an evolutionarily diverse family of enzymes with no more than six active site residues known to be perfectly conserved. The availability of over thirty different crystal structures, including many with bound metal ions or porphyrins, has added tremendously to our understanding of ferrochelatase structure and function. It is generally believed that ferrous iron is directly channeled to ferrochelatase in vivo, but the identity of the suspected chaperone remains uncertain despite much recent progress in this area. Identification of a conserved metal ion binding site at the base of the active site cleft may be an important clue as to how ferrochelatases acquire iron, and catalyze desolvation during transport to the catalytic site to complete heme synthesis.
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Affiliation(s)
- Gregory A Hunter
- Department of Molecular Medicine, College of Medicine, University of South Florida, Tampa, Florida, 33620
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The C-terminal extension of ferrochelatase is critical for enzyme activity and for functioning of the tetrapyrrole pathway in Synechocystis strain PCC 6803. J Bacteriol 2008; 190:2086-95. [PMID: 18192382 DOI: 10.1128/jb.01678-07] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Heme and chlorophyll (Chl) share a common biosynthetic pathway up to the branch point where magnesium chelatase and ferrochelatase (FeCH) insert either magnesium for Chl biosynthesis or ferrous iron for heme biosynthesis. A distinctive feature of FeCHs in cyanobacteria is their C-terminal extension, which forms a putative transmembrane segment containing a Chl-binding motif. We analyzed the deltaH324 strain of Synechocystis sp. strain PCC 6803, which contains a truncated FeCH enzyme lacking this C-terminal domain. Truncated FeCH was localized to the membrane fraction, suggesting that the C-terminal domain is not necessary for membrane association of the enzyme. Measurements of enzyme activity and complementation experiments revealed that the deltaH324 mutation dramatically reduced activity of the FeCH, which resulted in highly upregulated 5-aminolevulinic acid synthesis in the deltaH324 mutant, implying a direct role for heme in the regulation of flux through the pathway. Moreover, the deltaH324 mutant accumulated a large amount of protoporphyrin IX, and levels of Chl precursors were also significantly increased, suggesting that some, but not all, of the "extra" flux can be diverted down the Chl branch. Analysis of the recombinant full-length and truncated FeCHs demonstrated that the C-terminal extension is critical for activity of the FeCH and that it is strictly required for oligomerization of this enzyme. The observed changes in tetrapyrrole trafficking and the role of the C terminus in the functioning of FeCH are discussed.
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Dailey T, Woodruff J, Dailey H. Examination of mitochondrial protein targeting of haem synthetic enzymes: in vivo identification of three functional haem-responsive motifs in 5-aminolaevulinate synthase. Biochem J 2005; 386:381-6. [PMID: 15482256 PMCID: PMC1134803 DOI: 10.1042/bj20040570] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The initial and the terminal three enzymes of the mammalian haem biosynthetic pathway are nuclear encoded, cytoplasmically synthesized and post-translationally translocated into the mitochondrion. The first enzyme, ALAS (5-aminolaevulinate synthase), occurs as an isoenzyme encoded on different chromosomes and is synthesized either as a housekeeping protein (ALAS-1) in all non-erythroid cell types, or only in differentiating erythroid precursor cells (ALAS-2). Both ALAS proteins possess mitochondrial targeting sequences that have putative haem-binding motifs. In the present study, evidence is presented demonstrating that two haem-binding motifs in the leader sequence, as well as one present in the N-terminus of the mature ALAS-1 function in vivo in the haem-regulated translocation of ALAS-1. Coproporphyrinogen oxidase, the antepenultimate pathway enzyme, possesses a leader sequence that is approx. 120 residues long. In contrast with an earlier report suggesting that only 30 residues were required for translocation of the coproporphyrinogen oxidase, we report that the complete leader is necessary for translocation and that this process is not haem-sensitive in vivo. PPO (protoporphyrinogen oxidase) lacks a typical mitochondrial targeting leader sequence and was found to be effectively targeted by just 17 N-terminal residues. Bacillus subtilis PPO, which is very similar to human PPO at its N-terminal end, is not targeted to the mitochondrion when expressed in mammalian cells, demonstrating that the translocation is highly specific with regard to both the length and spacing of charged residues in this targeting region. Ferrochelatase, the terminal enzyme, possesses a typical N-terminal leader sequence and no evidence of a role for the C-terminus was found in mitochondrial targeting.
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Affiliation(s)
- Tamara A. Dailey
- Departments of Microbiology, Biochemistry and Molecular Biology, Biomedical and Health Sciences Institute, University of Georgia, Athens, GA 30602-7229, U.S.A
| | - John H. Woodruff
- Departments of Microbiology, Biochemistry and Molecular Biology, Biomedical and Health Sciences Institute, University of Georgia, Athens, GA 30602-7229, U.S.A
| | - Harry A. Dailey
- Departments of Microbiology, Biochemistry and Molecular Biology, Biomedical and Health Sciences Institute, University of Georgia, Athens, GA 30602-7229, U.S.A
- To whom correspondence should be addressed (email )
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Franco R, Bai G, Prosinecki V, Abrunhosa F, Ferreira G, Bastos M. Porphyrin-substrate binding to murine ferrochelatase: effect on the thermal stability of the enzyme. Biochem J 2005; 386:599-605. [PMID: 15496139 PMCID: PMC1134880 DOI: 10.1042/bj20040921] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2004] [Revised: 10/07/2004] [Accepted: 10/21/2004] [Indexed: 11/17/2022]
Abstract
Ferrochelatase (EC 4.99.1.1), the terminal enzyme of the haem biosynthetic pathway, catalyses the chelation of Fe(II) into the protoporphyrin IX ring. The energetics of the binding between murine ferrochelatase and mesoporphyrin were determined using isothermal titration calorimetry, which revealed a stoichiometry of one molecule of mesoporphyrin bound per protein monomer. The binding is strongly exothermic, with a large intrinsic enthalpy (DeltaH=-97.1 kJ x mol(-1)), and is associated with the uptake of two protons from the buffer. This proton transfer suggests that hydrogen bonding between ferrochelatase and mesoporphyrin is a key factor in the thermodynamics of the binding reaction. Differential scanning calorimetry thermograms indicated a co-operative two-state denaturation process with a single transition temperature of 56 degrees C for wild-type murine ferrochelatase. An increase in the thermal stability of ferrochelatase is dependent upon mesoporphyrin binding. Similarly, murine ferrochelatase variants, in which the active site Glu-289 was replaced by either glutamine or alanine and, when purified, contained specifically-bound protoporphyrin, exhibited enhanced protein stability when compared with wild-type ferrochelatase. However, in contrast with the wild-type enzyme, the thermal denaturation of ferrochelatase variants was best described as a non-co-operative denaturation process.
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Affiliation(s)
- Ricardo Franco
- *Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Apartado 127, 2781-901 Oeiras, Portugal
| | - Guangyue Bai
- †CIQ(UP), Departamento de Química, Faculdade de Ciências da Universidade do Porto, R. Campo Alegre 687, 4169-007 Porto, Portugal
| | - Vesna Prosinecki
- *Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Apartado 127, 2781-901 Oeiras, Portugal
| | - Filipa Abrunhosa
- †CIQ(UP), Departamento de Química, Faculdade de Ciências da Universidade do Porto, R. Campo Alegre 687, 4169-007 Porto, Portugal
| | - Gloria C. Ferreira
- ‡Department of Biochemistry and Molecular Biology, College of Medicine, University of South Florida, Tampa, FL 33612, U.S.A
- §H. Lee Moffitt Cancer Center and Research Institute, University of South Florida, Tampa, FL 33612, U.S.A
| | - Margarida Bastos
- †CIQ(UP), Departamento de Química, Faculdade de Ciências da Universidade do Porto, R. Campo Alegre 687, 4169-007 Porto, Portugal
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O'Brian MR, Thöny-Meyer L. Biochemistry, regulation and genomics of haem biosynthesis in prokaryotes. Adv Microb Physiol 2002; 46:257-318. [PMID: 12073655 DOI: 10.1016/s0065-2911(02)46006-7] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Haems are involved in many cellular processes in prokaryotes and eukaryotes. The biosynthetic pathway leading to haem formation is, with few exceptions, well-conserved, and is controlled in accordance with cellular function. Here, we review the biosynthesis of haem and its regulation in prokaryotes. In addition, we focus on a modification of haem for cytochrome c biogenesis, a complex process that entails both transport between cellular compartments and a specific thioether linkage between the haem moiety and the apoprotein. Finally, a whole genome analysis from 63 prokaryotes indicates intriguing exceptions to the universality of the haem biosynthetic pathway and helps define new frontiers for future study.
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Affiliation(s)
- Mark R O'Brian
- Department of Biochemistry, State University of New York at Buffalo, Buffalo, NY 14214, USA
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Grzybowska E, Góra M, Plochocka D, Rytka J. Saccharomyces cerevisiae ferrochelatase forms a homodimer. Arch Biochem Biophys 2002; 398:170-8. [PMID: 11831847 DOI: 10.1006/abbi.2001.2730] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ferrochelatase, the last enzyme of the heme biosynthetic pathway, has for years been considered to be active as a monomer. The crystal structure of Bacillus subtilis ferrochelatase confirmed its monomeric structure. However, animal ferrochelatase was found to form a functional dimer. Data presented here indicate that ferrochelatase from the yeast Saccharomyces cerevisiae is also dimeric. Following two-hybrid studies that had shown an interaction of two ferrochelatase molecules, we employed several different, complementary approaches, such as chemical crosslinking, affinity chromatography, and complementation analysis, to prove that in the yeast cells ferrochelatase forms an active dimer. We have isolated a double mutant, hem15D246V/Y248F, which is probably dimerization-defective. We propose a structural model of yeast ferrochelatase, based on the known structure of the human enzyme, which helps us to understand the differences in dimerization between the wild-type and mutant proteins.
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Affiliation(s)
- Ewa Grzybowska
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5A, Warsaw, 02-106, Poland
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Wang KF, Dailey TA, Dailey HA. Expression and characterization of the terminal heme synthetic enzymes from the hyperthermophile Aquifex aeolicus. FEMS Microbiol Lett 2001; 202:115-9. [PMID: 11506917 DOI: 10.1111/j.1574-6968.2001.tb10789.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
The terminal two heme biosynthetic pathway enzymes, protoporphyrinogen oxidase and ferrochelatase, of the hyperthermophilic bacterium Aquifex aeolicus have been expressed in Escherichia coli, purified to homogeneity, and biochemically characterized. Ferrochelatase and protoporphyrinogen oxidase of this organism are both monomeric, as was found for the corresponding enzymes of Bacillus subtilis. However, unlike the B. subtilis proteins, both A. aeolicus enzymes are membrane-associated. Both proteins have temperature optima over 60 degrees C. This is the first demonstration of functional heme biosynthetic enzymes in an extreme thermophilic bacterium.
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Affiliation(s)
- K F Wang
- Department of Microbiology, University of Georgia, Athens, GA 30602-7229, USA
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Abstract
Ferrochelatase with an Mr of 42,700 Da and a pI of 7.35 has been purified to homogeneity from chironomidae larvae. The activity of the enzyme reached maximum at pH 7.8 and decreased with the increase of pH. The enzyme activity varied with temperature and showed maximum activity around 37 degrees C. The purified enzyme was active towards protoporphyrin but inactive towards other porphyrins. The specific enzyme activity of ferrochelatase from chironomidae is about 10-fold higher than that of the rat. Electrophoresis of the purified fractions shows that the enzyme contains only one single polypeptide. The soluble ferrochelatase contained one mole of iron in each mole of the enzyme. The N-terminal sequence analysis of the enzyme shows a high percentage of conserved regions of the enzyme among other species. The enzyme properties are similar to those of the mammalian ferrochelatases except with slightly higher specific activity. Chironomidae ferrochelatase appeared to be more heat resistant and less susceptible than its mammalian equivalent to inhibition by lead.
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Affiliation(s)
- Y K Leung
- Department of Biochemistry, The Chinese University of Hong Kong, Shatin
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Ni L, Zhou J, Hurley TD, Weiner H. Human liver mitochondrial aldehyde dehydrogenase: three-dimensional structure and the restoration of solubility and activity of chimeric forms. Protein Sci 1999; 8:2784-90. [PMID: 10631996 PMCID: PMC2144226 DOI: 10.1110/ps.8.12.2784] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Human liver cytosolic and mitochondrial isozymes of aldehyde dehydrogenase share 70% sequence identity. However, the first 21 residues are not conserved between the human isozymes (15% identity). The three-dimensional structures of the beef mitochondrial and sheep cytosolic forms have virtually identical three-dimensional structures. Here, we solved the structure of the human mitochondrial enzyme and found it to be identical to the beef enzyme. The first 21 residues are found on the surface of the enzyme and make no contact with other subunits in the tetramer. A pair of chimeric enzymes between the human isozymes was made. Each chimera had the first 21 residues from one isozyme and the remaining 479 from the other. When the first 21 residues were from the mitochondrial isozyme, an enzyme with cytosolic-like properties was produced. The other was expressed but was insoluble. It was possible to restore solubility and activity to the chimera that had the first 21 cytosolic residues fused to the mitochondrial ones by making point mutations to residues at the N-terminal end. When residue 19 was changed from tyrosine to a cysteine, the residue found in the mitochondrial form, an active enzyme could be made though the Km for NAD+ was 35 times higher than the native mitochondrial isozyme and the specific activity was reduced by 75%. This residue interacts with residue 203, a nonconserved, nonactive site residue. A mutation of residue 18, which also interacts with 203, restored solubility, but not activity. Mutation to residue 15, which interacts with 104, also restored solubility but not activity. It appears that to have a soluble or active enzyme a favorable interaction must occur between a residue in a surface loop and a residue elsewhere in the molecule even though neither make contact with the active site region of the enzyme.
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Affiliation(s)
- L Ni
- Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907-1153, USA
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