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Hatalová T, Erhart J, Kopáček P, Perner J. On the haem auxotrophy of the soft tick Ornithodoros moubata. Ticks Tick Borne Dis 2023; 14:102170. [PMID: 36958097 DOI: 10.1016/j.ttbdis.2023.102170] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2022] [Revised: 03/14/2023] [Accepted: 03/15/2023] [Indexed: 03/25/2023]
Abstract
Genomes of ticks display reductions, to various extents, in genetic coding for enzymes of the haem biosynthetic pathway. Here, we mined available transcriptomes of soft tick species and identified transcripts encoding only half of the enzymes involved in haem biosynthesis. Transcripts identified across most species examined were those coding for porphobilinogen synthase, coproporphyrinogen oxidase, protoporphyrinogen oxidase, and ferrochelatase. Genomic retention of porphobilinogen synthase seems to be soft tick-restricted as no such homologue has been identified in any hard tick species. Bioinformatic mining is thus strongly indicative of the lack of biochemical capacity for de novo haem biosynthesis, suggesting a requirement for dietary haem. In the hard tick Ixodes ricinus, depletion of dietary haem, i.e. serum feeding, leads to oviposition of haem-free eggs, with no apparent embryogenesis and larvae formation. In this work, we show that serum-fed Ornithodoros moubata females, unlike those of I. ricinus, laid haem-containing eggs similarly to blood-fed controls, but only by a small proportion of the serum-fed females. To enhance the effect of dietary haem depletion, O. moubata ticks were serum-fed consecutively as last nymphal instars and females. These females laid eggs with profoundly reduced haem deposits, confirming the host origin of the haem. These data confirm the ability of soft ticks to take up and allocate host haem to their eggs in order to drive reproduction of the ticks.
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Affiliation(s)
- Tereza Hatalová
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Ceske Budejovice 37005, Czech Republic; Faculty of Science, University of South Bohemia, Ceske Budejovice, Czech Republic
| | - Jan Erhart
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Ceske Budejovice 37005, Czech Republic
| | - Petr Kopáček
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Ceske Budejovice 37005, Czech Republic
| | - Jan Perner
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Ceske Budejovice 37005, Czech Republic.
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2
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Liu G, Sil D, Maio N, Tong WH, Bollinger JM, Krebs C, Rouault TA. Heme biosynthesis depends on previously unrecognized acquisition of iron-sulfur cofactors in human amino-levulinic acid dehydratase. Nat Commun 2020; 11:6310. [PMID: 33298951 PMCID: PMC7725820 DOI: 10.1038/s41467-020-20145-9] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2020] [Accepted: 11/06/2020] [Indexed: 12/18/2022] Open
Abstract
Heme biosynthesis and iron-sulfur cluster (ISC) biogenesis are two major mammalian metabolic pathways that require iron. It has long been known that these two pathways interconnect, but the previously described interactions do not fully explain why heme biosynthesis depends on intact ISC biogenesis. Herein we identify a previously unrecognized connection between these two pathways through our discovery that human aminolevulinic acid dehydratase (ALAD), which catalyzes the second step of heme biosynthesis, is an Fe-S protein. We find that several highly conserved cysteines and an Ala306-Phe307-Arg308 motif of human ALAD are important for [Fe4S4] cluster acquisition and coordination. The enzymatic activity of human ALAD is greatly reduced upon loss of its Fe-S cluster, which results in reduced heme biosynthesis in human cells. As ALAD provides an early Fe-S-dependent checkpoint in the heme biosynthetic pathway, our findings help explain why heme biosynthesis depends on intact ISC biogenesis. Heme biosynthesis depends on iron-sulfur (Fe-S) cluster biogenesis but the molecular connection between these pathways is not fully understood. Here, the authors show that the heme biosynthesis enzyme ALAD contains an Fe-S cluster, disruption of which reduces ALAD activity and heme production in human cells.
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Affiliation(s)
- Gang Liu
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Debangsu Sil
- Department of Chemistry, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Nunziata Maio
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Wing-Hang Tong
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - J Martin Bollinger
- Department of Chemistry, The Pennsylvania State University, University Park, PA, 16802, USA.,Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Carsten Krebs
- Department of Chemistry, The Pennsylvania State University, University Park, PA, 16802, USA. .,Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, 16802, USA.
| | - Tracey Ann Rouault
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA.
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3
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Porphobilinogen synthase: An equilibrium of different assemblies in human health. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2019; 169:85-104. [PMID: 31952692 DOI: 10.1016/bs.pmbts.2019.11.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Porphobilinogen synthase (PBGS) is an essential enzyme that catalyzes an early step in heme biosynthesis. An unexpected human PBGS quaternary structure dynamic drove the definition of morpheeins, which are protein multimers that dissociate, change shape, and re-assemble differently with functional consequences. Each PBGS monomer has two domains that can reposition through a hinge motion. Human PBGS exists in an equilibrium among high activity octamer, low activity hexamer, and low mole-fraction dimer in which the hinge motion occurs. The dimer conformation dictates the multimer architecture. An octamer-specific inter-subunit interaction responds to pH, resulting in a pH-dependence to the octamer-hexamer equilibrium. An inborn error of metabolism, ALAD porphyria, is caused by single amino acid substitutions that stabilize the hexamer relative to octamer. Drugs that stabilize the PBGS hexamer result in a drug side effect that can exacerbate porphyria. PBGS is essential for all organisms that require respiration, photosynthesis, or methanogenesis. Consequently, phylogenetic variation in PBGS multimerization equilibria provides insight into how Nature has harnessed oligomeric variation in the control of protein function. The dynamic multimerization of PBGS revealed the morpheein mechanism for allostery, a structural basis for inborn errors of metabolism, a quaternary structure focus for drug discovery and/or drug side effects, and a pathway toward new antibiotics or herbicides. The fortuitous discovery of PBGS quaternary structure dynamics arose from characterization of a low-activity single amino acid variant that dramatically stabilized the hexamer, whose existence had previously gone unnoticed.
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4
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Lin CI, McCarty RM, Liu HW. The Enzymology of Organic Transformations: A Survey of Name Reactions in Biological Systems. Angew Chem Int Ed Engl 2017; 56:3446-3489. [PMID: 27505692 PMCID: PMC5477795 DOI: 10.1002/anie.201603291] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2016] [Indexed: 01/05/2023]
Abstract
Chemical reactions that are named in honor of their true, or at least perceived, discoverers are known as "name reactions". This Review is a collection of biological representatives of named chemical reactions. Emphasis is placed on reaction types and catalytic mechanisms that showcase both the chemical diversity in natural product biosynthesis as well as the parallels with synthetic organic chemistry. An attempt has been made, whenever possible, to describe the enzymatic mechanisms of catalysis within the context of their synthetic counterparts and to discuss the mechanistic hypotheses for those reactions that are currently active areas of investigation. This Review has been categorized by reaction type, for example condensation, nucleophilic addition, reduction and oxidation, substitution, carboxylation, radical-mediated, and rearrangements, which are subdivided by name reactions.
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Affiliation(s)
- Chia-I Lin
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, and Department of Chemistry, University of Texas at Austin, Austin, TX, 78731, USA
| | - Reid M McCarty
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, and Department of Chemistry, University of Texas at Austin, Austin, TX, 78731, USA
| | - Hung-Wen Liu
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, and Department of Chemistry, University of Texas at Austin, Austin, TX, 78731, USA
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5
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Lin C, McCarty RM, Liu H. Die Enzymologie organischer Umwandlungen: Namensreaktionen in biologischen Systemen. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201603291] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Chia‐I. Lin
- Division of Chemical Biology and Medicinal Chemistry College of Pharmacy, and Department of Chemistry University of Texas at Austin Austin TX 78731 USA
| | - Reid M. McCarty
- Division of Chemical Biology and Medicinal Chemistry College of Pharmacy, and Department of Chemistry University of Texas at Austin Austin TX 78731 USA
| | - Hung‐wen Liu
- Division of Chemical Biology and Medicinal Chemistry College of Pharmacy, and Department of Chemistry University of Texas at Austin Austin TX 78731 USA
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6
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Liberato A, Aguinaco A, Clares MP, Delgado-Pinar E, Pitarch-Jarque J, Blasco S, Basallote MG, García-España E, Verdejo B. Pb2+ complexes of small-cavity azamacrocyclic ligands: thermodynamic and kinetic studies. Dalton Trans 2017; 46:6645-6653. [DOI: 10.1039/c7dt00680b] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The synthesis and Pb2+ coordination of azamacrocyclic ligands have been described. This paper includes one of the few kinetic studies so far reported on the acid-promoted dissociation of Pb2+ macrocyclic complexes.
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Affiliation(s)
- A. Liberato
- Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica
- Facultad de Ciencias
- Universidad de Cádiz
- Puerto Real
- Spain
| | - A. Aguinaco
- Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica
- Facultad de Ciencias
- Universidad de Cádiz
- Puerto Real
- Spain
| | - M. P. Clares
- Instituto de Ciencia Molecular
- Departamento de Química Inorgánica
- Universidad de Valencia
- Edificio de Institutos de Paterna
- Paterna
| | - E. Delgado-Pinar
- Instituto de Ciencia Molecular
- Departamento de Química Inorgánica
- Universidad de Valencia
- Edificio de Institutos de Paterna
- Paterna
| | - J. Pitarch-Jarque
- Instituto de Ciencia Molecular
- Departamento de Química Inorgánica
- Universidad de Valencia
- Edificio de Institutos de Paterna
- Paterna
| | - S. Blasco
- Instituto de Ciencia Molecular
- Departamento de Química Inorgánica
- Universidad de Valencia
- Edificio de Institutos de Paterna
- Paterna
| | - M. G. Basallote
- Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica
- Facultad de Ciencias
- Universidad de Cádiz
- Puerto Real
- Spain
| | - E. García-España
- Instituto de Ciencia Molecular
- Departamento de Química Inorgánica
- Universidad de Valencia
- Edificio de Institutos de Paterna
- Paterna
| | - B. Verdejo
- Instituto de Ciencia Molecular
- Departamento de Química Inorgánica
- Universidad de Valencia
- Edificio de Institutos de Paterna
- Paterna
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7
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Mills-Davies N, Butler D, Norton E, Thompson D, Sarwar M, Guo J, Gill R, Azim N, Coker A, Wood SP, Erskine PT, Coates L, Cooper JB, Rashid N, Akhtar M, Shoolingin-Jordan PM. Structural studies of substrate and product complexes of 5-aminolaevulinic acid dehydratase from humans,Escherichia coliand the hyperthermophilePyrobaculum calidifontis. ACTA CRYSTALLOGRAPHICA SECTION D-STRUCTURAL BIOLOGY 2017; 73:9-21. [DOI: 10.1107/s2059798316019525] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2016] [Accepted: 12/06/2016] [Indexed: 11/11/2022]
Abstract
A number of X-ray analyses of an enzyme involved in a key early stage of tetrapyrrole biosynthesis are reported. Two structures of human 5-aminolaevulinate dehydratase (ALAD), native and recombinant, have been determined at 2.8 Å resolution, showing that the enzyme adopts an octameric quaternary structure in accord with previously published analyses of the enzyme from a range of other species. However, this is in contrast to the finding that a disease-related F12L mutant of the human enzyme uniquely forms hexamers [Breiniget al.(2003),Nature Struct. Biol.10, 757–763]. Monomers of all ALADs adopt the TIM-barrel fold; the subunit conformation that assembles into the octamer includes the N-terminal tail of one monomer curled around the (α/β)8barrel of a neighbouring monomer. Both crystal forms of the human enzyme possess two monomers per asymmetric unit, termedAandB. In the native enzyme there are a number of distinct structural differences between theAandBmonomers, with the latter exhibiting greater disorder in a number of loop regions and in the active site. In contrast, the second monomer of the recombinant enzyme appears to be better defined and the active site of both monomers clearly possesses a zinc ion which is bound by three conserved cysteine residues. In native human ALAD, theAmonomer also has a ligand resembling the substrate ALA which is covalently bound by a Schiff base to one of the active-site lysines (Lys252) and is held in place by an ordered active-site loop. In contrast, these features of the active-site structure are disordered or absent in theBsubunit of the native human enzyme. The octameric structure of the zinc-dependent ALAD from the hyperthermophilePyrobaculum calidifontisis also reported at a somewhat lower resolution of 3.5 Å. Finally, the details are presented of a high-resolution structure of theEscherichia coliALAD enzyme co-crystallized with a noncovalently bound moiety of the product, porphobilinogen (PBG). This structure reveals that the pyrrole side-chain amino group is datively bound to the active-site zinc ion and that the PBG carboxylates interact with the enzymeviahydrogen bonds and salt bridges with invariant residues. A number of hydrogen-bond interactions that were previously observed in the structure of yeast ALAD with a cyclic intermediate resembling the product PBG appear to be weaker in the new structure, suggesting that these interactions are only optimal in the transition state.
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8
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Abstract
Porphobilinogen synthase (PBGS), also known as 5-aminolevulinate dehydratase, is an essential enzyme in the biosynthesis of all tetrapyrroles, which function in respiration, photosynthesis, and methanogenesis. Throughout evolution, PBGS adapted to a diversity of cellular niches and evolved to use an unusual variety of metal ions both for catalytic function and to control protein multimerization. With regard to the active site, some PBGSs require Zn2+; a subset of those, including human PBGS, contain a constellation of cysteine residues that acts as a sink for the environmental toxin Pb2+. PBGSs that do not require the soft metal ion Zn2+ at the active site instead are suspected of using the hard metal Mg2+. The most unexpected property of the PBGS family of enzymes is a dissociative allosteric mechanism that utilizes an equilibrium of architecturally and functionally distinct protein assemblies. The high-activity assembly is an octamer in which intersubunit interactions modulate active-site lid motion. This octamer can dissociate to dimer, the dimer can undergo a hinge twist, and the twisted dimer can assemble to a low-activity hexamer. The hexamer does not have the intersubunit interactions required to stabilize a closed conformation of the active site lid. PBGS active site chemistry benefits from a closed lid because porphobilinogen biosynthesis includes Schiff base formation, which requires deprotonated lysine amino groups. N-terminal and C-terminal sequence extensions dictate whether a specific species of PBGS can sample the hexameric assembly. The bulk of species (nearly all except animals and yeasts) use Mg2+ as an allosteric activator. Mg2+ functions allosterically by binding to an intersubunit interface that is present in the octamer but absent in the hexamer. This conformational selection allosteric mechanism is purported to be essential to avoid the untimely accumulation of phototoxic chlorophyll precursors in plants. For those PBGSs that do not use the allosteric Mg2+, there is a spatially equivalent arginine-derived guanidium group. Deprotonation of this residue promotes formation of the hexamer and accounts for the basic arm of the bell-shaped pH vs activity profile of human PBGS. A human inborn error of metabolism known as ALAD porphyria is attributed to PBGS variants that favor the hexameric assembly. The existence of one such variant, F12L, which dramatically stabilizes the human PBGS hexamer, allowed crystal structure determination for the hexamer. Without this crystal structure and octameric PBGS structures containing the allosteric Mg2+, it would have been difficult to decipher the structural basis for PBGS allostery. The requirement for multimer dissociation as an intermediate step in PBGS allostery was established by monitoring subunit disproportionation during the turnover-dependent transition of heteromeric PBGS (comprised of human wild type and F12L) from hexamer to octamer. One outcome of these studies was the definition of the dissociative morpheein model of protein allostery. The phylogenetically variable time scales for PBGS multimer interconversion result in atypical kinetic and biophysical behaviors. These behaviors can serve to identify other proteins that use the morpheein model of protein allostery.
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Affiliation(s)
- Eileen K. Jaffe
- Fox Chase Cancer Center, Temple University Health System, 333 Cottman Avenue, Philadelphia, Pennsylvania 19111, United States
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9
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Tian BX, Erdtman E, Eriksson LA. Catalytic mechanism of porphobilinogen synthase: the chemical step revisited by QM/MM calculations. J Phys Chem B 2012; 116:12105-12. [PMID: 22974111 DOI: 10.1021/jp304743c] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Porphobilinogen synthase (PBGS) catalyzes the asymmetric condensation and cyclization of two 5-aminolevulinic acid (5-ALA) substrate molecules to give porphobilinogen (PBG). The chemical step of PBGS is herein revisited using QM/MM (ONIOM) calculations. Two different protonation states and several different mechanisms are considered. Previous mechanisms based on DFT-only calculations are shown unlikely to occur. According to these new calculations, the deprotonation step rather than ring closure is rate-limiting. Both the C-C bond formation first mechanism and the C-N bond formation first mechanism are possible, depending on how the A-site ALA binds to the enzyme. We furthermore propose that future work should focus on the substrate binding step rather than the enzymatic mechanism.
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Affiliation(s)
- Bo-Xue Tian
- School of Chemistry, National University of Ireland-Galway, Galway, Ireland
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10
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Jaffe EK, Lawrence SH. Allostery and the dynamic oligomerization of porphobilinogen synthase. Arch Biochem Biophys 2011; 519:144-53. [PMID: 22037356 DOI: 10.1016/j.abb.2011.10.010] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2011] [Revised: 10/12/2011] [Accepted: 10/13/2011] [Indexed: 10/16/2022]
Abstract
The structural basis for allosteric regulation of porphobilinogen synthase (PBGS) is modulation of a quaternary structure equilibrium between octamer and hexamer (via dimers), which is represented schematically as 8mer ⇔ 2mer ⇔ 2mer∗⇔ 6mer∗. The "∗" represents a reorientation between two domains of each subunit that occurs in the dissociated state because it is sterically forbidden in the larger multimers. Allosteric effectors of PBGS are both intrinsic and extrinsic and are phylogenetically variable. In some species this equilibrium is modulated intrinsically by magnesium which binds at a site specific to the 8mer. In other species this equilibrium is modulated intrinsically by pH with the guanidinium group of an arginine being spatially equivalent to the allosteric magnesium ion. In humans, disease associated variants all shift the equilibrium toward the 6mer∗ relative to wild type. The 6mer∗ has a surface cavity that is not present in the 8mer and is proposed as a small molecule allosteric binding site. In silico and in vitro approaches have revealed species-specific allosteric PBGS inhibitors that stabilize the 6mer∗. Some of these inhibitors are drugs in clinical use leading to the hypothesis that extrinsic allosteric inhibition of human PBGS could be a mechanism for drug side effects.
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Affiliation(s)
- Eileen K Jaffe
- Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA.
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11
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Jaffe EK, Shanmugam D, Gardberg A, Dieterich S, Sankaran B, Stewart LJ, Myler PJ, Roos DS. Crystal structure of Toxoplasma gondii porphobilinogen synthase: insights on octameric structure and porphobilinogen formation. J Biol Chem 2011; 286:15298-307. [PMID: 21383008 PMCID: PMC3083160 DOI: 10.1074/jbc.m111.226225] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2011] [Revised: 03/03/2011] [Indexed: 11/06/2022] Open
Abstract
Porphobilinogen synthase (PBGS) is essential for heme biosynthesis, but the enzyme of the protozoan parasite Toxoplasma gondii (TgPBGS) differs from that of its human host in several important respects, including subcellular localization, metal ion dependence, and quaternary structural dynamics. We have solved the crystal structure of TgPBGS, which contains an octamer in the crystallographic asymmetric unit. Crystallized in the presence of substrate, each active site contains one molecule of the product porphobilinogen. Unlike prior structures containing a substrate-derived heterocycle directly bound to an active site zinc ion, the product-bound TgPBGS active site contains neither zinc nor magnesium, placing in question the common notion that all PBGS enzymes require an active site metal ion. Unlike human PBGS, the TgPBGS octamer contains magnesium ions at the intersections between pro-octamer dimers, which are presumed to function in allosteric regulation. TgPBGS includes N- and C-terminal regions that differ considerably from previously solved crystal structures. In particular, the C-terminal extension found in all apicomplexan PBGS enzymes forms an intersubunit β-sheet, stabilizing a pro-octamer dimer and preventing formation of hexamers that can form in human PBGS. The TgPBGS structure suggests strategies for the development of parasite-selective PBGS inhibitors.
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Affiliation(s)
- Eileen K. Jaffe
- From the Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111
| | | | - Anna Gardberg
- Emerald BioStructures, Inc., Bainbridge Island, Washington 98110
- the Seattle Structural Genomics Center for Infectious Disease, Seattle, Washington 98109
| | - Shellie Dieterich
- Emerald BioStructures, Inc., Bainbridge Island, Washington 98110
- the Seattle Structural Genomics Center for Infectious Disease, Seattle, Washington 98109
| | | | - Lance J. Stewart
- Emerald BioStructures, Inc., Bainbridge Island, Washington 98110
- the Seattle Structural Genomics Center for Infectious Disease, Seattle, Washington 98109
| | - Peter J. Myler
- the Seattle Biomedical Research Institute, Seattle, Washington 98109 and the Departments of Global Health and Medical Education & Biomedical Informatics, University of Washington, Seattle, Washington 98195, and
- the Seattle Structural Genomics Center for Infectious Disease, Seattle, Washington 98109
| | - David S. Roos
- the Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104
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12
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Erdtman E, Bushnell EAC, Gauld JW, Eriksson LA. Computational Insights into the Mechanism of Porphobilinogen Synthase. J Phys Chem B 2010; 114:16860-70. [DOI: 10.1021/jp103590d] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Edvin Erdtman
- School of Science and Technology, Örebro Life Science Center and Modeling and Simulation Research Center, Örebro University, Örebro, Sweden; Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada; and School of Chemistry, NUI Galway, Galway, Ireland
| | - Eric A. C. Bushnell
- School of Science and Technology, Örebro Life Science Center and Modeling and Simulation Research Center, Örebro University, Örebro, Sweden; Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada; and School of Chemistry, NUI Galway, Galway, Ireland
| | - James W. Gauld
- School of Science and Technology, Örebro Life Science Center and Modeling and Simulation Research Center, Örebro University, Örebro, Sweden; Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada; and School of Chemistry, NUI Galway, Galway, Ireland
| | - Leif A. Eriksson
- School of Science and Technology, Örebro Life Science Center and Modeling and Simulation Research Center, Örebro University, Örebro, Sweden; Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada; and School of Chemistry, NUI Galway, Galway, Ireland
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13
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Frère F, Nentwich M, Gacond S, Heinz DW, Neier R, Frankenberg-Dinkel N. Probing the active site of Pseudomonas aeruginosa porphobilinogen synthase using newly developed inhibitors. Biochemistry 2006; 45:8243-53. [PMID: 16819823 DOI: 10.1021/bi052611f] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Porphobilinogen synthase catalyzes the first committed step of the tetrapyrrole biosynthesis pathway. In an aldol-like condensation, two molecules of 5-aminolevulinic acid (ALA) form the first pyrrole, porphobilinogen. Newly synthesized analogues of a reaction intermediate of porphobilinogen synthase have been employed in studying the active site and the catalytic mechanism of this early enzyme of tetrapyrrole biosynthesis. This study combines structural and kinetic evaluation of the inhibition potency of these inhibitors. In addition, one of the determined protein structures provides for the first time structural evidence of a magnesium ion in the active site. From these results, we can corroborate an earlier postulated enzymatic mechanism that starts with formation of a C-C bond, linking C3 of the A-side ALA to C4 of the P-side ALA through an aldole addition. The obtained data are discussed with respect to the current literature.
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Affiliation(s)
- Frederic Frère
- Institute for Microbiology, Technical University Braunschweig, Spielmannstrasse 7, D-38106 Braunschweig, Germany
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14
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Tang L, Stith L, Jaffe EK. Substrate-induced interconversion of protein quaternary structure isoforms. J Biol Chem 2005; 280:15786-93. [PMID: 15710608 DOI: 10.1074/jbc.m500218200] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Human porphobilinogen synthase (PBGS) can exist in two dramatically different quaternary structure isoforms, which have been proposed to be in dynamic equilibrium. The quaternary structure isoforms of PBGS result from two alternative conformations of the monomer; one monomer structure assembles into a high activity octamer, whereas the other monomer structure assembles into a low activity hexamer. The kinetic behavior of these oligomers led to the hypothesis that turnover facilitates the interconversion of the oligomeric structures. The current work demonstrates that the interactions of ligands at the enzyme active site promote the structural interconversion between human PBGS quaternary structure isoforms, favoring formation of the octamer. This observation illustrates that the assembly and disassembly of oligomeric proteins can be facilitated by the protein motions that accompany enzymatic catalysis.
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Affiliation(s)
- Lei Tang
- Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA
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15
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Coates L, Beaven G, Erskine PT, Beale SI, Avissar YJ, Gill R, Mohammed F, Wood SP, Shoolingin-Jordan P, Cooper JB. The X-ray structure of the plant like 5-aminolaevulinic acid dehydratase from Chlorobium vibrioforme complexed with the inhibitor laevulinic acid at 2.6 A resolution. J Mol Biol 2004; 342:563-70. [PMID: 15327955 DOI: 10.1016/j.jmb.2004.07.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2004] [Revised: 06/28/2004] [Accepted: 07/09/2004] [Indexed: 11/29/2022]
Abstract
5-Aminolaevulinic acid dehydratase (ALAD), an early enzyme of the tetrapyrrole biosynthesis pathway, catalyses the dimerisation of 5-aminolaevulinic acid to form the pyrrole, porphobilinogen. ALAD from Chlorobium vibrioforme is shown to form a homo-octameric structure with 422 symmetry in which each subunit adopts a TIM-barrel fold with a 30 residue N-terminal arm extension. Pairs of monomers associate with their arms wrapped around each other. Four of these dimers interact principally via their arm regions to form octamers in which each active site is located on the surface. The active site contains two invariant lysine residues (200 and 253), one of which (Lys253) forms a Schiff base link with the bound substrate analogue, laevulinic acid. The carboxyl group of the laevulinic acid forms hydrogen bonds with the side-chains of Ser279 and Tyr318. The structure was examined to determine the location of the putative active-site magnesium ion, however, no evidence for the metal ion was found in the electron density map. This is in agreement with previous kinetic studies that have shown that magnesium stimulates but is not required for activity. A different site close to the active site flap, in which a putative magnesium ion is coordinated by a glutamate carboxyl and five solvent molecules may account for the stimulatory properties of magnesium ions on the enzyme.
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Affiliation(s)
- Leighton Coates
- School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton SO16 7PX, UK.
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16
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Abstract
Porphobilinogen synthase (PBGS) catalyzes the first common reaction in the biosynthesis of the tetrapyrroles, the asymmetric condensation of two molecules of delta-aminolevulinic acid to form porphobilinogen. There is a variable requirement for an essential active site zinc that necessitates consideration of PBGS as an enzyme that may exhibit phylogenetic diversity in its chemical reaction mechanism. Recent crystal structures suggest reaction mechanisms that involve two covalent Schiff base linkages between adjacent active site lysine residues and each of the two substrate molecules. The reaction appears to stall at a covalently bound almost-product intermediate that is poised for breakdown to product upon binding of a substrate molecule to an adjacent active site and a subsequent conformational change.
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Affiliation(s)
- Eileen K Jaffe
- Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA.
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17
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Jaffe EK. An unusual phylogenetic variation in the metal ion binding sites of porphobilinogen synthase. CHEMISTRY & BIOLOGY 2003; 10:25-34. [PMID: 12573695 DOI: 10.1016/s1074-5521(02)00296-x] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Porphobilinogen synthase (PBGS), which catalyzes the first common step in tetrapyrrole biosynthesis, contains a unique phylogenetic variation in the use of metal ions. Using sequence, structure, and enzymological information, this work codifies the phylogenetic segregation of metal utilization in PBGS from archaea, bacteria, and eucarya. All PBGS contain an active site metal binding sequence, determined herein to be either DXCXCX(Y/F)X(3)G(H/Q)CG or DXALDX(Y/F)X(3)G(H/Q)DG. The former dictates a requirement for zinc. Most PBGS that do not require zinc require magnesium and/or potassium instead. Most PBGS are also found to contain the binding determinants for an allosteric magnesium that resides outside the active site. The phylogenetic distribution of PBGS metal ion utilization suggests that the primordial PBGS required zinc and supports a hypothesis that the loss of the zinc site was concurrent with the advent of oxygenic photosynthesis.
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Affiliation(s)
- Eileen K Jaffe
- Institute for Cancer Research, Fox Chase Cancer Center, 7701 Burholme Avenue, Philadelphia, PA 19111, USA.
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18
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Frère F, Schubert WD, Stauffer F, Frankenberg N, Neier R, Jahn D, Heinz DW. Structure of porphobilinogen synthase from Pseudomonas aeruginosa in complex with 5-fluorolevulinic acid suggests a double Schiff base mechanism. J Mol Biol 2002; 320:237-47. [PMID: 12079382 DOI: 10.1016/s0022-2836(02)00472-2] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
All natural tetrapyrroles, including hemes, chlorophylls and vitamin B12, share porphobilinogen (PBG) as a common precursor. Porphobilinogen synthase (PBGS) synthesizes PBG through the asymmetric condensation of two molecules of aminolevulinic acid (ALA). Crystal structures of PBGS from various sources confirm the presence of two distinct binding sites for each ALA molecule, termed A and P. We have solved the structure of the active-site variant D139N of the Mg2+-dependent PBGS from Pseudomonas aeruginosa in complex with the inhibitor 5-fluorolevulinic acid at high resolution. Uniquely, full occupancy of both substrate binding sites each by a single substrate-like molecule was observed. Both inhibitor molecules are covalently bound to two conserved, active-site lysine residues, Lys205 and Lys260, through Schiff bases. The active site now also contains a monovalent cation that may critically enhance enzymatic activity. Based on these structural data, we postulate a catalytic mechanism for P. aeruginosa PBGS initiated by a C-C bond formation between A and P-side ALA, followed by the formation of the intersubstrate Schiff base yielding the product PBG.
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Affiliation(s)
- Frederic Frère
- Institute of Microbiology, Technical University Braunschweig, Spielmannstrasse 7, D-38106 Braunschweig, Germany
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19
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Jaffe EK, Kervinen J, Martins J, Stauffer F, Neier R, Wlodawer A, Zdanov A. Species-specific inhibition of porphobilinogen synthase by 4-oxosebacic acid. J Biol Chem 2002; 277:19792-9. [PMID: 11909869 DOI: 10.1074/jbc.m201486200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Porphobilinogen synthase (PBGS) catalyzes the condensation of two molecules of 5-aminolevulinic acid (ALA), an essential step in tetrapyrrole biosynthesis. 4-Oxosebacic acid (4-OSA) and 4,7-dioxosebacic acid (4,7-DOSA) are bisubstrate reaction intermediate analogs for PBGS. We show that 4-OSA is an active site-directed irreversible inhibitor for Escherichia coli PBGS, whereas human, pea, Pseudomonas aeruginosa, and Bradyrhizobium japonicum PBGS are insensitive to inhibition by 4-OSA. Some variants of human PBGS (engineered to resemble E. coli PBGS) have increased sensitivity to inactivation by 4-OSA, suggesting a structural basis for the specificity. The specificity of 4-OSA as a PBGS inhibitor is significantly narrower than that of 4,7-DOSA. Comparison of the crystal structures for E. coli PBGS inactivated by 4-OSA versus 4,7-DOSA shows significant variation in the half of the inhibitor that mimics the second substrate molecule (A-side ALA). Compensatory changes occur in the structure of the active site lid, which suggests that similar changes normally occur to accommodate numerous hybridization changes that must occur at C3 of A-side ALA during the PBGS-catalyzed reaction. A comparison of these with other PBGS structures identifies highly conserved active site water molecules, which are isolated from bulk solvent and implicated as proton acceptors in the PBGS-catalyzed reaction.
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Affiliation(s)
- Eileen K Jaffe
- Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
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20
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Jaffe EK, Abrams WR, Kaempfen HX, Harris KA. 5-Chlorolevulinate modification of porphobilinogen synthase identifies a potential role for the catalytic zinc. Biochemistry 2002; 31:2113-23. [PMID: 1346974 DOI: 10.1021/bi00122a032] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Porphobilinogen synthase (PBGS) is a Zn(II) metalloenzyme which catalyzes the asymmetric condensation of two molecules of 5-aminolevulinate (ALA). The nitrogen of the first substrate ends up in the pyrrole ring of product (P-side ALA); by contrast, the nitrogen of the second substrate molecule remains an amino group (A-side ALA). A reactive mimic of the substrate molecules, 5-chlorolevulinate (5-CLA), has been prepared and used as an active site directed irreversible inhibitor of PBGS. Native octameric PBGS binds eight substrate molecules and eight Zn(II) ions, with two types of sites for each ligand. As originally demonstrated by Seehra and Jordan [(1981) Eur. J. Biochem. 113, 435-446], 5-CLA inactivates the enzyme at the site where one of the two substrate molecules binds, and modification at four sites per octamer (one per active site) affords near-total inactivation. Here we report that 5-CLA-modified PBGS (5-CLA-PBGS) can bind up to four substrate molecules and four Zn(II) ions. Contrary to the conclusion of Seehra and Jordan, we find that the preferential site of 5-CLA inactivation is the A-side ALA binding site. On the basis of the dissociation constants, the metal ion binding sites lost upon 5-CLA modification are assigned to the four catalytic Zn(II) sites. 5-CLA-PBGS is shown to be modified at cysteine-223 on half of the subunits. We conclude that cysteine-223 is near the amino group of A-side ALA and propose that this cysteine is a ligand to the catalytic Zn(II). The vacant substrate binding site on 5-CLA-PBGS is that of P-side ALA. We have used 13C and 15N NMR to view [4-13C]ALA and [15N]ALA bound to 5-CLA-PBGS. The NMR results are nearly identical to those obtained previously for the enzyme-bound P-side Schiff base intermediate [Jaffe et al. (1990) Biochemistry 29, 8345-8350]. It appears that, in the absence of the catalytic Zn(II), 5-CLA-PBGS does not catalyze the condensation of the amino group of the P-side Schiff base intermediate with the C4 carbonyl derived from 5-CLA. On this basis we propose that Zn(II) plays an essential role in formation of the first bond between the two substrate molecules.
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Affiliation(s)
- E K Jaffe
- Biochemistry Department, University of Pennsylvania School of Dental Medicine, Philadelphia 19104-6002
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21
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Kervinen J, Jaffe EK, Stauffer F, Neier R, Wlodawer A, Zdanov A. Mechanistic basis for suicide inactivation of porphobilinogen synthase by 4,7-dioxosebacic acid, an inhibitor that shows dramatic species selectivity. Biochemistry 2001; 40:8227-36. [PMID: 11444968 DOI: 10.1021/bi010656k] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
4,7-Dioxosebacic acid (4,7-DOSA) is an active site-directed irreversible inhibitor of porphobilinogen synthase (PBGS). PBGS catalyzes the first common step in the biosynthesis of the tetrapyrrole cofactors such as heme, vitamin B(12), and chlorophyll. 4,7-DOSA was designed as an analogue of a proposed reaction intermediate in the physiological PBGS-catalyzed condensation of two molecules of 5-aminolevulinic acid. As shown here, 4,7-DOSA exhibits time-dependent and dramatic species-specific inhibition of PBGS enzymes. IC(50) values vary from 1 microM to 2.4 mM for human, Escherichia coli, Bradyrhizobium japonicum, Pseudomonas aeruginosa, and pea enzymes. Those PBGS utilizing a catalytic Zn(2+) are more sensitive to 4,7-DOSA than those that do not. Weak inhibition of a human mutant PBGS establishes that the inactivation by 4,7-DOSA requires formation of a Schiff base to a lysine that normally forms a Schiff base intermediate to one substrate molecule. A 1.9 A resolution crystal structure of E. coli PBGS complexed with 4,7-DOSA (PDB code ) shows one dimer per asymmetric unit and reveals that the inhibitor forms two Schiff base linkages with each monomer, one to the normal Schiff base-forming Lys-246 and the other to a universally conserved "perturbing" Lys-194 (E. coli numbering). This is the first structure to show inhibitor binding at the second of two substrate-binding sites.
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Affiliation(s)
- J Kervinen
- Institute for Cancer Research, Fox Chase Cancer Center, 7701 Burholme Avenue, Philadelphia, Pennsylvania 19111, USA
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22
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Jaffe EK, Martins J, Li J, Kervinen J, Dunbrack RL. The molecular mechanism of lead inhibition of human porphobilinogen synthase. J Biol Chem 2001; 276:1531-7. [PMID: 11032836 DOI: 10.1074/jbc.m007663200] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Human porphobilinogen synthase (PBGS) is a main target in lead poisoning. Human PBGS purifies with eight Zn(II) per homo-octamer; four ZnA have predominantly nonsulfur ligands, and four ZnB have predominantly sulfur ligands. Only four Zn(II) are required for activity. To better elucidate the roles of Zn(II) and Pb(II), we produced human PBGS mutants that are designed to lack either the ZnA or ZnB sites. These proteins, MinusZnA (H131A, C223A) and MinusZnB (C122A, C124A, C132A), each become purified with four Zn(II) per octamer, thus confirming an asymmetry in the human PBGS structure. MinusZnA is fully active, whereas MinusZnB is far less active, verifying an important catalytic role for ZnB and the removed cysteine residues. Kinetic properties of the mutants and wild type proteins are described. Comparison of Pb(II) inhibition of the mutants shows that ligands to both ZnA and ZnB interact with Pb(II). The ZnB ligands preferentially interact with Pb(II). At least one ZnA ligand is responsible for the slow tight binding behavior of Pb(II). The data support a novel model where a high affinity lead site is a hybrid of the ZnA and ZnB sites. We propose that the lone electron pair of Pb(II) precludes Pb(II) to function in PBGS catalysis.
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Affiliation(s)
- E K Jaffe
- Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
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23
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Mitchell LW, Volin M, Martins J, Jaffe EK. Mechanistic implications of mutations to the active site lysine of porphobilinogen synthase. J Biol Chem 2001; 276:1538-44. [PMID: 11032841 DOI: 10.1074/jbc.m008505200] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Porphobilinogen synthase (PBGS) is a homo-octameric protein that catalyzes the complex asymmetric condensation of two molecules of 5-aminolevulinic acid (ALA). The only characterized intermediate in the PBGS-catalyzed reaction is a Schiff base that forms between the first ALA that binds and a conserved lysine, which in Escherichia coli PBGS is Lys-246 and in human PBGS is Lys-252. In this study, E. coli PBGS mutants K246H, K246M, K246W, K246N, and K246G and human PBGS mutant K252G were characterized. Alterations to this lysine result in a disabled but not totally inactive protein suggesting an alternate mechanism in which proximity and orientation are major catalytic devices. (13)C NMR studies of [3,5-(13)C]porphobilinogen bound at the active sites of the E. coli PBGS and the mutants show only minor chemical shift differences, i.e. environmental alterations. Mammalian PBGS is established to have four functional active sites, whereas the crystal structure of E. coli PBGS shows eight spatially distinct and structurally equivalent subunits. Biochemical data for E. coli PBGS have been interpreted to support both four and eight active sites. A unifying hypothesis is that formation of the Schiff base between this lysine and ALA triggers a conformational change that results in asymmetry. Product binding studies with wild-type E. coli PBGS and K246G demonstrate that both bind porphobilinogen at four per octamer although the latter cannot form the Schiff base from substrate. Thus, formation of the lysine to ALA Schiff base is not required to initiate the asymmetry that results in half-site reactivity.
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Affiliation(s)
- L W Mitchell
- Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA
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24
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Frankenberg N, Jahn D, Jaffe EK. Pseudomonas aeruginosa contains a novel type V porphobilinogen synthase with no required catalytic metal ions. Biochemistry 1999; 38:13976-82. [PMID: 10529244 DOI: 10.1021/bi9906470] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Porphobilinogen synthases (PBGS) are metalloenzymes that catalyze the first common step in tetrapyrrole biosynthesis. The PBGS enzymes have previously been categorized into four types (I-IV) by the number of Zn(2+) and/or Mg(2+) utilized at three different metal binding sites termed A, B, and C. In this study Pseudomonas aeruginosa PBGS is found to bind only four Mg(2+) per octamer as determined by atomic absorption spectroscopy, in the presence or absence of substrate/product. This is the lowest number of bound metal ions yet found for PBGS where other enzymes bind 8-16 divalent ions. These four Mg(2+) allosterically stimulate a metal ion independent catalytic activity, in a fashion dependent upon both pH and K(+). The allosteric Mg(2+) of PBGS is located in metal binding site C, which is outside the active site. No evidence is found for metal binding to the potential high-affinity active site metal binding sites A and/or B. P. aeruginosa PBGS was investigated using Mn(2+) as an EPR probe for Mg(2+), and the active site was investigated using [3,5-(13)C]porphobilinogen as an NMR probe. The magnetic resonance data exclude the direct involvement of Mg(2+) in substrate binding and product formation. The combined data suggest that P. aeruginosa PBGS represents a new type V enzyme. Type V PBGS has the remarkable ability to synthesize porphobilinogen in a metal ion independent fashion. The total metal ion stoichiometry of only 4 per octamer suggests half-sites reactivity.
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Affiliation(s)
- N Frankenberg
- Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, Albertstrasse 21, 79104 Freiburg im Breisgau, Germany
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25
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Erskine PT, Norton E, Cooper JB, Lambert R, Coker A, Lewis G, Spencer P, Sarwar M, Wood SP, Warren MJ, Shoolingin-Jordan PM. X-ray structure of 5-aminolevulinic acid dehydratase from Escherichia coli complexed with the inhibitor levulinic acid at 2.0 A resolution. Biochemistry 1999; 38:4266-76. [PMID: 10194344 DOI: 10.1021/bi982137w] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
5-Aminolevulinic acid dehydratase (ALAD), an early enzyme of the tetrapyrrole biosynthesis pathway, catalyzes the dimerization of 5-aminolevulinic acid to form the pyrrole, porphobilinogen. ALAD from Escherichia coli is shown to form a homo-octameric structure with 422 symmetry in which each subunit adopts the TIM barrel fold with a 30-residue N-terminal arm. Pairs of monomers associate with their arms wrapped around each other. Four of these dimers interact, principally via their arm regions, to form octamers in which each active site is located on the surface. The active site contains two lysine residues (195 and 247), one of which (Lys 247) forms a Schiff base link with the bound substrate analogue, levulinic acid. Of the two substrate binding sites (referred to as A and P), our analysis defines the residues forming the P-site, which is where the first ALA molecule to associate with the enzyme binds. The carboxyl group of the levulinic acid moiety forms hydrogen bonds with the side chains of Ser 273 and Tyr 312. In proximity to the levulinic acid is a zinc binding site formed by three cysteines (Cys 120, 122, and 130) and a solvent molecule. We infer that the second substrate binding site (or A-site) is located between the triple-cysteine zinc site and the bound levulinic acid moiety. Two invariant arginine residues in a loop covering the active site (Arg 205 and Arg 216) appear to be appropriately placed to bind the carboxylate of the A-site substrate. Another metal binding site, close to the active site flap, in which a putative zinc ion is coordinated by a carboxyl and five solvent molecules may account for the activating properties of magnesium ions.
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Affiliation(s)
- P T Erskine
- Division of Biochemistry and Molecular Biology, School of Biological Sciences, University of Southampton, U.K
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26
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Shimoni-Livny L, Glusker JP, Bock CW. Lone Pair Functionality in Divalent Lead Compounds. Inorg Chem 1998. [DOI: 10.1021/ic970909r] [Citation(s) in RCA: 773] [Impact Index Per Article: 29.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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27
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Cheung KM, Spencer P, Timko MP, Shoolingin-Jordan PM. Characterization of a recombinant pea 5-aminolevulinic acid dehydratase and comparative inhibition studies with the Escherichia coli dehydratase. Biochemistry 1997; 36:1148-56. [PMID: 9033406 DOI: 10.1021/bi961215h] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Pea 5-aminolevulinic acid dehydratase (ALAD) was purified 200-fold from a recombinant overproducing strain of Escherichia coli, yielding an octameric enzyme with a specific activity of 280 units mg-1. Divalent metal ions were essential, Mg2+, Mn2+, and Co2+ ions all supporting activity, whereas Zn2+ ions could not. Equilibrium dialysis and atomic absorption studies revealed two Mg2+ ion binding sites per subunit. Pea ALAD bound the substrate 5-aminolevulinic acid covalently through a Schiff base at the P-site, electrospray mass spectrometry of the reduced enzyme-ALA Schiff base complex showing the presence of one P-site per subunit. The amino acid residue modified by ALA was identified by MALDI-MS and Edman sequencing as Lys-293, analogous to the active site Lys-247 of E. coli ALAD and Lys-252 of mammalian ALAD. Comparative studies of pea ALAD with E. coli ALAD using the inhibitors 3-acetyl-4-oxoheptane-1,7-dioic acid (AOHD) and succinylacetone (SA) indicated similar modes of inhibition, with the formation of a Schiff base complex between the inhibitors and the active site lysine. Studies with the ALA homolog, 4-amino-3-oxobutanoic acid (AOB), revealed that it is specific for the A-site of both the pea and E. coli ALADs. An interesting difference exists between the enzymes, however, pea ALAD being far more susceptible to inhibition with AOB than the E. coli enzyme. AOB bound 10 times better to the A-site of pea ALAD compared to the substrate, ALA. Despite the 2000 times lower Ki of AOB for pea ALAD, no abortive Schiff base intermediate, between enzyme-bound ALA at the P-site and AOB bound at the A-site, could be demonstrated.
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Affiliation(s)
- K M Cheung
- School of Biological Sciences, Southampton University, U.K
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28
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Schroeder TM, Caspers ML. Kinetics of aluminum-induced inhibition of delta-aminolevulinic acid dehydratase in vitro. Biochem Pharmacol 1996; 52:927-31. [PMID: 8781512 DOI: 10.1016/0006-2952(96)00449-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Anemia, one consequence of aluminum toxicity, may be due to inhibition of enzymes in the heme biosynthetic pathway. In this study, the in vitro effect of aluminum on rat liver and erythrocyte delta-aminolevulinic acid dehydratase (delta-ALA dehydratase), an enzyme that is sensitive to a number of metal ions, was investigated. The presence of 1-10 microM AlCl3 caused a concentration-dependent inhibition of liver delta-ALA dehydratase activity. The Ki for AlCl3-induced inhibition of delta-ALA dehydratase was 4.1 microM, and 10 microM AlCl3 virtually abolished delta-ALA dehydratase activity (99% inhibition). Erythrocyte delta-ALA dehydratase was also inhibited by similar concentrations of AlCl3 and displayed a Ki of 1.1 microM. AlCl3 (5 microM) decreased the Vmax by 50% but did not change the Km, suggestive of reversible, noncompetitive inhibition. Sodium citrate (50 microM) when added with AlCl3 completely restored delta-ALA dehydratase activity to basal levels. Thus, disruption of delta-ALA dehydratase occurred at low micromolar levels of AlCl3 in vitro, which may help to explain abnormalities in the heme pathway in cases of aluminum poisoning.
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Affiliation(s)
- T M Schroeder
- Department of Chemistry, University of Detroit Mercy, MI 48219, USA
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29
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Appleton D, Leeper FJ. Deuterium isotope effects on porphobilinogen synthesis catalysed by 5-aminolaevulinic acid dehydratase. Bioorg Med Chem Lett 1996. [DOI: 10.1016/0960-894x(96)00199-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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30
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Petrovich RM, Litwin S, Jaffe EK. Bradyrhizobium japonicum porphobilinogen synthase uses two Mg(II) and monovalent cations. J Biol Chem 1996; 271:8692-9. [PMID: 8621501 DOI: 10.1074/jbc.271.15.8692] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Bradyrhizobium japonicum porphobilinogen synthase (B. japonicum PBGS) has been purified and characterized from an overexpression system in an Escherichia coli host (Chauhan, S., and O'Brian, M. R. (1995) J. Biol. Chem. 270, 19823-19827). B. japonicum PBGS defines a new class of PBGS protein, type IV (classified by metal ion content), which utilizes a catalytic MgA present at a stoichiometry of 4/octamer, an allosteric MgC present at a stoichiometry of 8/octamer, and a monovalent metal ion, K+. However, the divalent MgB or ZnB present in some other PBGS is not present in B. japonicum PBGS. Under optimal conditions, the Kd for MgA is <0.2 microM, and the Kd for MgC is about 40 microM. The response of B. japonicum PBGS activity to monovalent and divalent cations is mutually dependent and varies dramatically with pH. B. japonicum PBGS is also found to undergo a dynamic equilibrium between active multimeric species and inactive monomers under assay conditions, a kinetic characteristic not reported for other PBGSs. B. japonicum PBGS is the first PBGS that has been rigorously demonstrated to lack a catalytic ZnA. However, consistent with prior predictions, B. japonicum PBGS can bind Zn(II) (presumably as ZnA) at a stoichiometry of 4/octamer with a Kd of 200 microM; but this high concentration is outside a physiologically significant range.
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Affiliation(s)
- R M Petrovich
- Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA
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31
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Chemical synthesis of porphobilinogen and studies of its biosynthesis. ACTA ACUST UNITED AC 1996. [DOI: 10.1016/s1521-4478(06)80004-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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32
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Mitchell LW, Volin M, Jaffe EK. The phylogenetically conserved histidines of Escherichia coli porphobilinogen synthase are not required for catalysis. J Biol Chem 1995; 270:24054-9. [PMID: 7592604 DOI: 10.1074/jbc.270.41.24054] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Porphobilinogen synthase (PBGS) is a metalloenzyme that catalyzes the first common step of tetrapyrrole biosynthesis, the asymmetric condensation of two molecules of 5-aminolevulinic acid (ALA) to form porphobilinogen. Chemical modification data implicate histidine as a catalytic residue of PBGS from both plants and mammals. Histidine may participate in the abstraction of two non-ionizable protons from each substrate molecule at the active site. Only one histidine is species-invariant among 17 known sequences of PBGS which have high overall sequence similarity. In Escherichia coli PBGS, this histidine is His128. We performed site-directed mutagenesis on His128, replacing it with alanine. The mutant protein H128A is catalytically active. His128 is part of a histidine- and cysteine-rich region of the sequence that is implicated in metal binding. The apparent Kd for Zn(II) binding to H128A is about an order of magnitude higher than for the wild type protein. E. coli PBGS also contains His126 which is conserved through the mammalian, fungal, and some bacterial PBGS. We mutated His126 to alanine, and both His126 and His128 simultaneously to alanine. All mutant proteins are catalytically competent; the Vmax values for H128A (44 units/mg), H126A (75 units/mg), and H126/128A (61 units/mg) were similar to wild type PBGS (50 units/mg) in the presence of saturating concentrations of metal ions. The apparent Kd for Zn(II) of H126A and H126/128A is not appreciably different from wild type. The activity of wild type and mutant proteins are all stimulated by an allosteric Mg(II); the mutant proteins all have a reduced affinity for Mg(II). We observe a pKa of approximately 7.5 in the wild type PBGS kcat/Km pH profile as well as in those of H128A and H126/128A, suggesting that this pKa is not the result of protonation/deprotonation of one of these histidines. H128A and H126/128A have a significantly increased Km value for the substrate ALA. This is consistent with a role for one or both of these histidines as a ligand to the required Zn(II) of E. coli PBGS, which is known to participate in substrate binding. Past chemical modification may have inactivated the PBGS by blocking Zn(II) and ALA binding. In addition, the decreased Km for E. coli PBGS at basic pH allows for the quantitation of active sites at four per octamer.
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Affiliation(s)
- L W Mitchell
- Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA
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Abstract
Porphobilinogen is the monopyrrole precursor of all biological tetrapyrroles. The biosynthesis of porphobilinogen involves the asymmetric condensation of two molecules of 5-aminolevulinate and is carried out by the enzyme porphobilinogen synthase (PBGS), also known as 5-aminolevulinate dehydratase. This review documents what is known about the mechanism of the PBGS-catalyzed reaction. The metal ion constituents of PBGS are of particular interest because PBGS is a primary target for the environmental toxin lead. Mammalian PBGS contains two zinc ions at each active site. Bacterial and plant PBGS use a third metal ion, magnesium, as an allosteric activator. In addition, some bacterial and plant PBGS may use magnesium in place of one or both of the zinc ions of mammalian PBGS. These phylogenetic variations in metal ion usage are described along with a proposed rationale for the evolutionary divergence in metal ion usage. Finally, I describe what is known about the structure of PBGS, an enzyme which has as yet eluded crystal structure determination.
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Affiliation(s)
- E K Jaffe
- Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA
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Jaffe EK. Predicting the Zn(II) Ligands in Metalloproteins: Case Study, Porphobilinogen Synthase. COMMENT INORG CHEM 1993. [DOI: 10.1080/02603599308035837] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Markham GD, Myers CB, Harris KA, Volin M, Jaffe EK. Spatial proximity and sequence localization of the reactive sulfhydryls of porphobilinogen synthase. Protein Sci 1993; 2:71-9. [PMID: 8382991 PMCID: PMC2142303 DOI: 10.1002/pro.5560020107] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The zinc metalloenzyme porphobilinogen synthase (PBGS) contains several functionally important, but previously unidentified, reactive sulfhydryl groups. The enzyme has been modified with the reversible sulfhydryl-specific nitroxide spin label derivative of methyl methanethiosulfonate (MMTS), (1-oxyl-2,2,5,5-tetramethyl-delta 3-pyrroline-3-methyl)methanethiosulfonate (SL-MMTS) (Berliner, L. J., Grunwald, J., Hankovszky, H. O., & Hideg, K., 1982, Anal. Biochem. 119, 450-455). EPR spectra show that SL-MMTS labels three groups per PBGS subunit (24 per octamer), as does MMTS. EPR signals reflecting nitroxides of different mobilities are observed. Two of the three modified cysteines have been identified as Cys-119 and Cys-223 by sequencing peptides produced by an Asp-N protease digest of the modified protein. Because MMTS-reactive thiols have been implicated as ligands to the required Zn(II), EPR spectroscopy has been used to determine the spatial proximity of the modified cysteine residues. A forbidden (delta m = 2) EPR transition is observed indicating a through-space dipolar interaction between at least two of the nitroxides. The relative intensity of the forbidden and allowed transitions show that at least two of the unpaired electrons are within at most 7.6 A of each other. SL-MMTS-modified PBGS loses all Zn(II) and cannot catalyze product formation. The modified enzyme retains the ability to bind one of the two substrates at each active site. Binding of this substrate has no influence on the EPR spectral properties of the spin-labeled enzyme, or on the rate of release of the nitroxides when 2-mercaptoethanol is added.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- G D Markham
- Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111
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Boese Q, Spano A, Li J, Timko M. Aminolevulinic acid dehydratase in pea (Pisum sativum L.). Identification of an unusual metal-binding domain in the plant enzyme. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(19)47339-0] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Jordan PM. Chapter 1 The biosynthesis of 5-aminolaevulinic acid and its transformation into uroporphyrinogen III. BIOSYNTHESIS OF TETRAPYRROLES 1991. [DOI: 10.1016/s0167-7306(08)60108-8] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Block C, Lohmann RD, Beyersmann D. Probing of active site residues of the zinc enzyme 5-aminolevulinate dehydratase by spin and fluorescence labels. BIOLOGICAL CHEMISTRY HOPPE-SEYLER 1990; 371:1145-52. [PMID: 1965291 DOI: 10.1515/bchm3.1990.371.2.1145] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
5-Aminolevulinate dehydratase from bovine liver requires Zn(II) for its activity and is inhibited by micromolecular concentrations of Pb(II). To elucidate the structure of the active site and its interactions between the active site and the metal binding site we labeled the active site for fluorescence studies and ESR spectroscopy. o-Phthalaldehyde reacted with active site lysyl and cysteinyl residues to form a fluorescent isoindole derivative. The fluorescence energy was independent of the deprivation of Zn(II) and of its substitution by the inhibitory Pb(II). For ESR-studies five iodoacetamide and four isothiocyanate pyrrolidine-N-oxyl derivatives with various spacer lengths were used to label the active site cysteinyl and lysyl residues, respectively. The ESR spectra of the modified enzyme preparations exhibited a significant immobilization of all labels, even with the longest spacers employed. Obviously the reactive cysteine is buried more than 12 A, and the active site lysine more than 11 A in a cleft of the enzyme structure. Zn(II) deprivation from the iodoacetamide spin-labeled enzyme caused a marked reversible increase in label mobility, whereas the Pb(II) substituted enzyme exhibited a smaller mobilization of the label. These results are interpreted by a model of the active site where the reactive cysteinyl and the lysyl side groups are close enough to be crosslinked by o-phthalaldehyde within a distance of 3 A. A structural role is assigned to Zn(II) in the enzyme, since Zn(II) deprivation does not alter the fluorescence of the isoindole derivative and increases the mobility of the cysteine-bound spin labels in the active site cleft.
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Affiliation(s)
- C Block
- Institut für Zellbiologie, Biochemie und Biotechnologie, Universität Bremen
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Jaffe EK, Markham GD, Rajagopalan JS. 15N and 13C NMR studies of ligands bound to the 280,000-dalton protein porphobilinogen synthase elucidate the structures of enzyme-bound product and a Schiff base intermediate. Biochemistry 1990; 29:8345-50. [PMID: 2252894 DOI: 10.1021/bi00488a021] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Porphobilinogen synthase (PBGS) catalyzes the asymmetric condensation of two molecules of 5-aminolevulinic acid (ALA). Despite the 280,000-dalton size of PBGS, much can be learned about the reaction mechanism through 13C and 15N NMR. To our knowledge, these studies represent the largest protein complex for which individual nuclei have been characterized by 13C or 15N NMR. Here we extend our 13C NMR studies to PBGS complexes with [3,3-2H2,3-13C]ALA and report 15N NMR studies of [15N]ALA bound to PBGS. As in our previous 13C NMR studies, observation of enzyme-bound 15N-labeled species was facilitated by deuteration at nitrogens that are attached to slowly exchanging hydrogens. For holo-PBGS at neutral pH, the NMR spectra reflect the structure of the enzyme-bound product porphobilinogen (PBG), whose chemical shifts are uniformly consistent with deprotonation of the amino group whose solution pKa is 11. Despite this local environment, the protons of the amino group are in rapid exchange with solvent (kexchange greater than 10(2) s-1). For methyl methanethiosulfonate (MMTS) modified PBGS, the NMR spectra reflect the chemistry of an enzyme-bound Schiff base intermediate that is formed between C4 of ALA and an active-site lysine. The 13C chemical shift of [3,3-2H2,3-13C]ALA confirms that the Schiff base is an imine of E stereochemistry. By comparison to model imines formed between [15N]ALA and hydrazine or hydroxylamine, the 15N chemical shift of the enzyme-bound Schiff base suggests that the free amino group is an environment resembling partial deprotonation; again the protons are in rapid exchange with solvent. Deprotonation of the amino group would facilitate formation of a Schiff base between the amino group of the enzyme-bound Schiff base and C4 of the second ALA substrate. This is the first evidence supporting carbon-nitrogen bond formation as the initial site of interaction between the two substrate molecules.
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Affiliation(s)
- E K Jaffe
- Biochemistry Department, University of Pennsylvania School of Dental Medicine, Philadelphia 19104-6002
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Fukuda H, Paredes SR, Batlle AM. Active site histidine in pig liver aminolevulic acid dehydratase modified by diethylpyrocarbonate and protected by Zn2+ ions. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. B, COMPARATIVE BIOCHEMISTRY 1988; 91:285-91. [PMID: 3197399 DOI: 10.1016/0305-0491(88)90144-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
1. The effect of diethylpyrocarbonate (DEP) (0.1-0.35 mM) on the purified pig liver amino-levulic acid dehydratase (ALA-D) containing 0.3 g-atoms Zn/subunit, under different pHs (6.0-7.5), temperature (0-18 degrees C) and time (0-60 min) was studied. 2. Three histidyl residues/subunit were modified by DEP (0.2 mM, pH 6.8), but activity was completely lost after the first one had reacted, indicating the presence of one histidine residue essential for ALA-D catalysis. Reactivation by treatment with hydroxylamine (0.7 mM, pH 7.0) confirmed that only histidine and no other nucleophile amino acids were directly involved in DEP inhibition. 3. Zn ions (0.5 mM) and the substrate ALA (5-10 mM) protected against DEP inactivation, protection was dependent on pH. 4. Sn, Se, Hg, Cd, Mn, Co and Pb (0.01-0.1 mM) did not significantly protect ALA-D against inactivation. 5. It is concluded that the substrate and Zn binding sites and the essential histidyl residues are in close proximity in the active center. It is proposed that in the catalytic synthesis of porphobilinogen from ALA, histidine groups have the specific role of transporting protons from the aqueous media to a hydrophobic active site.
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Affiliation(s)
- H Fukuda
- Centro de Investigaciones sobre Porfirinas y Porfirias-CIPYP (CONICET-FCEyN, UBA), Ciudad Universitaria, Buenos Aires, Argentine
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Astrin KH, Bishop DF, Wetmur JG, Kaul B, Davidow B, Desnick RJ. delta-Aminolevulinic acid dehydratase isozymes and lead toxicity. Ann N Y Acad Sci 1987; 514:23-9. [PMID: 3442386 DOI: 10.1111/j.1749-6632.1987.tb48757.x] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
ALAD is a zinc metalloenzyme whose inhibition by lead is the first and most sensitive indicator of lead exposure and whose decreased activity has been implicated in the pathogenesis of lead poisoning. This heme biosynthetic enzyme is encoded by a gene located at chromosome 9q34, which has two codominant alleles, ALAD1 and ALAD2. The occurrence of two frequent alleles for ALAD stimulated an investigation into the possible pharmacogenetic role of the enzyme polymorphism in lead poisoning. In a New York City population at high risk for lead exposure, individuals heterozygous or homozygous for the less common allele, ALAD2, had blood lead levels greater than or equal to 30 micrograms/dl more frequently than expected. These findings suggest a potential genetic susceptibility to lead poisoning in individuals with the ALAD 1-2 and 2-2 phenotypes.
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Affiliation(s)
- K H Astrin
- Department of Pediatrics, Mount Sinai School of Medicine, New York, New York 10029
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Schlösser M, Beyersmann D. Zinc and cadmium 5-aminolevulinate dehydratase. Metal-dependent pH profiles. BIOLOGICAL CHEMISTRY HOPPE-SEYLER 1987; 368:1469-77. [PMID: 3435644 DOI: 10.1515/bchm3.1987.368.2.1469] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Native 5-aminolevulinic acid dehydratase contains zinc ions, which are essential for the enzymatic activity. Replacement of zinc by cadmium yielded an active enzyme whose kinetic parameters (kkat and Km) are similar to those of the zinc enzyme in the neutral pH range. However, the pH profiles of kcat and Km were different due to different pKa values. Two groups both with pKa values of 6.5 in the free zinc enzyme, but with pKa values of 7.0 in the cadmium enzyme were calculated from plots of log (kcat/Km) versus pH. On the other hand, the enzyme-substrate complex is controlled by one acidic group (zinc pKa = 6.0, cadmium pKa = 6.4) and one basis group (zinc pKa = 8.2, cadmium pKa = 7.7) as calculated from plots of log kcat versus pH. The Arrhenius plots for kcat of the two enzymes show no significant difference, the free energies of activation are 77.1 kJ/mol for the zinc and 76.8 kJ/mol for the cadmium enzyme. From this and from previous work it is concluded that the metal ions are located near the active site and influence the ionisations of essential amino acid residues. From the pH profiles of the modifying reaction and inhibition by diethylpyrocarbonate a histidinyl residue is inferred as one of the ionisable groups of the active site.
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Affiliation(s)
- M Schlösser
- Fachbereich Biologie/Chemie, Universität Bremen
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