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Valle-Altamirano RG, Baratto MC, Badillo-Ramírez I, Gasteazoro F, Pogni R, Saniger JM, Valderrama B. Identification of Fe( iii)–OH species as a catalytic intermediate in plant peroxidases at high H 2O 2 concentration. NEW J CHEM 2022. [DOI: 10.1039/d1nj04837f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
The structure for compound III formed after exposure of plant heme peroxidases to excess H2O2 seems to be a hydroxylated form, providing new evidence for understanding the structural basis of the substrate-induced suicidal behavior of these enzymes.
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Affiliation(s)
- Rodolfo G. Valle-Altamirano
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad, 62210 Morelos, Mexico
- Facultad de Química, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510 Ciudad de México, Mexico
| | - Maria Camilla Baratto
- Department of Biotechnology, Chemistry and Pharmacy, University of Siena, Via A. Moro, 53100 Siena, Italy
| | - Isidro Badillo-Ramírez
- Instituto de Ciencias Aplicadas y Tecnología, Universidad Nacional Autónoma de México, Circuito Exterior S/N, Ciudad Universitaria, 04510, Ciudad de México, Mexico
| | - Francisco Gasteazoro
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad, 62210 Morelos, Mexico
| | - Rebecca Pogni
- Department of Biotechnology, Chemistry and Pharmacy, University of Siena, Via A. Moro, 53100 Siena, Italy
| | - José M. Saniger
- Instituto de Ciencias Aplicadas y Tecnología, Universidad Nacional Autónoma de México, Circuito Exterior S/N, Ciudad Universitaria, 04510, Ciudad de México, Mexico
| | - Brenda Valderrama
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad, 62210 Morelos, Mexico
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Powles T, Szabados B, Castellano D, Rodriguez-Vida A, Valderrama B, Crabb S, Van Der Heijden M, Pous AF, Prendergast A, Gravis G, Herranz UA, Sharma S, Ravauld A, Sethi H, Zimmerman B, Aleshin A, Kockx M, Banchereau R, Mariathasan S, Assaf ZJ. CtDNA as a predictor of outcome in patients treated with neoadjuvant atezolizumab in muscle invasive urothelial cancer. Urol Oncol 2020. [DOI: 10.1016/j.urolonc.2020.10.069] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Valderrama B, Paredes-Valdez G, Rodríguez R, Romero-Guido C, Martínez F, Martínez-Romero J, Guerrero-Galván S, Mendoza-Herrera A, Folch-Mallol JL. Assessment of non-cultured aquatic fungal diversity from different habitats in Mexico. REV MEX BIODIVERS 2016. [DOI: 10.1016/j.rmb.2016.01.013] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Gasteazoro F, Simaan AJ, Tinoco-Valencia R, Valderrama B. Validation of a general method for activity estimation of cyanide evolving oxidoreductases. Anal Biochem 2015; 471:44-50. [PMID: 25447496 DOI: 10.1016/j.ab.2014.10.021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2014] [Revised: 09/08/2014] [Accepted: 10/13/2014] [Indexed: 10/24/2022]
Abstract
Ethylene is a key molecule in organic synthesis currently produced by steam cracking of fossil hydrocarbons. In nature, ethylene is produced in higher plants by 1-aminocyclopropane-1-carboxylic acid oxidase (ACCO). Biocatalytic alternatives for ethylene production are still far from being competitive with traditional production plants. Furthermore, data dispersion shown in the literature adds uncertainty to the introduction of ACCO as a biocatalyst, especially when larger numbers of isoforms or mutants are to be compared. Here we propose a new method for measuring ACCO activity based on cyanide detection. Data provided here indicate that cyanide detection is more precise, more responsive, and much more stable than any other method tested for ACCO activity estimation so far. Briefly, enzymatically produced cyanide can be detected by its derivatization with naphthalene-2,3-dicarboxyaldehide (NDA) to generate 1-cyanobenz[f]isoindole (CBI), which is further detected by high-performance liquid chromatography (HPLC) coupled with a fluorescence detector. Cyanide can be detected in the range between 0.99 and 60.17pmol, which is three orders of magnitude more sensitive than the currently used ethylene estimation method.
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Affiliation(s)
- Francisco Gasteazoro
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62210, Mexico
| | - Ariane Jalila Simaan
- Institut des Sciences Moléculaires de Marseille, Aix Marseille Université, Centrale Marseille, CNRS, iSm2, UMR 7313, 13397 Marseille, France
| | - Raunel Tinoco-Valencia
- Unidad de Escalamiento y Planta Piloto, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62210, Mexico
| | - Brenda Valderrama
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62210, Mexico.
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Castro-Acosta RM, Rodríguez-Limas WA, Valderrama B, Ramírez OT, Palomares LA. Effect of metal catalyzed oxidation in recombinant viral protein assemblies. Microb Cell Fact 2014; 13:25. [PMID: 24533452 PMCID: PMC3928578 DOI: 10.1186/1475-2859-13-25] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2014] [Accepted: 02/10/2014] [Indexed: 11/12/2022] Open
Abstract
Background Protein assemblies, such as virus-like particles, have increasing importance as vaccines, delivery vehicles and nanomaterials. However, their use requires stable assemblies. An important cause of loss of stability in proteins is oxidation, which can occur during their production, purification and storage. Despite its importance, very few studies have investigated the effect of oxidation in protein assemblies and their structural units. In this work, we investigated the role of in vitro oxidation in the assembly and stability of rotavirus VP6, a polymorphic protein. Results The susceptibility to oxidation of VP6 assembled into nanotubes (VP6NT) and unassembled VP6 (VP6U) was determined and compared to bovine serum albumin (BSA) as control. VP6 was more resistant to oxidation than BSA, as determined by measuring protein degradation and carbonyl content. It was found that assembly protected VP6 from in vitro metal-catalyzed oxidation. Oxidation provoked protein aggregation and VP6NT fragmentation, as evidenced by dynamic light scattering and transmission electron microscopy. Oxidative damage of VP6 correlated with a decrease of its center of fluorescence spectral mass. The in vitro assembly efficiency of VP6U into VP6NT decreased as the oxidant concentration increased. Conclusions Oxidation caused carbonylation, quenching, and destruction of aromatic amino acids and aggregation of VP6 in its assembled and unassembled forms. Such modifications affected protein functionality, including its ability to assemble. That assembly protected VP6 from oxidation shows that exposure of susceptible amino acids to the solvent increases their damage, and therefore the protein surface area that is exposed to the solvent is determinant of its susceptibility to oxidation. The inability of oxidized VP6 to assemble into nanotubes highlights the importance of avoiding this modification during the production of proteins that self-assemble. This is the first time that the role of oxidation in protein assembly is studied, evidencing that oxidation should be minimized during the production process if VP6 nanotubes are required.
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Affiliation(s)
| | | | | | | | - Laura A Palomares
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, A,P, 510-3, C,P, 62210, Cuernavaca, Morelos, Mexico.
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Hernández-Montes G, Argüello JM, Valderrama B. Evolution and diversity of periplasmic proteins involved in copper homeostasis in gamma proteobacteria. BMC Microbiol 2012; 12:249. [PMID: 23122209 PMCID: PMC3548706 DOI: 10.1186/1471-2180-12-249] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2012] [Accepted: 10/25/2012] [Indexed: 12/15/2022] Open
Abstract
Background Different systems contributing to copper homeostasis in bacteria have been described in recent years involving periplasmic and transport proteins that provide resistance via metal efflux to the extracellular media (CopA/Cue, Cus, Cut, and Pco). The participation of these proteins in the assembly of membrane, periplasmic and secreted cuproproteins has also been postulated. The integration and interrelation of these systems and their apparent redundancies are less clear since they have been studied in alternative systems. Based on the idea that cellular copper is not free but rather it is transferred via protein-protein interactions, we hypothesized that systems would coevolve and be constituted by set numbers of essential components. Results By the use of a phylogenomic approach we identified the distribution of 14 proteins previously characterized as members of homeostasis systems in the genomes of 268 gamma proteobacteria. Only 3% of the genomes presented the complete systems and 5% of them, all intracellular parasites, lacked the 14 genes. Surprisingly, copper homeostatic pathways did not behave as evolutionary units with particular species assembling different combinations of basic functions. The most frequent functions, and probably because of its distribution the most vital, were copper extrusion from the cytoplasm to the periplasm performed by CopA and copper export from the cytoplasm to the extracellular space performed by CusC, which along with the remaining 12 proteins, assemble in nine different functional repertoires. Conclusions These observations suggest complex evolutionary dynamics and still unexplored interactions to achieve copper homeostasis, challenging some of the molecular transport mechanism proposed for these systems.
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Affiliation(s)
- Georgina Hernández-Montes
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av Universidad 2001 Col, Chamilpa, Cuernavaca, Mor CP 62210, México
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Bello M, Valderrama B, Serrano-Posada H, Rudiño-Piñera E. Molecular dynamics of a thermostable multicopper oxidase from Thermus thermophilus HB27: structural differences between the apo and holo forms. PLoS One 2012; 7:e40700. [PMID: 22808237 PMCID: PMC3393687 DOI: 10.1371/journal.pone.0040700] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Accepted: 06/12/2012] [Indexed: 11/19/2022] Open
Abstract
Molecular dynamic (MD) simulations have been performed on Tth-MCO, a hyperthermophilic multicopper oxidase from thermus thermophilus HB27, in the apo as well as the holo form, with the aim of exploring the structural dynamic properties common to the two conformational states. According to structural comparison between this enzyme and other MCOs, the substrate in process to electron transfer in an outer-sphere event seems to transiently occupy a shallow and overall hydrophobic cavity near the Cu type 1 (T1Cu). The linker connecting the β-strands 21 and 24 of the second domain (loop (β21–β24)D2) has the same conformation in both states, forming a flexible lid at the entrance of the electron-transfer cavity. Loop (β21–β24)D2 has been tentatively assigned a role occluding the access to the electron-transfer site. The dynamic of the loop (β21–β24)D2 has been investigated by MD simulation, and results show that the structures of both species have the same secondary and tertiary structure during almost all the MD simulations. In the simulation, loop (β21–β24)D2 of the holo form undergoes a higher mobility than in the apo form. In fact, loop (β21–β24)D2 of the holo form experiences a conformational change which enables exposure to the electron-transfer site (open conformation), while in the apo form the opposite effect takes place (closed conformation). To confirm the hypothesis that the open conformation might facilitate the transient electron-donor molecule occupation of the site, the simulation was extended another 40 ns with the electron-donor molecule docked into the protein cavity. Upon electron-donor molecule stabilization, loops near the cavity reduce their mobility. These findings show that coordination between the copper and the protein might play an important role in the general mobility of the enzyme, and that the open conformation seems to be required for the electron transfer process to T1Cu.
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Affiliation(s)
- Martiniano Bello
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
- * E-mail: (MB); (ERP)
| | - Brenda Valderrama
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
| | - Hugo Serrano-Posada
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
| | - Enrique Rudiño-Piñera
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
- * E-mail: (MB); (ERP)
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De la Mora E, Lovett JE, Blanford CF, Garman EF, Valderrama B, Rudino-Pinera E. Structural changes caused by radiation-induced reduction and radiolysis: the effect of X-ray absorbed dose in a fungal multicopper oxidase. Acta Crystallogr D Biol Crystallogr 2012; 68:564-77. [PMID: 22525754 DOI: 10.1107/s0907444912005343] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2011] [Accepted: 02/07/2012] [Indexed: 02/20/2023]
Abstract
X-ray radiation induces two main effects at metal centres contained in protein crystals: radiation-induced reduction and radiolysis and a resulting decrease in metal occupancy. In blue multicopper oxidases (BMCOs), the geometry of the active centres and the metal-to-ligand distances change depending on the oxidation states of the Cu atoms, suggesting that these alterations are catalytically relevant to the binding, activation and reduction of O(2). In this work, the X-ray-determined three-dimensional structure of laccase from the basidiomycete Coriolopsis gallica (Cg L), a high catalytic potential BMCO, is described. By combining spectroscopic techniques (UV-Vis, EPR and XAS) and X-ray crystallography, structural changes at and around the active copper centres were related to pH and absorbed X-ray dose (energy deposited per unit mass). Depletion of two of the four active Cu atoms as well as low occupancies of the remaining Cu atoms, together with different conformations of the metal centres, were observed at both acidic pH and high absorbed dose, correlating with more reduced states of the active coppers. These observations provide additional evidence to support the role of flexibility of copper sites during O(2) reduction. This study supports previous observations indicating that interpretations regarding redox state and metal coordination need to take radiation effects explicitly into account.
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Affiliation(s)
- Eugenio De la Mora
- Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Avenida Universidad 2001, Cuernavaca, Morelos 62210, Mexico
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9
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Serrano-Posada H, Valderrama B, Stojanoff V, Rudiño-Piñera E. Thermostable multicopper oxidase from Thermus thermophilus HB27: crystallization and preliminary X-ray diffraction analysis of apo and holo forms. Acta Crystallogr Sect F Struct Biol Cryst Commun 2011; 67:1595-8. [PMID: 22139175 PMCID: PMC3232148 DOI: 10.1107/s174430911103805x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2011] [Accepted: 09/17/2011] [Indexed: 11/10/2022]
Abstract
A thermostable multicopper oxidase from Thermus thermophilus HB27 (Tth-MCO) was successfully crystallized using the sitting-drop and hanging-drop vapour-diffusion methods. Crystallization conditions and preliminary X-ray diffraction data to 1.5 Å resolution obtained using synchrotron radiation at 100 K are reported. The crystals belonged to space group C222(1), with unit-cell parameters a = 93.6, b = 110.3, c = 96.3 Å. A monomer in the asymmetric unit yielded a Matthews coefficient (V(M)) of 2.60 Å(3) Da(-1) and a solvent content of 53%. An inactive enzyme form, apo-Tth-MCO, was also crystallized and diffraction data were collected to 1.7 Å resolution. In addition, a second inactive form of the enzyme, Hg-Tth-MCO, was obtained by soaking apo-Tth-MCO crystals with mercury(II) chloride and data were collected to a resolution of 1.7 Å.
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Affiliation(s)
- Hugo Serrano-Posada
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, UNAM, Avenida Universidad 2001, Chamilpa, 62210 Cuernavaca, Morelos, Mexico
| | - Brenda Valderrama
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, UNAM, Avenida Universidad 2001, Chamilpa, 62210 Cuernavaca, Morelos, Mexico
| | - Vivian Stojanoff
- NSLS, Brookhaven National Laboratory, 75 Brookhaven Avenue, Building 725D, Upton, New York 11973-5000, USA
| | - Enrique Rudiño-Piñera
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, UNAM, Avenida Universidad 2001, Chamilpa, 62210 Cuernavaca, Morelos, Mexico
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Abstract
Redox-active enzymes perform many key biological reactions. The electron transfer process is complex, not only because of its versatility, but also because of the intricate and delicate modulation exerted by the protein scaffold on the redox properties of the catalytic sites. Nowadays, there is a wealth of information available about the catalytic mechanisms of redox-active enzymes and the time is propitious for the development of projects based on the protein engineering of redox-active enzymes. In this review, we aim to provide an updated account of the available methods used for protein engineering, including both genetic and chemical tools, which are usually reviewed separately. Specific applications to redox-active enzymes are mentioned within each technology, with emphasis on those cases where the generation of novel functionality was pursued. Finally, we focus on two emerging fields in the protein engineering of redox-active enzymes: the construction of novel nucleic acid-based catalysts and the remodeling of intra-molecular electron transfer networks. We consider that the future development of these areas will represent fine examples of the concurrence of chemical and genetic tools.
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Affiliation(s)
- Gloria Saab-Rincón
- Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
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Abstract
The pathogenic yeast C. neoformans is classified into three varieties with five serotypes; var. grubii (serotype A), var. neoformans (serotype D), var. gattii (serotypes B and C), and serotype AD. Melanin is a virulence factor in the species, and its biosynthesis is catalyzed by laccase, encoded by the LAC1 gene. In order to estimate the natural variability of the LAC1 gene among Cryptococcus serotypes, the laccase protein sequence from 55 strains was determined and the phylogenetic relationships between cryptococcal and related fungal laccases revealed. The deduced laccase proteins consisted of 624 amino acid residues in serotypes A, D and AD, and 613 to 615 residues in serotypes B and C. Intra-serotype amino acid variation was marginal within serotypes A and D, and none was found within serotypes AD and C. Maximum amino acid replacement occurred in two serotype B strains. The similarity in the deduced sequence ranged from 80 to 96% between serotypes. The sequence in the copper-binding regions was strongly conserved in the five serotypes. The laccases of the five serotypes were grouped together in the same clade of the phylogenetic tree reconstructed from different fungal laccases, suggesting a monophyletic clade.
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Affiliation(s)
- Shoko Ito-Kuwa
- Advanced Research Center, Nippon Dental University at Niigata, Niigata 951-8580, Japan.
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Gil‐Rodríguez P, Ferreira‐Batista C, Vázquez‐Duhalt R, Valderrama B. A Novel Heme Peroxidase fromRaphanus sativusIntrinsically Resistant to Hydrogen Peroxide. Eng Life Sci 2008. [DOI: 10.1002/elsc.200700073] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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Wbanet S, Cayuela A, Bernal L, Valderrama B, Valero M, Ruiz M, Iglesias M, Iglesias L, Moreno J, Casas AM. Needs satisfaction for cancer patients in an ambulatory chemotherapy service (ACS). An exploratory study. J Clin Oncol 2006. [DOI: 10.1200/jco.2006.24.18_suppl.18607] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
18607 Background: ACS are currently the main way for the delivery of Chemotherapy to cancer patients. Aproximately half of them require intravenous chemotherapy and many need two or three separate lines of treatment during their clinical career. How these treatments are delivered will affect their health and quality of life. Appraisal of needs along chemotherapy process enable to identify problems related to health satisfaction status and quality of health care provided. Methods: We have evaluated the perceived needs of patients receiving ambulatory chemotherapy through an “ad hoc” questionnaire of 49 items exploring the following areas: treatment related symptoms, information and communication/interpersonal interaction, psychological, social and spiritual support, economical needs and management of health service. Results: 141 consecutive patients attending the ACS one year after its set up were evaluated. Demographics (age, gender and income), diagnosis and types of Chemotherapy (Adjuvant vs. Palliative) were considered for interrelationships. The most frequent tumors were breast and colorectal carcinoma. More than 50% of the patients reported having controlled symptoms (pain, nausea and vomiting, mucositis etc.). Information needs related to their illness and treatment were satisfied to more than half of the sample, but reported a need for more information about diagnostic procedures and prognosis; 48% perceived shortcomings in communication with their clinicians and 50% believed they received little advice about how cancer affects their sexual behaviour. Most patients (53%) reported not to need pshycological support neither for their family (60%) nor themselves, 83% not needing spiritual support and 50% were satisfied with the economical support they received. With respect to the facilities’ structure, 50% perceived enough intimacy in doctor’s offices and Chemotherapy Room and 64% felt comfortable in the waiting room but 72% perceived waiting too long before being attended by doctor’s and nurses. Conclusions: younger patients and breast cancer diagnosis are among the people that express more unsatisfaction related to the accomplishment of their needs (p < 0.05). No significant financial relationships to disclose.
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Affiliation(s)
- S. Wbanet
- Hospitales Universitarios Virgen de Rocío, Sevilla, Spain
| | - A. Cayuela
- Hospitales Universitarios Virgen de Rocío, Sevilla, Spain
| | - L. Bernal
- Hospitales Universitarios Virgen de Rocío, Sevilla, Spain
| | - B. Valderrama
- Hospitales Universitarios Virgen de Rocío, Sevilla, Spain
| | - M. Valero
- Hospitales Universitarios Virgen de Rocío, Sevilla, Spain
| | - M. Ruiz
- Hospitales Universitarios Virgen de Rocío, Sevilla, Spain
| | - M. Iglesias
- Hospitales Universitarios Virgen de Rocío, Sevilla, Spain
| | - L. Iglesias
- Hospitales Universitarios Virgen de Rocío, Sevilla, Spain
| | - J. Moreno
- Hospitales Universitarios Virgen de Rocío, Sevilla, Spain
| | - A. M. Casas
- Hospitales Universitarios Virgen de Rocío, Sevilla, Spain
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Valderrama B, García-Arellano H, Giansanti S, Baratto MC, Pogni R, Vazquez-Duhalt R. Oxidative stabilization of iso‐1‐cytochromecby redox‐inspired protein engineering. FASEB J 2006; 20:1233-5. [PMID: 16720736 DOI: 10.1096/fj.05-4173fje] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Iso-1-cytochrome c, as any other hemeprotein, is able to react with hydrogen peroxide and to engage in the peroxidase cycle. However, peroxidases are irreversibly inactivated by their substrate, hydrogen peroxide. The oxidative inactivation of hemeproteins is mechanism based and arises as the consequence of unproductive electron abstraction reactions. Protein elements, such as the porphyrin ring or the protein backbone, act as simultaneous and competing electron sources even in the presence of exogenous reducing substrates, leading to a decline in activity. It is hypothetically possible to alter the intramolecular electron transfer pathways by direct replacement of low redox potential residues around the active site; as a consequence, the inactivation process would be delayed or even suppressed. To demonstrate this hypothesis, a redox-inspired strategy was implemented until an iso-1-cytochrome c variant fully stable at catalytic concentrations of hydrogen peroxide was obtained. This variant, harboring the N52I,W59F,Y67F,K79A,F82G substitutions, preserved the catalytic performance of the parental protein but achieved a 15-fold higher total-turnover number. The phenotype of this variant was reflected in the stability of its electronic components, allowing identification of a protein-based radical intermediate mechanistically similar to Compound I of classical peroxidases. The results presented here clearly demonstrate that redox-inspired protein engineering is a useful tool for the rational modulation of intramolecular electron transfer networks.
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Affiliation(s)
- Brenda Valderrama
- Department of Cellular Engineering and Biocatalysis, Biotechnology Institute, National University of Mexico, AP 510-3, Cuernavaca, México.
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Pogni R, Baratto MC, Giansanti S, Teutloff C, Verdin J, Valderrama B, Lendzian F, Lubitz W, Vazquez-Duhalt R, Basosi R. Tryptophan-based radical in the catalytic mechanism of versatile peroxidase from Bjerkandera adusta. Biochemistry 2005; 44:4267-74. [PMID: 15766255 DOI: 10.1021/bi047474l] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Versatile peroxidase (VP) from Bjerkandera adusta is a structural hybrid between lignin (LiP) and manganese (MnP) peroxidase. This hybrid combines the catalytic properties of the two above peroxidases, being able to oxidize typical LiP and MnP substrates. The catalytic mechanism is that of classical peroxidases, where the substrate oxidation is carried out by a two-electron multistep reaction at the expense of hydrogen peroxide. Elucidation of the structures of intermediates in this process is crucial for understanding the mechanism of substrate oxidation. In this work, the reaction of H(2)O(2) with the enzyme in the absence of substrate has been investigated with electron paramagnetic resonance (EPR) spectroscopy. The results reveal an EPR signal with partially resolved hyperfine structure typical of an organic radical. The yield of this radical is approximately 30%. Progressive microwave power saturation measurements indicate that the radical is weakly coupled to a paramagnetic metal ion, suggesting an amino acid radical in moderate distance from the ferryl heme. A tryptophan radical was identified as a protein-based radical formed during the catalytic mechanism of VP from Bjerkandera adusta through X-band and high-field EPR measurements at 94 GHz, aided by computer simulations for both frequency bands. A close analysis of the theoretical model of the VP from Bjerkandera sp. shows the presence of a tryptophan residue near to the heme prosthetic group, which is solvent-exposed as in the case of LiP and other VPs. The catalytic role of this residue in a long-range electron-transfer pathway is discussed.
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Affiliation(s)
- Rebecca Pogni
- Department of Chemistry, University of Siena, via Aldo Moro, 53100 Siena, Italy.
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Jimenez-Juarez N, Roman-Miranda R, Baeza A, Sánchez-Amat A, Vazquez-Duhalt R, Valderrama B. Alkali and halide-resistant catalysis by the multipotent oxidase from Marinomonas mediterranea. J Biotechnol 2005; 117:73-82. [PMID: 15831249 DOI: 10.1016/j.jbiotec.2005.01.002] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2004] [Revised: 12/28/2004] [Accepted: 01/07/2005] [Indexed: 11/24/2022]
Abstract
The incorporation of fungal laccases into novel applications has been delayed mainly due to their intrinsic sensitivity towards halides and alkaline conditions. In order to explore new sources of enzymes we evaluated the multipotent polyphenol oxidase PPO1 from the marine bacterium Marinomonas mediterranea. Here we report that, in contrast to its fungal counterparts, PPO1 remained functional above neutral pH presenting high specificity for phenolic compounds, in particular for methoxyl-substituted mono-phenols and catechols. These properties, in addition to its tolerance towards chloride (up to 1 M) and its elevated redox potential at neutral pH (0.9 V), suggest this enzyme may be an interesting candidate for specific applications such as the Amperometric determination of phenolic compounds and bio-fuel cells.
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Affiliation(s)
- Nuria Jimenez-Juarez
- Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México, AP 510-3, Cuernavaca, Morelos CP 62250, Mexico
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17
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Necochea R, Valderrama B, Díaz-Sandoval S, Folch-Mallol JL, Vázquez-Duhalt R, Iturriaga G. Phylogenetic and biochemical characterisation of a recombinant laccase fromTrametes versicolor. FEMS Microbiol Lett 2005; 244:235-41. [PMID: 15766774 DOI: 10.1016/j.femsle.2005.01.054] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2004] [Revised: 12/08/2004] [Accepted: 01/26/2005] [Indexed: 11/30/2022] Open
Abstract
Laccases are important enzymes for bioremediation and the best-characterised are from the fungus Trametes versicolor. Here, we describe the cloning and characterisation of a new variant of laccase from T. versicolor and its expression in Saccharomyces cerevisiae. We have performed a sequence-based analysis of Trametes laccases that leads to a proposal for a new nomenclature of this fungus laccases according to their phylogenetic relationships since their nomenclature based on IPs is ambiguous. We also describe the kinetic properties of the recombinant enzyme.
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Affiliation(s)
- Rosalía Necochea
- Departamento de Biotecnología Ambiental, Centro de Investigación en Biotecnología, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, Cuernavaca, Mor. 62210, México
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18
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Abstract
The enzymatic mechanism for the transformation of organophosphorus pesticides (OPPs) by different white-rot fungi strains was studied. With the exception of Ganoderma applanatum 8168, all strains from a collection of 17 different fungi cultures were able to deplete parathion. Three strains showing the highest activities were selected for further studies: Bjerkandera adusta 8258, Pleurotus ostreatus 7989 and Phanerochaete chrysosporium 3641. These strains depleted 50 to 96% of terbufos, azinphos-methyl, phosmet and tribufos after four-days exposure to the pesticides. In order to identify the cellular localization of the transformation activity, the extracellular and microsomal fractions of Pleuronts ostreatus 7989 were evaluated in vitro. While the activities of ligninolytic enzymes (lignin peroxidase, manganese peroxidase and laccase) were detected in the extracellular fraction, no enzymatic modification of any of the five pesticides tested could be found, suggesting the intracellular origin of the transformation activity. In accordance with this observation the microsomal fraction was found able to transform three OPPs with the following rates: 10 micromol mg prot(-1) h(-1) for phosmet, 5.7 micromol mg prot(-1) h(-1) for terbufos, and 2.2 micromol mg prot(-1) h(-1) for azinphos-methyl. The products from these reactions and from the transformation of trichlorfon and malathion, were identified by mass-spectrometry. These results, supported by specific inhibition experiments and the stringent requirement for NADPH during the in vitro assays suggest the involvement of a cytochrome P450.
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Affiliation(s)
- Juan Jauregui
- Instituto de Biotecnologia, UNAM Apartado Postal 510-3, Cuernavaca, Morelos, 62250 Mexico
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19
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Abstract
Fungal laccases have been extensively exploited for industrial purposes and there is a wealth of information available regarding their reaction mechanism, biological role and several molecular aspects, including cloning, heterologous expression and transcriptional analyses. Here we present the reconstruction of the fungal laccase loci evolution inferred from the comparative analysis of 48 different sequences. The topology of the phylogenetic trees indicate that a single monophyletic branch exists for fungal laccases and that laccase isozyme genes may have evolved independently, possibly through duplication-divergence events. Laccases are copper-containing enzymes generally identified by the utilization of substituted p-diphenol substrates. Interestingly, our approach permitted the assignment of two copper-containing oxidases, preliminarily catalogued as laccases, to a different evolutionary group, distantly related to the main branch of bona fide laccases.
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Affiliation(s)
- Brenda Valderrama
- Instituto de Biotecnología, Universidad Nacional Autónoma de México, AP 510-3 Cuernavaca, Morelos, Mexico.
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20
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Medina G, Juárez K, Valderrama B, Soberón-Chávez G. Mechanism of Pseudomonas aeruginosa RhlR transcriptional regulation of the rhlAB promoter. J Bacteriol 2003; 185:5976-83. [PMID: 14526008 PMCID: PMC225020 DOI: 10.1128/jb.185.20.5976-5983.2003] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2003] [Accepted: 07/25/2003] [Indexed: 11/20/2022] Open
Abstract
Pseudomonas aeruginosa contains two transcription regulators (LasR and RhlR) that, when complexed with their specific autoinducers (3-oxo-dodecanoyl-homoserine lactone and butanoyl-homoserine lactone, respectively) activate transcription of different virulence-associated traits. We studied the RhlR-dependent transcriptional regulation of the rhlAB operon encoding rhamnosyltransferase 1, an enzyme involved in the synthesis of the surfactant monorhamnolipid, and showed that RhlR binds to a specific sequence in the rhlAB regulatory region, both in the presence and in the absence of its autoinducer. Our data suggest that in the former case it activates transcription, whereas in the latter it acts as a transcriptional repressor of this promoter. RhlR seems to repress the transcription of other quorum-sensing-regulated genes; thus, RhlR repressor activity might be of importance in the finely regulated expression of P. aeruginosa virulence-associated traits.
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Affiliation(s)
- Gerardo Medina
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
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21
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Abstract
Glucosamine-6-phosphate deaminase (EC 3.5.99.6) is an allosteric enzyme that catalyzes the reversible conversion of D-glucosamine-6-phosphate into D-fructose-6-phosphate and ammonium. Here we describe the existence of two mammalian glucosamine-6-phosphate deaminase enzymes. We present the crystallographic structure of one of them, the long human glucosamine-6-phosphate deaminase, at 1.75 A resolution. Crystals belong to the space group P2(1)2(1)2(1) and present a whole hexamer in the asymmetric unit. The active-site lid (residues 162-182) presented significant structural differences among monomers. Interestingly the region with the largest differences, when compared with the Escherichia coli homologue, was found to be close to the active site. These structural differences can be related to the kinetic and allosteric properties of both mammalian enzymes.
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Affiliation(s)
- Rodrigo Arreola
- Instituto de Biotecnología, Universidad Nacional Autónoma de México, PO Box 510-3, Cuernavaca, 62250 Morelos, Mexico.
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22
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Abstract
Chemically modified cytochrome c with poly(ethylene glycol) (PEG) showed activity at temperatures higher than 100 degrees C and to be highly thermostable. The molecular size of PEG moieties and the coupling site affected the thermal stabilization. An optimal PEG/protein mass ratio of 2.8 was found, producing a fully thermostable biocatalyst at 80 degrees C. Site-directed mutagenesis on yeast cytochrome c showed an increased thermostabilization when lysine 79 residue, localized at the edge of the active site, was replaced by a nonreactive residue. Tertiary, secondary, and active-site structures were analyzed by fluorescence, CD, and UV/visible spectroscopies. Besides its disordered structure, the pegylated protein showed a lower unfolding rate at the active-site than the unmodified ones. A shell-like structure seems to protect the heme environment, in which PEG is coiled on the protein surface with a primary shield of rigid water molecules solvating the hydrophilic region of bound-PEG, and the PEG hydrophobic regions interacting with the hydrophobic clusters on protein surface.
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Abstract
As the number of industrial applications for proteins continues to expand, the exploitation of protein engineering becomes critical. It is predicted that protein engineering can generate enzymes with new catalytic properties and create desirable, high-value, products at lower production costs. Peroxidases are ubiquitous enzymes that catalyze a variety of oxygen-transfer reactions and are thus potentially useful for industrial and biomedical applications. However, peroxidases are unstable and are readily inactivated by their substrate, hydrogen peroxide. Researchers rely on the powerful tools of molecular biology to improve the stability of these enzymes, either by protecting residues sensitive to oxidation or by devising more efficient intramolecular pathways for free-radical allocation. Here, we discuss the catalytic cycle of peroxidases and the mechanism of the suicide inactivation process to establish a broad knowledge base for future rational protein engineering.
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Affiliation(s)
- Brenda Valderrama
- Instituto de Biotecnología, Universidad Nacional Autónoma de México, AP 510-3 Cuernavaca, Morelos 62250, México.
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24
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Castillo A, Taboada H, Mendoza A, Valderrama B, Encarnación S, Mora J. Role of GOGAT in carbon and nitrogen partitioning in Rhizobium etli. Microbiology (Reading) 2000; 146 ( Pt 7):1627-1637. [PMID: 10878127 DOI: 10.1099/00221287-146-7-1627] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The isolation and characterization of a Rhizobium etli glutamate auxotroph, TAD12, harbouring a single Tn5 insertion, is reported. This mutant produced no detectable glutamate synthase (GOGAT) activity. The cloning and physical characterization of a 7.2 kb fragment of R. etli DNA harbouring the structural genes gltB and gltD encoding the two GOGAT subunits GltB and GltD is also reported. In comparison with the wild-type strain (CFN42), the GOGAT mutant strain utilized less succinate and glutamate and grew less with this and other amino acids as nitrogen source. R. etli assimilates ammonium by the glutamine synthetase (GS)-GOGAT pathway and a GOGAT mutant prevents the cycling of glutamine by this pathway, something that impairs nitrogen and carbon metabolism and explains the decrease in the amino-nitrogen during exponential growth, with glutamate as nitrogen source. GOGAT activity also has a role in ammonium turnover and in the synthesis of amino acids and proteins, processes that are necessary to sustain cell viability in non-growing conditions. The assimilation of ammonium is important during symbiosis and glutamate constitutes 20-40% of the total amino-nitrogen. In symbiosis, the blockage of ammonium assimilation by a GOGAT mutation significantly decreases the amino-nitrogen pool of the bacteroids and may explain why more N(2) is fixed in ammonium, excreted to the plant cell, transported to the leaves and stored in the seeds.
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Affiliation(s)
- Adriana Castillo
- Centro de Investigación sobre Fijación de Nitrógeno, Programa de Ingenierı́a Metabólica, Universidad Nacional Autónoma de México, AP 565-A, Cuernavaca, Morelos, 62271, Mexico1
| | - Hermenegildo Taboada
- Centro de Investigación sobre Fijación de Nitrógeno, Programa de Ingenierı́a Metabólica, Universidad Nacional Autónoma de México, AP 565-A, Cuernavaca, Morelos, 62271, Mexico1
| | - Alberto Mendoza
- Centro de Investigación sobre Fijación de Nitrógeno, Programa de Ingenierı́a Metabólica, Universidad Nacional Autónoma de México, AP 565-A, Cuernavaca, Morelos, 62271, Mexico1
| | - Brenda Valderrama
- Centro de Investigación sobre Fijación de Nitrógeno, Programa de Ingenierı́a Metabólica, Universidad Nacional Autónoma de México, AP 565-A, Cuernavaca, Morelos, 62271, Mexico1
| | - Sergio Encarnación
- Centro de Investigación sobre Fijación de Nitrógeno, Programa de Ingenierı́a Metabólica, Universidad Nacional Autónoma de México, AP 565-A, Cuernavaca, Morelos, 62271, Mexico1
| | - Jaime Mora
- Centro de Investigación sobre Fijación de Nitrógeno, Programa de Ingenierı́a Metabólica, Universidad Nacional Autónoma de México, AP 565-A, Cuernavaca, Morelos, 62271, Mexico1
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25
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Grande RA, Valderrama B, Morett E. Suppression analysis of positive control mutants of NifA reveals two overlapping promoters for Klebsiella pneumoniae rpoN. J Mol Biol 1999; 294:291-8. [PMID: 10610758 DOI: 10.1006/jmbi.1999.3232] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Activation of gene expression relies on direct molecular interactions between the RNA polymerase and transcription factors. Eubacterial enhancer-binding proteins (EBPs) activate transcription by binding to distant sites and, simultaneously, contacting the sigma(54)-holoenzyme form of the RNA polymerase (Esigma(54)). The interaction between the EBP and Esigma(54) is transient, such that it has been difficult to be studied biochemically. Therefore, the details of this molecular recognition event are not known. Genetic and physical evidences suggest that the highly conserved C3 region in the activation domain of the EBP has major determinants for positive control and for the interaction with Esigma(54). To further investigate the target of this region we searched for extragenic suppressors of some C3 region mutant derivatives of NifA. As a first step we mutagenized Klebsiella pneumoniae rpoN, the gene that codes for sigma(54). A mutant allele, rpoN1320, that suppressed two different NifA derivatives was obtained. Immunodetection of sigma(54) and transcriptional initiation studies demonstrated that the cause of the suppression was an enhanced expression of rpoN. A single point mutation was responsible for the phenotype. It mapped at the -10 region of an unidentified promoter, here denominated rpoNp1, and increased its similarity to the consensus. A second upstream promoter, denominated rpoNp2, was also identified. Its -10 region partially overlaps with the -35 region of rpoNp1. Interestingly, the promoter-up -10 mutation in rpoNp1 caused a reduction in the expression from rpoNp2, likely reflecting a stronger occupancy of the former promoter by the RNA polymerase at the expense of the latter. The presence of two overlapping promoters competing for the RNA polymerase implies a complex regulatory pattern that needs elucidation. The fact that increasing the concentration of sigma(54) in the cell can suppress positive control mutants of NifA adds further evidence for their direct interaction in the activation process.
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Affiliation(s)
- R A Grande
- Universidad Nacional Autónoma de México, Cuernavaca, Morelos, AP 510-3, México
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26
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Abstract
Promoters recognized by the RNA-polymerase with the alternative sigma factor sigma(54) (Esigma54) are unique in having conserved positions around -24 and -12 nucleotides upstream from the transcriptional start site, instead of the typical -35 and -10 boxes. Here we compile 186 -24/-12 promoter sequences reported in the literature and generate an updated and extended consensus sequence. The use of the extended consensus increases the probability of identifying genuine -24/-12 promoters. The effect of several reported mutations at the -24/-12 elements on RNA-polymerase binding and promoter strength is discussed in the light of the updated consensus.
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Affiliation(s)
- H Barrios
- Departamento de Reconocimiento Molecular y Bioestructura, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62271, México
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Mendoza A, Valderrama B, Leija A, Mora J. NifA-dependent expression of glutamate dehydrogenase in Rhizobium etli modifies nitrogen partitioning during symbiosis. Mol Plant Microbe Interact 1998; 11:83-90. [PMID: 9450332 DOI: 10.1094/mpmi.1998.11.2.83] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Constitutive expression of foreign glutamate dehydrogenase in Rhizobium etli inhibits bean plant nodulation (A. Mendoza, A. Leija, E. Martínez-Romero, G. Hernández, and J. Mora. Mol. Plant-Microbe Interact. 8:584-592, 1995). Here we report that this inhibition is overcome when controlling gdhA expression by NifA, thus delaying the GDH activity onset after nodule establishment. Expression of gdhA modifies the nitrogen partitioning inside the bacteroid, where newly synthesized ammonia is preferentially incorporated into the amino acid pool instead of being exported to the infected cells. As a consequence, the fixed nitrogen transport to the leaves, measured as the ureides content in xylem sap, is significantly reduced. Nitrogenase activity, although not nifHDK expression, is significantly reduced in bacteroids expressing gdhA, probably due to the utilization of energy and reducing power for nitrogen assimilation. Here we show that ammonia assimilation inside R. etli bacteroids is active, albeit at low levels, and when enhanced is deleterious to the symbiotic performance. This leads us to believe that further reduction of the basal nitrogen metabolism in the bacteroid might stimulate the nitrogenase activity and increase the nitrogen supply to the plant.
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Affiliation(s)
- A Mendoza
- Departamento de Ecología Molecular, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México.
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28
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Girard L, Valderrama B, Palacios R, Romero D, Davila G. Transcriptional activity of the symbiotic plasmid of Rhizobium etli is affected by different environmental conditions. Microbiology (Reading) 1996. [DOI: 10.1099/13500872-142-10-2847] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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29
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Valderrama B, Dávalos A, Girard L, Morett E, Mora J. Regulatory proteins and cis-acting elements involved in the transcriptional control of Rhizobium etli reiterated nifH genes. J Bacteriol 1996; 178:3119-26. [PMID: 8655489 PMCID: PMC178061 DOI: 10.1128/jb.178.11.3119-3126.1996] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
In Rhizobium etli the nitrogenase reductase genes are reiterated. Strain CE3 has three copies; nifHa and nifHb form part of nifHDK operons with the nitrogenase structural genes, while nifHc is linked to a truncated nifD homolog. Their sequences are identical up to 6 residues upstream from a sigma54-dependent promoter. A remarkable difference among them is the absence of canonical NifA binding sites upstream of nifHc while a canonical binding site is located 200 bp upstream of nifHa and nifHb. To evaluate the transcriptional regulation of the reiterated nifH genes, we constructed fusions of nifHa and nifHc with the lacZ gene of Escherichia coli. Both genes were expressed at maximum levels under 1% oxygen in free-living cultures, and their expression declined as the oxygen concentration was increased. This expression was dependent on the integrity of nifA, and nifHc was expressed at higher levels than nifHa. The same pattern was observed with root nodule bacteroids. Expression of both genes in E. coli required sigma54 in addition to NifA bound to the upstream activator sequence. In vivo dimethyl sulfate footprinting analyses showed that NifA binds to the canonical site upstream of nifHa and to a TGT half-site 6 nucleotides further upstream. NifA protected an imperfect binding site upstream of nijHc at position 85 from the promoter. The integration host factor stimulated each gene differently, nifHa being more dependent on this protein. The above results correlate the asymmetric arrangement of cis-acting elements with a differential expression of the reiterated nifH genes, both in culture and during symbiosis with bean plants.
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Affiliation(s)
- B Valderrama
- Departmento de Ecología Molecular, Centro de Investigación sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos
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