RESUMEN
Electronic connection between Qo and Qi quinone catalytic sites of dimeric cytochrome bc1 is a central feature of the energy-conserving Q cycle. While both the intra- and inter-monomer electron transfers were shown to connect the sites in the enzyme, mechanistic and physiological significance of the latter remains unclear. Here, using a series of mutated hybrid cytochrome bc1-like complexes, we show that inter-monomer electron transfer robustly sustains the function of the enzyme in vivo, even when the two subunits in a dimer come from different species. This indicates that minimal requirement for bioenergetic efficiency is to provide a chain of cofactors for uncompromised electron flux between the catalytic sites, while the details of protein scaffold are secondary.
Asunto(s)
Proteínas Bacterianas/química , Proteínas Bacterianas/metabolismo , Complejo III de Transporte de Electrones/química , Complejo III de Transporte de Electrones/metabolismo , Rhodobacter capsulatus/enzimología , Proteínas Bacterianas/genética , Transporte de Electrón , Complejo III de Transporte de Electrones/genética , Genes Bacterianos , Modelos Moleculares , Proteínas Mutantes/química , Proteínas Mutantes/genética , Proteínas Mutantes/metabolismo , Procesos Fototróficos , Conformación Proteica , Proteínas Recombinantes de Fusión/química , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismo , Rhodobacter capsulatus/genética , Rhodobacter capsulatus/crecimiento & desarrolloRESUMEN
Intracellular folate homeostasis and metabolism is regulated by numerous genes. Among them, 5,10-methylenetetrahydrofolate reductase (MTHFR) is of special interest because of its involvement in regulation of the homocysteine level in the body as a result of folate metabolism. Moreover, some studies demonstrated that the homocysteine plasma level in individuals may be influenced by polymorphisms present in the MTHFR gene. Two common, clinically relevant mutations have been described: MTHFR C677T and MTHFR A1298C. Although several laboratory techniques allow genotyping of both polymorphisms, PCR-RFLP analysis is simple to perform, relatively cheap, and thus one of the most utilized. In the case of A1298C, the PCR-RFLP technique that utilizes MboII endonuclease class II requires an acrylamide gel electrophoresis, since agarose gel electrophoresis is unable to resolve short deoxyribonucleic acid (DNA) fragments after restriction digestion. Agarose gel electrophoresis is commonly preferred over that of acrylamide. To resolve this inconvenience, a novel PCR-RFLP, AjuI-based method to genotype A1298C alleles has been developed that can be performed on standard agarose gel.
Asunto(s)
Metilenotetrahidrofolato Reductasa (NADPH2)/genética , Biología Molecular/métodos , Mutación Missense/genética , Reacción en Cadena de la Polimerasa/métodos , Polimorfismo de Longitud del Fragmento de Restricción/genética , Secuencia de Bases , Genotipo , Humanos , Datos de Secuencia MolecularRESUMEN
To address mechanistic questions about the functioning of dimeric cytochrome bc1 new genetic approaches have recently been developed. They were specifically designed to enable construction of asymmetrically-mutated variants suitable for functional studies. One approach exploited a fusion of two cytochromes b that replaced the separate subunits in the dimer. The fusion protein, built from two copies of the same cytochrome b of purple bacterium Rhodobacter capsulatus, served as a template to create a series of asymmetrically-mutated cytochrome bc1-like complexes (B-B) which, through kinetic studies, disclosed several important principles of dimer engineering. Here, we report on construction of another fusion protein complex that adds a new tool to investigate dimeric function of the enzyme through the asymmetrically mutated forms of the protein. This complex (BS-B) contains a hybrid protein that combines two different cytochromes b: one coming from R. capsulatus and the other - from a closely related species, R. sphaeroides. With this new fusion we addressed a still controversial issue of electron transfer between the two hemes bL in the core of dimer. Kinetic data obtained with a series of BS-B variants provided new evidence confirming the previously reported observations that electron transfer between those two hemes occurs on a millisecond timescale, thus is a catalytically-relevant event. Both types of the fusion complexes (B-B and BS-B) consistently implicate that the heme-bL-bL bridge forms an electronic connection available for inter-monomer electron transfer in cytochrome bc1.
Asunto(s)
Citocromos b/química , Complejo III de Transporte de Electrones/química , Hemo/química , Proteínas Recombinantes de Fusión/química , Rhodobacter capsulatus/enzimología , Rhodobacter sphaeroides/enzimología , Catálisis , Transporte de Electrón , LuzRESUMEN
Fusing proteins is an attractive genetic tool used in several biochemical and biophysical investigations. Within a group of redox proteins, certain fusion constructs appear to provide valuable templates for spectroscopy with which specific bioenergetic questions can be addressed. Here we briefly summarize three different cases of fusions reported for bacterial cytochrome bc(1) (prokaryotic equivalent of mitochondrial respiratory complex III), a common component of electron transport chains. These fusions were used to study supramolecular organization of enzymatic complexes in bioenergetic membrane, influence of the accessory subunits on the activity and stability of the complex, and molecular mechanism of operation of the enzyme in the context of its dimeric structure. Besides direct connotation to molecular bioenergetics, these fusions also appeared interesting from the protein design, biogenesis, and assembly points of view. This article is part of a Special Issue entitled: 17th European Bioenergetics Conference (EBEC 2012).
Asunto(s)
Proteínas Bacterianas , Complejo III de Transporte de Electrones , Metabolismo Energético , Proteínas Recombinantes de Fusión , Animales , Proteínas Bacterianas/química , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Complejo III de Transporte de Electrones/química , Complejo III de Transporte de Electrones/genética , Complejo III de Transporte de Electrones/metabolismo , Humanos , Ingeniería de Proteínas/métodos , Proteínas Recombinantes de Fusión/química , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismoRESUMEN
Homodimeric structure of cytochrome bc1, a common component of biological energy conversion systems, builds in four catalytic quinone oxidation/reduction sites and four chains of cofactors (branches) that, connected by a centrally located bridge, form a symmetric H-shaped electron transfer system. The mechanism of operation of this complex system is under constant debate. Here, we report on isolation and enzymatic examination of cytochrome bc1-like complexes containing fused cytochrome b subunits in which asymmetrically introduced mutations inactivated individual branches in various combinations. The structural asymmetry of those forms was confirmed spectroscopically. All the asymmetric forms corresponding to cytochrome bc1 with partial or full inactivation of one monomer retain high enzymatic activity but at the same time show a decrease in the maximum turnover rate by a factor close to 2. This strongly supports the model assuming independent operation of monomers. The cross-inactivated form corresponding to cytochrome bc1 with disabled complementary parts of each monomer retains the enzymatic activity at the level that, for the first time on isolated from membranes and purified to homogeneity preparations, demonstrates that intermonomer electron transfer through the bridge effectively sustains the enzymatic turnover. The results fully support the concept that electrons freely distribute between the four catalytic sites of a dimer and that any path connecting the catalytic sites on the opposite sides of the membrane is enzymatically competent. The possibility to examine enzymatic properties of isolated forms of asymmetric complexes constructed using the cytochrome b fusion system extends the array of tools available for investigating the engineering of dimeric cytochrome bc1 from the mechanistic and physiological perspectives.
Asunto(s)
Proteínas Bacterianas/metabolismo , Citocromos b/metabolismo , Complejo III de Transporte de Electrones/metabolismo , Subunidades de Proteína/metabolismo , Rhodobacter capsulatus/enzimología , Sustitución de Aminoácidos , Proteínas Bacterianas/química , Proteínas Bacterianas/genética , Proteínas Bacterianas/aislamiento & purificación , Biocatálisis , Dominio Catalítico , Cromatografía de Afinidad , Citocromos b/química , Citocromos b/genética , Citocromos b/aislamiento & purificación , Espectroscopía de Resonancia por Spin del Electrón , Transporte de Electrón , Complejo III de Transporte de Electrones/química , Complejo III de Transporte de Electrones/genética , Complejo III de Transporte de Electrones/aislamiento & purificación , Cinética , Modelos Moleculares , Proteínas Mutantes/química , Proteínas Mutantes/aislamiento & purificación , Proteínas Mutantes/metabolismo , Mutación Puntual , Ingeniería de Proteínas , Dominios y Motivos de Interacción de Proteínas , Multimerización de Proteína , Subunidades de Proteína/química , Subunidades de Proteína/genética , Subunidades de Proteína/aislamiento & purificación , Proteínas Recombinantes de Fusión/química , Proteínas Recombinantes de Fusión/aislamiento & purificación , Proteínas Recombinantes de Fusión/metabolismoRESUMEN
Cytochrome bc(1) (mitochondrial complex III), one of the key enzymes of biological energy conversion, is a functional homodimer in which each monomer contains three catalytic subunits: cytochrome c(1), the iron-sulfur subunit and cytochrome b. The latter is composed of eight transmembrane α-helices which, in duplicate, form a hydrophobic core of a dimer. We show that two cytochromes b can be fused into one 16-helical subunit using a number of different peptide linkers that vary in length but all connect the C-terminus of one cytochrome with the N-terminus of the other. The fusion proteins replace two cytochromes b in the dimer defining a set of available protein templates for introducing mutations that allow breaking symmetry of a dimer. A more detailed comparison of the form with the shortest, 3 amino acid, linker to the form with 12 amino acid linker established that both forms display similar level of structural plasticity to accommodate several, but not all, asymmetric patterns of mutations that knock out individual segments of cofactor chains. While the system based on a fused gene does not allow for the assessments of the functionality of electron-transfer paths in vivo, the family of proteins with fused cytochrome b offers attractive model for detailed investigations of molecular mechanism of catalysis at in vitro/reconstitution level.
Asunto(s)
Proteínas Bacterianas/metabolismo , Citocromos b/metabolismo , Ingeniería de Proteínas/métodos , Rhodobacter capsulatus/metabolismo , Secuencia de Aminoácidos , Proteínas Bacterianas/química , Proteínas Bacterianas/genética , Western Blotting , Citocromos b/química , Citocromos b/genética , Complejo III de Transporte de Electrones/química , Complejo III de Transporte de Electrones/genética , Complejo III de Transporte de Electrones/metabolismo , Modelos Moleculares , Datos de Secuencia Molecular , Mutagénesis , Multimerización de Proteína , Estructura Cuaternaria de Proteína , Proteínas Recombinantes de Fusión/química , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismo , Rhodobacter capsulatus/genética , EspectrofotometríaRESUMEN
The need of hepatitis C virus (HCV) monitoring in serum samples of infected persons is of particular importance, because of chronic and non-symptomatic disease course of hepatitis C infection. We developed a novel "in-house" method variant for the detection of HCV genetic material in human blood serum. Detection technique is based on reverse transcription-real time polymerase chain reaction (RT-rPCR). We designed and analyzed several HCV 5' UTR-complementary PCR starter and probe sequence sets and we chose one set of highest HCV detection potency. Optimal concentration of starters and probe has been found. The 226-base pair long fragment of constitutively expressed glyceraldehyde 3-phosphate dehydrogenase gene served as internal endogenous control and should be added to each analysis in order to ensure that no PCR inhibitors are present. All parameters were optimized for Mx3005 QPCR System (Agilent Technology).