Metalloenzymes and Molecular Bioenergetics
Metalloproteins and Bioenergetics Unit
The main research themes of the Laboratory are the study at the molecular level of the structure and functional mechanisms of soluble and membrane-bound metalloenzymes, namely those involved in oxygen and nitric oxide metabolisms.
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Miguel Sepúlveda Teixeira (ID)
The appearance of oxygen in the atmosphere ca 2.5 Gy ago introduced a huge challenge for life, on what became known as the oxygen paradox: oxygen, when directly reduced to water by respiratory enzymes, namely the heme-copper oxygen reductases, allows energy conservation and, indeed, allows to extract maximal energy from the reduced organic compounds; on the other hand, if reduction of oxygen occurs stepwise, in a non-controlled way, leads to the formation of reactive oxygen species, such as the superoxide anion or hydrogen peroxide.
In this laboratory we study metalloenzymes involved in both aspects of oxygen biochemistry. We aim at contributing to the understanding of the molecular mechanisms of membrane-bound heme-copper oxygen reductases, namely of the processes whereby these enzymes couple oxygen reduction to the translocation of protons across the membrane.These studies have been focused on one enzyme of each of the three types, A-C, in order to have a global understanding of the essential features of the mechanism. On the other side, we have been studying in detail, using wt and mutant enzymes, the mechanism of superoxide reduction by the 1Fe and 2Fe superoxide reductases, in particular by coupling pulse radiolysis to very fast (microseconds) electronic absorption measurements. We proposed a catalytic mechanism that involved the formation of a ferric-hydroperoxo species, which decays, in some enzymes, through a ferric hydroxide to the final, ferric resting state; in other enzymes, the ferric hydroperoxo decays directly to the ferric resting state. The three dimensional studies of several of these enzymes have been determined, in different forms, in collaboration with the ITQB Macromolecular Crystallography Unit. The other enzymes under study, more recently, are those endowed with hydrogen peroxide reductase activity. These enzymes contain a di-iron site, where the reaction takes place, but the molecular mechanism remains to be established, and is one of our aims. Again, the 3D structure of one of these enzymes has already been obtained.
Finally, another major project in the Laboratory is the study of the flavodiiron proteins, which have oxygen and/or nitric oxide reductase activities. Our present objectives are twofold: establish the molecular mechanism of the reaction and understand what dictates the preference towards O2 or NO.
These objectives, as well as other more specific, have been accomplished in collaboration with several groups at ITQB, and in particular within the Metalloproteins and Bioenergetics Unit.
- Célia Romão, Auxiliary Investigator (with Structural Genomics, Macromolecular Crystallography Unit)
- Ana P. Batista, Post-doc (with Biological Energy Transduction, Metalloproteins and Bioenergetics Unit)
- Patrícia N. Refojo, Post-doc (with Biological Energy Transduction, Metalloproteins and Bioenergetics Unit)
- Sandra I. Santos, PhD student
- Vera L. Gonçalves, PhD student (with Molecular Genetics of Microbial Resistance)
- Cecília Miranda, BI Research student (with Structural Genomics, Macromolecular Crystallography Unit)
- Miguel A. Ribeiro, BI Research student
- Rodrigo David, Master student
- Diana Cruz, Master student
- Joana Carrilho, Undergraduate student
- Liliana Pinto, Technician
- Desulforubrerythrin from Campylobacter jejuni, a novel multidomain protein Pinto, A. F, Todorovic, S, Hildebrandt, P, Yamazaki, M, Amano, F ., Igimi, S , Romao, CV , Teixeira, M Journal of Biological Inorganic Chemistry, 2011, 16, 501-51
- The superoxide reductase from the early diverging eukaryote Giardia intestinalis Testa, F, Mastronicola, D., Cabelli, D. E. , Bordi, E., Pucillo, L. P, Sarti, P., Saraiva, L. M, Giuffre, A., Teixeira, M.Free Radical Biology and Medicine, (2011), 51, 1567-157
- Pinto, A.F., Rodrigues, J.V. and Teixeira M. (2010), Reductive elimination of superoxide: Structure and mechanism of superoxide reductases. Biochim Biophys Acta. 1804, 285-297.
For further information please visit the laboratory's website
O aparecimento do oxigénio há cerca de 2.5 Giga anos introduziu um enorme desafio para os seres vivos, naquilo que se desihna geralmente o paradox do oxigénio: o oxigénio, quando reduzido directamente a água pelas enzimas respiratórias, em particular as oxigénio reductases de hemo-cobre, permite a conservação de energia e, de facto, esta redução permite a extracção mais eficiente da energia dos compostos orgânicos solúveis; por outro lado, se a redução do oxigénio ocorrer passo a passo, de modo não controlado, formam-se espécies reactivas de oxigénio, como o anião superóxido e o peróxido de hidrogénio, bastante prejudiciais a todos os seres vivos.
Neste Laboratório estudam-se metaloenzimas envolvidas nos dois aspectos da bioquímica do oxigénio: as oxigénio-reductases de hemo-cobre, membranares, e as reductases de oxigénio, superóxido e peróxido de hidrogénio, citoplasmáticas.