Jose Castresana

Cytochrome oxidase evolved by tinkering with denitrification enzymes

The cytochrome bc complex which is encoded by the fixNOPQ operon in Bradyrhizobiumjaponicum, is the most distant member of the haem‐copper cytochrome oxidase family. We have found that its major subunit, FixN, is homologous to the NorB subunit of nitric oxide reductase in a purple bacterium. A second evolutionary link between cytochrome oxidases and denitrification enzymes is the presence of a similar binuclear copper site in cytochrome aa 3 (the mitochondrial oxidase) and nitrous oxide reductase. This centre was probably acquired by a primitive FixN‐type oxidase, leading to the evolution of the mitochondrial‐type oxidase. These links suggest that the oxygen‐reducing respiratory chain developed from the anaerobic, denitrifying respiratory system.

Evolution of cytochrome oxidase, an enzyme older than atmospheric oxygen.

Cytochrome oxidase is a key enzyme in aerobic metabolism. All the recorded eubacterial (domain Bacteria) and archaebacterial (Archaea) sequences of subunits 1 and 2 of this protein complex have been used for a comprehensive evolutionary analysis. The phylogenetic trees reveal several processes of gene duplication. Some of these are ancient, having occurred in the common ancestor of Bacteria and Archaea, whereas others have occurred in specific lines of Bacteria. We show that eubacterial quinol oxidase was derived from cytochrome c oxidase in Gram‐positive bacteria and that archaebacterial quinol oxidase has an independent origin. A considerable amount of evidence suggests that Proteobacteria (Purple bacteria) acquired quinol oxidase through a lateral gene transfer from Gram‐positive bacteria. The prevalent hypothesis that aerobic metabolism arose several times in evolution after oxygenic photosynthesis, is not sustained by two aspects of the molecular data. First, cytochrome oxidase was present in the common ancestor of Archaea and Bacteria whereas oxygenic photosynthesis appeared in Bacteria. Second, an extant cytochrome oxidase in nitrogen‐fixing bacteria shows that aerobic metabolism is possible in an environment with a very low level of oxygen, such as the root nodules of leguminous plants. Therefore, we propose that aerobic metabolism in organisms with cytochrome oxidase has a monophyletic and ancient origin, prior to the appearance of eubacterial oxygenic photosynthetic organisms.

Does Vav bind to F-actin through a CH domain?

An actin‐binding protein domain we call here ‘calponin‐homology’ or CH is present in signalling proteins such as Vav which are involved in activation and inactivation of small G‐proteins. Using profile methods, we have detected two repeats of this domain in the actin‐binding region of α‐actinin and related proteins. Based on this, we propose that CH domain in Vav and other signalling proteins is employed for association with filamentous actin, and that this function correlates with their control on the G‐proteins Rac and Rho which are involved in the organization of cytoskeleton.

Nitric oxide reductases in bacteria.

Nitric oxide reductases (NORs) that are found in bacteria belong to the large enzyme family which includes cytochrome oxidases. Two types of bacterial NORs have been characterised. One is a cytochrome bc-type complex (cNOR) that receives electrons from soluble redox protein donors, whereas the other type (qNOR) lacks the cytochrome c component and uses quinol as the electron donor. The latter enzyme is present in several pathogens that are not denitrifiers. We summarise the current knowledge on bacterial NORs, and discuss the evolutionary relationship between them and cytochrome oxidases in this review.

Evolution of energetic metabolism: the respiration-early hypothesis

The main energy-transducing metabolic systems originated and diversified very early in the evolution of life. This makes it difficult to unravel the precise steps in the evolution of the proteins involved in these processes. Recent molecular data suggest that homologous proteins of aerobic respiratory chains can be found in Bacteria and Archaea, which points to a common ancestor that possessed these proteins. Other molecular data predict that this ancestor was unlikely to perform oxygenic photosynthesis. This evidence, that aerobic respiration has a single origin and may have evolved before oxygen was released to the atmosphere by photosynthetic organisms, is contrary to the textbook viewpoint.

Terminal Oxidases of Sulfolobus: Genes and Proteins

Summary The genes encoding the two terminal oxidases of Sulfolobus acidocaldarius and their products are characterized. Both archaeal complexes, SoxABCD and SoxM, are homologous to the superfamily of haemcopper oxidases. They have unusual subunit compositions. Highly conserved sequence patterns of SoxABCD and SoxM, corresponding to the redox centre binding sites of the catalytical subunit I are compared with other oxidases of the family. Distance analysis suggests that both Sulfolobus oxidases belong to two different subgroups.