Chloroplast f and m Thioredoxins Discovered in Nonphotosynthet...( ROCKVILLE MD -- Thioredoxins (TRXs)...)

ROCKVILLE, MD -- Thioredoxins (TRXs) are a large family of small proteins that function in multiple metabolic processes in all living organisms. They are a good example of proteins that have diversified throughout evolution, probably from one ancestral protein that arose in ancient cyanobacteria. TRXs are ubiquitous cellular workhorses that can alter the catalytic properties of specific enzymes. In these so-called redox-regulated reactions, TRXs can transfer hydrogen to convert a disulfide bridge formed between two cysteine amino acids to their unbridged thiol forms. These TRX-responsive disulfide bridges have regulatory functions in numerous cellular processes, including regulatory cascades related to enzyme regulation, stress responses, DNA translation and transcription, protein folding and repair, cell death, and gene expression.

Plants have the largest number of thioredoxins of all organisms and are found in all of the major compartments of the plant cell - cytosol, mitochondria, and chloroplasts. In chloroplasts, TRXs regulate numerous enzymes involved in the transformation of carbon into sugars. They also function to regulate the photosynthetic production of ATP, the energy currency of all living organisms and in fatty acid synthesis. In a report to be published in the November issue of Plant Physiology, researchers have found that the f and m type plant thioredoxins previously thought to be localized only in chloroplasts are also found in other, nonphotosynthetic, tissues, where they may have multiple functions. A team from the laboratory of Dr. Mariam Sahrawy of the Estacin Experimental del Zaidin in Granada, Spain, established the presence of these redox proteins in tissues other than the chloroplast by fusing the promoters of these genes to a visible reporter molecule, -glucuronidase (GUS), and by expression analysis, in situ hybridization, and immunological analysis.

All the different types of plant TRXs are encoded
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