Novel selenoprotein neighborhoods suggest specialized biochemical processes

Next-generation DNA sequencing and assembly of metagenome-assembled genomes (MAGs) for uncultured species of various microbiomes adds a vast "dark matter" of hard-to-decipher protein sequences. Selenoproteins, optimized by natural selection to encode selenocysteine where cysteine might have been encoded much more easily, carry a strong clue to their function-some specialized aspect of binding or catalysis. Operons with multiple adjacent, but otherwise unrelated, selenoproteins should provide even more vivid information. In this study, efforts in protein family construction and curation, aimed at improving the PGAP genome annotation pipeline, generated multiple novel selenoprotein-containing genomic contexts that may lead to the future characterization of several systems of proteins. Past observations suggest roles in the metabolic handling of trace elements (mercury, tungsten, arsenic, etc.) or of organic compounds refractory to simpler enzymatic pathways. In addition, the work significantly expands the truth set of validated selenoproteins, which should aid future, more automated genome mining efforts.