When it comes to building proteins, it’s in a bacterium’s own best interest to use low-cost components. After all, using an energetically expensive amino acid where a cheaper one would suffice gives your more parsimonious competitors an advantage, and prior studies prove that abundant proteins are hit hard by this selective hammer: they have disproportionately high numbers of these more economical amino acids.
A new study released by mBio shows this bacterial thriftiness doesn’t stop with the most abundant proteins. Extracellular proteins are also a target for energetic penny-pinching. Since proteins used outside the cell are eventually lost and not recycled like other cellular proteins, it pays for a cell to use the cheapest amino acids available, and a close examination of the extracellular proteins in Escherichia coli reveals they contain, on average, fewer energetically-expensive amino acids, regardless of their abundance, length, function, or structure. In silico analysis of proteins from other bacterial species confirmed the bias in favor of more economical amino acids in extracellular proteins.