Compare and Contrast

Complete single mutagenesis in the proteinI have an exam tomorrow, so this will have to be brief. The Friday DpSU – Study Shows Proteins Cannot Evolve – is by Jeffrey Tomkins, and relates to a paper published in Nature (pdf) in early October. From my quick reading the primary experiment of the paper was to take a short protein and test the relative functionality of mutated versions of it, where one amino acid in the chain had been substituted for one of the other possibilities – repeated for every possible single substitution. What they found is what should be expected: a small portion of the possibilities had a negative effect, but the vast majority had precious little (being only slightly negative or positive). Nevertheless, Tomkins opens:

Researchers just announced the systematic laboratory induced mutation of successive amino acids over the entire sequence of a simple bacterial protein. The results showed how even the simplest of life’s proteins have irreducibly complex chemical structures. The research also showed how random evolutionary processes that are ascribed to mutations are unable to propel evolution.

This is wrong. For one, the researches tried to modify the protein to bind to something slightly different than it usually does. They found that changing only two amino acids was sufficient to accomplish this, and that if only one of those changes was made the resulting protein would bind to both the normal and the different ligand:

Such a phenotype could be evolutionarily important when a mutational path characterized by a promiscuous but biologically functional intermediate is advantageous.

In addition, I hold out hope that when he says that the research demonstrates irreducible complexity he’s making some kind of private joke. Tomkins’ argument in that regard seems to boil down to “some mutations are bad,” and that’s not sufficient evidence for the claim. Continue reading