Sorry, again, that’s all complete and utter nonsense what Ann Gauger writes there. It was NOT a bifunctional enzyme to begin with. It was NOT a promiscuous enzyme used to begin the experiment. ONLY after multiple spontaneous mutations in the hisA gene could it catalyze BOTH reactions.
They did NOT start with a promiscuous enzyme capable of doing both reactions. They started with a His+ capable enzyme (hisA) in an organism lacking the TrpF enzyme, and selected for the presence of Trp+ function in the hisA gene. But because they knew that mutations for Trp+ in hisA genes typically eradicate the His+ function, histidine was included in the agar.
They plated bacteria lacking the ability to make tryptophan on agar containing histidine but not tryptophan, so only if a spontaneous mutant occurred capable of Trp+ would colonies form. They kept doing this until such colonies were observed. They found that initially, as expected, the hisA mutants capable of growth on medium lacking tryptophan but containing histidine have lost their His+ activity.
They then selected these Trp+ colonies for further plating and selection experiments(meaning they cultured the picked colonies for a time so they had more bacteria with spontaneous mutations to plate with) and kept plating them for a time looking for new mutants. But this time they plated on agar lacking both histidine and tryptophan, so if a colony should form, it would be from a spontaneous mutant capable of both His+ and Trp+. Such colonies were detected, meaning such spontaneous mutations in fact occurred. Nobody forced the requisite mutations to occur or “engineered” them. What was provided was the means to detect them (by a colony forming on agar), so they could be selected for further experiments. That’s it.
Nobody made the mutations come into existence. They merely set up an environment that would make it possible for them to detect when and if the requisite mutations they were interested in, occurred, by plating bacteria on plates lacking particular substrates. If a colony is observed on such a plate, it means the bacteria have evolved some way to make the substrate themselves. Unless of course it’s God intervening in the experiment, but I hear he’s stopped doing that and all his interventions are relegated to the ancient geological past and he refuses to do test-tube interventions. Must be a kind of social contract I guess.
There was no promiscuous enzyme to begin with, and a promiscuous enzyme was not created, it evolved by spontaneous mutation by plating bacteria on agar lacking the nutrients the researchers wanted to see if the bacteria were capable of evolving the ability to biosynthesize. And they were.
Sure, but this is not what happened. What happened here is something you say CAN’T happen.
This HisA Trp F conversion is something we would say could happen.
No it isn’t. You have an entire paper dedicated to arguing that this can’t possibly take place by evolution:
Gauger AK, Axe DD (2011) The evolutionary accessibility of new enzyme functions : a case study from the biotin pathway. BIO-Complexity 2011(1):1-17.
In this paper you take two highly divergent, non-promiscuous enzymes , fail to convert the function of one into the function of the other by intelligently picking residues from one and replacing the aligned corresponding amino acids in the other. After you fail converting the function of A to the function of B by rational design, you amazingly conclude evolution couldn’t ever be expected to perform a conversion of one enzyme function into another even closely related one.
So now that a multifunctional enzyme has been evolved from a single-function one by spontaneous mutation and selection by plating on agar lacking particular substrates, you are trying to spin it as a case of intelligent design. Amazingly.
When it fails (for two proteins with ~280 amino acid differences out of about 400), it means evolution is effectively impossible and ID is required, and when it succeeds (for two proteins differing by 4-6 amino acids), that’s a success of ID and couldn’t have happened by evolution.
C’mon.
Edit: for some spelling/grammar.