Game Over? Nick Lane Wants Another Inning
David Coppedge
The score is 36-0, but the Darwin Team isn’t ready to concede. Lehigh University biochemist Michael Behe, writing for World Magazine (see our coverage here), described how he attended a conference of scientists to hear Nobel laureate John E. Walker, the world’s expert on ATP synthase, explain how it might have evolved. To design advocates, this rotary engine is a paragon of intelligent design. Walker, who shared a Nobel Prize for elucidating the motor’s rotary mechanism, spent his whole time describing the intricacies of this molecular machine, and never offered an evolutionary explanation for it until the Q&A session. Then, he was asked directly how a mindless process could produce such a stunning piece of work. Walker stumbled, offering only a fragment of speculation that it must have arisen “Slowly, through some sort of intermediate or other.” That’s when Behe, out of earshot, muttered two simple words, “Game over.”
Game over. The losing team heads for the showers with heads bowed. The Darwin Team’s MVP had just struck out at the bottom of the ninth. Calling the game in such an obvious wipeout would have been superfluous. The crowds file out of the stands. Suddenly, eight players run onto the field! “Wait! Wait!” they cry. “Let us have a time at bat!”
The rescue team, led by Nick Lane of University College London, waves a paper over their heads. It’s hot off the press from PLOS Biology, titled, “A prebiotic basis for ATP as the universal energy currency.” Lane shouts, We have the intermediate! It’s AcP! One of the refs eyeballs the paper for a minute. Will it be worth calling the teams back onto the field for another inning?
A Plausible Scenario?
The gist of the hypothesis is that acetyl phosphate (AcP), a simple molecule with the formula C2H5O5P, can phosphorylate ADP into ATP in water, if ferric ion (Fe3+) is present. The team believes their lab work offers a plausible scenario for prebiotic ATP formation without the need for ATP synthase.
ATP is universally conserved as the principal energy currency in cells, driving metabolism through phosphorylation and condensation reactions. Such deep conservation suggests that ATP arose at an early stage of biochemical evolution. Yet purine synthesis requires 6 phosphorylation steps linked to ATP hydrolysis.This autocatalytic requirement for ATP to synthesize ATP implies the need for an earlier prebiotic ATP equivalent, which could drive protometabolism before purine synthesis. Why this early phosphorylating agent was replaced, and specifically with ATP rather than other nucleoside triphosphates, remains a mystery. Here, we show that the deep conservation of ATP might reflect its prebiotic chemistry in relation to another universally conserved intermediate, acetyl phosphate (AcP), which bridges between thioester and phosphate metabolism by linking acetyl CoA to the substrate-level phosphorylation of ADP. We confirm earlier results showing that AcP can phosphorylate ADP to ATP at nearly 20% yield in water in the presence of Fe3+ions. We then show that Fe3+ and AcP are surprisingly favoured.
Sounds Impressive. Can It Work?
The team tells the referee about additional surprising benefits of their intermediate. Visions of the Miller spark apparatus come to mind:
Surprisingly, our results demonstrate that maximal ATP synthesis occurred at high water activity and low ion concentrations, indicating that prebiotic ATP synthesis would be most feasible in freshwater systems.Likewise, ferrous iron can be oxidized to ferric iron by photochemical reactions or oxidants such as NO derived from volcanic emissions, meteorite impacts, or lightning strikes, which also points to terrestrial geothermal systems as a plausible environment for aqueous ATP synthesis.
Questions & Answers
powers a disequilibrium in the ratio of ADP to ATP, which amounts to 10 orders of magnitude from equilibrium in the cytosol of modern cells. Molecular engines such as the ATP synthase use ratchet-like mechanical mechanisms to convert environmental redox disequilibria into a highly skewed ratio of ADP to ATP.” But we cannot say how that happened.
But how could a simple prebiotic system composed mostly of monomers sustain a disequilibrium in ATP to ADP ratio that powers work? Well, “One possibility is that dynamic environments could sustain critical disequilibria across short distances such as protocell membranes.”
Didn’t you just assume the existence of a protocell with a membrane? Where did those come from? Look, we’re not trying to come up with a complete picture of how life originated. We’re just trying to explain why ATP is the universal energy currency for life as it exists today, and how it might have emerged.
Emerged… by chance, you mean? Isn’t that circular reasoning? How so? What other possibility is there?
There’s intelligence, the only cause ever observed that is capable of assembling complex parts into a functional whole. Sorry; we thought this was a scientific baseball diamond.
It is. So what is your explanation for the functional information in the simplest life? Your paper admits that “ATP links energy metabolism with genetic information.” What is the source of that genetic information? Uh, some sort of intermediate or other.
The referees convene and shout out, “GAME OVER!”
