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posted by hubie on Wednesday November 27, @12:26AM   Printer-friendly
from the why-cant-we-be-ambidextrous? dept.

NASA is reporting on research concerning the chirality of amino acids and how they may have impacted the development of life here on Earth, and perhaps, elsewhere.

From the NASA Article:

The mystery of why life uses molecules with specific orientations has deepened with a NASA-funded discovery that RNA — a key molecule thought to have potentially held the instructions for life before DNA emerged — can favor making the building blocks of proteins in either the left-hand or the right-hand orientation. Resolving this mystery could provide clues to the origin of life. The findings appear in research recently published in Nature Communications.

Proteins are the workhorse molecules of life, used in everything from structures like hair to enzymes (catalysts that speed up or regulate chemical reactions). Just as the 26 letters of the alphabet are arranged in limitless combinations to make words, life uses 20 different amino acid building blocks in a huge variety of arrangements to make millions of different proteins. Some amino acid molecules can be built in two ways, such that mirror-image versions exist, like your hands, and life uses the left-handed variety of these amino acids. Although life based on right-handed amino acids would presumably work fine, the two mirror images are rarely mixed in biology, a characteristic of life called homochirality. It is a mystery to scientists why life chose the left-handed variety over the right-handed one.

DNA (deoxyribonucleic acid) is the molecule that holds the instructions for building and running a living organism. However, DNA is complex and specialized; it "subcontracts" the work of reading the instructions to RNA (ribonucleic acid) molecules and building proteins to ribosome molecules. DNA's specialization and complexity lead scientists to think that something simpler should have preceded it billions of years ago during the early evolution of life. A leading candidate for this is RNA, which can both store genetic information and build proteins. The hypothesis that RNA may have preceded DNA is called the "RNA world" hypothesis.

If the RNA world proposition is correct, then perhaps something about RNA caused it to favor building left-handed proteins over right-handed ones. However, the new work did not support this idea, deepening the mystery of why life went with left-handed proteins.

In the experiment, the researchers simulated what could have been early-Earth conditions of the RNA world. They incubated a solution containing ribozymes and amino acid precursors to see the relative percentages of the right-handed and left-handed amino acid, phenylalanine, that it would help produce.
[...]
"The findings suggest that life's eventual homochirality might not be a result of chemical determinism but could have emerged through later evolutionary pressures," said co-author Alberto Vázquez-Salazar, a UCLA postdoctoral scholar and member of Chen's research group.
[...]
"Understanding the chemical properties of life helps us know what to look for in our search for life across the solar system," said co-author Jason Dworkin, senior scientist for astrobiology at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and director of Goddard's Astrobiology Analytical Laboratory.

Dworkin is the project scientist on NASA's OSIRIS-REx mission, which extracted samples from the asteroid Bennu and delivered them to Earth last year for further study.

"We are analyzing OSIRIS-REx samples for the chirality (handedness) of individual amino acids, and in the future, samples from Mars will also be tested in laboratories for evidence of life including ribozymes and proteins," said Dworkin.

Journal Reference: Kenchel, J., Vázquez-Salazar, A., Wells, R. et al. Prebiotic chiral transfer from self-aminoacylating ribozymes may favor either handedness. Nat Commun 15, 7980 (2024). https://doi.org/10.1038/s41467-024-52362-x


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  • (Score: 1) by shrewdsheep on Wednesday November 27, @08:51AM (1 child)

    by shrewdsheep (5215) on Wednesday November 27, @08:51AM (#1383543)

    A reasonable hypothesis ... But there isn't evidence (yet) to support it. Hence the research.

    Well, it has Occam on its side. There is full symmetry between opposite chiral worlds, so the default assumption has to be chance. I think the deeper question looked at here is whether chirality of DNA/RNA translates through to chirality of amino acids. Given that there is a level of abstraction in between (tRNA), such an expectation is rather peculiar.

    Even if they would have found a connection, that would certainly not answer questions about the origin of life. Valid basic research, but over-hyped in terms of publication prominence (a lower ranked journal would have been more appropriate) and journalistic presentation, IMHO.

  • (Score: 3, Insightful) by NotSanguine on Thursday November 28, @05:37PM

    Well, it has Occam on its side.

    A fair point.

    And while random chance could certainly play a role, it seems unlikely that's the whole story.

    Why? Because chirality isn't an *exact* mirror image [wikipedia.org] in biological contexts. If that were the case you wouldn't see stuff like:

    Carvone, a terpenoid found in essential oils, smells like mint in its L-form and caraway in its R-form.[8]: 494 [verification needed] Limonene tastes like citrus when right-handed and pine when left-handed.[9]: 168 

    Homochirality also affects the response to drugs. Thalidomide, in its left-handed form, cures morning sickness; in its right-handed form, it causes birth defects.[9]: 168

    It's a mystery. And one that makes the wonderful and endlessly fascinating complexity of biology even more so!

    --
    No, no, you're not thinking; you're just being logical. --Niels Bohr