Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Monday, March 2, 2020

Proteins in space

There's always a danger, when you want to believe something really really really badly, that you'll jump to belief on the basis of questionable evidence.

It's called confirmation bias, and it plagues us all, skeptic and non-skeptic alike.  It's why I've always tried to be more critical of claims that line up with what I want to be true -- because I'm more likely to accept such arguments unquestioningly.

Well, I try to.  It was kind of hard to do when I read a paper by Malcolm McGeoch ((PLEX Corporation), Sergei Dikler (Bruker Scientific), and Julie McGeoch (Harvard Univeristy) that appeared in arXiv last Friday, with the unprepossessing name, "Hemolithin: A Meteoric Protein Containing Iron and Lithium," which you'd think would only be of interest to biochemistry nerds, but had me leaping about making excited little squeaking noises.

Maybe you've already figured out why from the title, but if not, here's the salient bit:
This paper characterizes the first protein to be discovered in a meteorite. Amino acid polymers previously observed in Acfer 086 and Allende meteorites have been further characterized in Acfer 086 via high precision MALDI mass spectrometry to reveal a principal unified structure of molecular weight 2320 Daltons that involves chains of glycine and hydroxy-glycine residues terminated by iron atoms, with additional oxygen and lithium atoms...  Analysis of the complete spectrum of isotopes associated with each molecular fragment shows 2H enhancements above terrestrial averaging 25,700 parts per thousand (sigma = 3,500, n=15), confirming extra-terrestrial origin and hence the existence of this molecule within the asteroid parent body of the CV3 meteorite class.  The molecule is tipped by an iron-oxygen-iron grouping that in other terrestrial contexts has been proposed to be capable of absorbing photons and splitting water into hydroxyl and hydrogen moieties...
Analysis via iron and lithium isotope satellites in mass spectrometry reveals a novel protein motif with iron atoms closing out the ends of anti-parallel peptide chains composed of glycine.  Very high 2H content indicates proto-solar disc or molecular cloud origin. FeO3Fe groups at each end are of a type that could split H2O upon absorption of photons.  The existence of a unique chain length suggests that there could be a functionality conferring a replication advantage.
 They found a protein in a meteorite.  An extraterrestrial protein.  An extraterrestrial protein that appears to be able to perform photolysis -- the fracturing of water using the energy from light.

Like, the first step in photosynthesis in plants.

That was the point when my jaw hit the floor.

One of the barriers to estimating the likelihood of extraterrestrial life is that we don't know how common it is for planets to have conditions supporting a biochemistry.  I say "a" biochemistry because there's no particular necessity that extraterrestrial life have the same chemistry we do.  It's long been speculated, for example, that there could be a biochemistry based upon silicon, which (like carbon) has four valence electrons and is capable of bonding into chains, sheets, and rings.  Like many of us, I first ran into this idea with the episode of Star Trek called "The Devil in the Dark" -- where the intrepid space travelers of the U. S. S. Enterprise were confronted with a life form that used silicon instead of carbon as a biochemical scaffolding, and hydrofluoric acid instead of water as a solvent and carrier -- and so initially, it didn't look alive at all, more like some kind of extremely caustic rock.


Here, though, we don't even need to go as way out as silicon-based life.  Here we have a protein based on amino acids found right here on Earth -- glycine and hydroxyglycine -- coupled with attachment to metal ions, much like many terrestrial proteins (hemoglobin being the obvious example).  If the conditions for biochemical reactions to produce such a protein can be achieved in a proto-solar disc or molecular cloud -- as McGeoch et al. claim -- then carbon-based biochemistry, and probably life, might be a lot more common in the universe than we thought.

On the other hand...

The really far-fetched I-Want-To-Believe streak in me has to wonder if the mysterious protein they found isn't an indication that complex biochemicals can form easily and under a great variety of conditions, but an indication of life.

Like, this protein was produced by a living thing, somewhere out there.

I find it extremely suggestive that the meteoric protein looks like it has the same ability as the photosystem-II array in chloroplasts -- using light to break apart water.  In plants this frees electrons that then are used to store chemical energy as ATP and ultimately synthesize glucose, and therefore underpin virtually every energy-demanding reaction in every life form on Earth.  If I had to pick the one reaction that was the most central to the survival of every terrestrial life form, that'd be it.

The discovery of such a protein in a meteorite is somewhere in that rarified environment just past "mind-blowing."

I'm trying to control myself, here.  I know it's easy to leap to the conclusion that this is evidence of extraterrestrial life, or at the very least, that life is all over the place out there in space.  At the moment, we just have a single bit of protein in a single meteorite.

But it's an alien protein.  One that has a function that, even in the careful diction of the scientists who discovered it, would give it a replication advantage.

Okay, I need to stop writing now, because I feel another bout of jumping around making excited squeaking noises coming on.

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This week's Skeptophilia book-of-the-week is brand new -- science journalist Lydia Denworth's brilliant and insightful book Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond.

Denworth looks at the evolutionary basis of our ability to form bonds of friendship -- comparing our capacity to that of other social primates, such as a group of monkeys in a sanctuary in Puerto Rico and a tribe of baboons in Kenya.  Our need for social bonds other than those of mating and pair-bonding is deep in our brains and in our genes, and the evidence is compelling that the strongest correlate to depression is social isolation.

Friendship examines social bonding not only from the standpoint of observational psychology, but from the perspective of neuroscience.  We have neurochemical systems in place -- mediated predominantly by oxytocin, dopamine, and endorphin -- that are specifically devoted to strengthening those bonds.

Denworth's book is both scientifically fascinating and also reassuringly optimistic -- stressing to the reader that we're built to be cooperative.  Something that we could all do with a reminder of during these fractious times.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]





1 comment:

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