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[♪ INTRO]
The shape and function of tiny things like molecules
depend on how atoms are arranged, spaced, and linked to one another.
For example, if atoms aren’t properly arranged,
proteins in your body might not work.
And ordinary things like moving or blinking would take ages because some
proteins are responsible for speeding up reactions,
like those involved in our bodies' movement.
So, pretty darn important.
And knowing how those atoms come together and interact with
proteins is something that we owe to a scientist from
Aotearoa, New Zealand named June Sutor.
In the early 1960s, Sutor was a crystallographer,
and she studied how atoms are arranged in proteins by crystallizing them.
Crystallization is the process where things like proteins
get together into a more organized form called a crystal.
Their atoms are usually in a symmetrical 3D arrangement called a lattice.
And these crystals can be analyzed in different ways,
but Sutor specialized in a branch of crystallography called X-ray crystallography.
This is where scientists decode the shape and structure of a
protein inside the crystal by beaming X-rays through it.
Then, they can measure how the X-rays were bent after going through the crystal.
In Sutor’s time, this was done by placing the crystal in the middle of the X-ray
beam path and surrounding it with photo paper,
which was wrapped like a tube around the crystal.
When the X-rays hit the crystal, the beam gets scattered and
makes a pattern of tiny spots on the photo paper called a diffraction pattern.
Different diffraction patterns are captured by moving the crystal around at different
angles and changing the photo paper each time the crystal is moved.
Kind of similar to taking pictures of different angles of your face.
Scientists then compile the photos of the diffraction patterns to extract
information about the protein inside the crystal and build a 3D model.
Basically, it’s like if you took all those different pictures of your face and gave them
to someone else - they’d have a better idea of what your 3D
face actually looks like than if you just took one selfie.
With the 3D model, scientists can look at how close atoms are to one another in
the protein and draw conclusions.
Like if atoms are close to each other in the model,
that signals that they’re interacting with each other.
And proteins are held together by all sorts of interactions, like hydrogen bonds.
Atoms in this interaction have the ability to pull a
cloud of electrons from another atom, like hydrogen, closer to itself.
A property called electronegativity.
So, hydrogen bonds are formed because the electronegativity difference
between the interacting pair is high.
This interaction makes the “pulling atom” partially negatively charged
and the atom being pulled partially positive - and opposites attract.
Hydrogen bonds are usually formed between a molecule that contains a
hydrogen atom and another molecule with atoms like
fluorine, oxygen, or nitrogen which are very electronegative.
With less electronegative atoms, like carbon, there’s not so much
pulling or being pulled to create the positive and negative attraction,
so you wouldn’t expect them to form a pairing.
But, that’s what Sutor found out.
She discovered that the not-so-electronegative carbon
could get involved in forming hydrogen bonds.
And the reason this discovery was such a big deal it’s because it went
against what chemists traditionally knew about hydrogen bonds between atoms.
Other scientists hypothesized that this could happen, but
Sutor was the first to actually show it.
Sutor measured the distances between those atoms by using the
Van der Waals radii, which are defined as half of the distance between
two close, non-bonded atoms.
She first looked at the structure of theacrine, a chemical similar to caffeine.
The previous estimates of the Van der Waals radii in this molecule between the
carbon-hydrogen atoms and the oxygen atom were about 3.40 angstroms.
Scientists didn’t expect there to be any hydrogen bonds
between the carbon and the hydrogen because of the similarity in electronegativity.
But using crystallography and calculations,
Sutor found that it was, in fact, just three angstroms.
A shorter distance meant the carbon-hydrogen
in the molecule was doing more pulling.
So, the carbon was helping form a hydrogen bond with the oxygen.
Across her published work, she had multiple examples,
including molecules like DNA.
Which showed that this kind of special hydrogen bond is
found in lots of places in nature, particularly in proteins.
Where lots of these types of attractions help give the protein its shape.
But despite all the evidence Sutor provided, her work was discredited at the
time and may have never seen the light of day.
She received fierce scientific opposition from another
crystallographer named Jerry Donohue.
Now, we’re all for retesting and disputing people’s findings;
that’s what scientific rigor is all about!
The problem was just how much sway Donohue
had and the way he went about the critique.
He was pretty much the authority on the topic at the time.
He even helped Watson and Crick analyze fellow
crystallographer Rosalind Franklin’s stolen DNA work.
And instead of publishing his critiques in an academic journal,
he wrote them in a book that ended up sitting on the shelves
of every crystallography laboratory in the UK.
By the time the book came out, Sutor had moved on to other work and later
returned home to Aotearoa New Zealand, so she didn’t respond to the critiques.
But her redemption came in 1982 when chemists Robin Taylor and Olga Kennard
published a paper with lots more evidence that backed Sutor’s findings.
Then in 1996, a famous crystallographer, Gautam Desiraju,
dedicated a scientific paper to acknowledge her contributions to the field.
But sadly, Sutor’s name is still pretty unknown in the scientific world,
even though her work forms the basis for
understanding and building protein models today.
But with this episode, we’re celebrating her achievements as a
way to say thank you for all her amazing work.
And if you want to take a deeper dive into all biology has to offer,
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If you liked today’s episode you should check their course on “Computational Biology”
where they take you on a back-of-the-envelope approach to teach you how computers
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