Hi all,

It’s Biophysics Week! This means that I am going to be writing about some awesome biophysics topics on my blog this week. The timing is perfect; just a month ago I attended the Biophysical Society meeting in San Francisco and have fresh material to report in these posts.

Let’s kick it off with circadian rhythms. You have probably heard this term before; the Nobel Prize in physiology and medicine in 2017 was awarded to scientists who studied the details of circadian rhythms. For those of you who aren’t familiar with it, this is just a fancy way of saying that our body has an internal clock. This clock exists so that we can adjust to the day and night cycles of the Earth. Want to test it? Mess up your sleep cycle for a couple of days, and you will see how your body gets confused about when to eat or when to sleep. The best example of this is the ‘jet lag’ we experience after traveling across continents when the external clock changes but the internal one doesn’t.

Anyway, humans, animals, plants all keep this internal clock. But even bacteria possess this biological clock, as I recently found out at the Biophysical Society meeting, and that is the topic of this post.

So, the tiny clocks inside these cyanobacteria consist of three main protein players: KaiA, KaiB, and KaiC. The research team extracted these proteins by opening up the bacterial cells and watched them at work in a test tube. They wanted to see the structures of these proteins and how they change over time. The method that they used to look at protein structures is called nuclear magnetic resonance (NMR). It is very similar to an MRI machine in hospitals. A huge magnet revealed the positions of different atoms inside the proteins and using this information the researchers could figure out the structures and interactions between the proteins.

What they observed can be best explained using a LEGO analogy: Imagine KaiA, KaiB, and KaiC to be LEGO pieces that change their shape periodically. During the day, KaiC’s shape is such that KaiA fits into it perfectly. This interaction signals the bacteria to produce daytime proteins: ones that break down sugar to produce energy. At night, KaiC changes its shape such that KaiA no longer perfectly fits in it, but KaiB does. This induces night-time proteins: ones that are involved in cell division.

Curious to know more? Check out this detailed but simplified article about this study that I wrote for Biotechniques. Also, here’s a great explainer video from the lab, which is quite easy to follow.

If you are intrigued and want to know more details about these tiny circadian clocks, you can read the original publication here: Tseng, Roger, et al. “Structural basis of the day-night transition in a bacterial circadian clock.” Science 355.6330 (2017): 1174-1180.