Harry M. Williams

Congrats Dan!

As usual, there's a lot more cool stuff in this paper so naturally I encourage you to have a look! Thanks of course go to the entire team at EPFL, including the wonderful people at the DCI-Lausanne imaging centre who helped us collect something a lot of data.

At 13.3 ms, we observe ErNaR in the O2 state. The chromophore has switched back to the all-trans configuration. We find the sidechain environment in the active center is starting to re-form. There also appears to be conformational dynamics taking place downstream along the proposed ion path.

At 107 µs after photoactivation, we observe the K2 state. As we show, the chromophore has switched from the all-trans configuration present in the dark state to the 13-cis configuration. A switch that is accompanied by sidechain movements around the chromophore in the ErNaR active center.

Samples of ErNaR were activated with a nanosecond laser pulse and subsequently jet vitrified at 107 µs and 13.3 ms, to probe the K2 and O2 states of the photo-cycle, respectively. We also collected a dark state, which was not photo-activated, to serve as a control in our experiments.

Next, to demonstrate that we could conduct time-resolved cryo-EM experiments, we turned to the bacterial rhodopsin ErNaR. Normally, ErNaR pumps sodium ions from the cytoplasm across the bacterial membrane to the ouside. Using our setup, we wanted to probe some of the earlier photocycle states.

To demonstrate this setup, we first prepared a sample of mouse heavy chain apoferritin. After the usual data collection and processing, we obtained a 1.3 Å volume demonstrating that we can produce high-quality cryo-samples. The volume for this is shown higher up in this thread (with sidechains).

You can see these "timing lasers" and the "time of arrival laser" (or as I prefer to call it, the bouncy laser) working together here! In this video, the jet would normally come from the right hand side whereas the activation laser would be fired from the left hand side.

We also have a "time of arrival laser". Informally, we call this the "bouncy laser" because it continuously bounces off the back-side of a grid during an experiment. When the jet reaches the grid, this laser is deflected and this gives us the actual time of arrival of the jet.

In other words, if we are interested in observing dynamics at 1 ms post-activation, we will fire the activation laser -1 ms before the predicted time of arrival of the cryogen jet. Simples!

Using this predicted time of arrival, we then fire the activation laser as the appropriate delay, which activates protein dynamics either by releasing a photoactive compound (e.g. caged-ATP) or exciting a photoactive component within a protein itself (as we demonstrate in this paper).

You can see these lasers in the first figure of this thread and can be divided into two. First, we have two "timing lasers", which detect the progress of the jet as it moves towards the grid. These allow us to calculate on-the-fly the predicted time of arrival of the jet at the grid.

We also took high-speed video frames of a similar jet and you can see these in the figure here. Now, a big part of our experiments is time. We want to accurately and precisely arrest protein dynamics at given timepoints to observe biological phenomena. To do this, we use a combination of lasers.

Here you can see the the cryogen jet traveling towards the grid, ultimately striking the grid and, in doing so, arresting protein dynamics.

To conduct a time-resolved experiment, a sample grid is placed in the activation subunit of the jetting assembly, and protein dynamics are initiated with a laser pulse. The sample is then vitrified with a liquid ethane (or ethane/propane) jet that is generated in the jetting subunit.

Experimental concept: protein dynamics are initiated with a short laser pulse. As they unfold, the sample is vitrified with a time-delayed jet of a liquid cryogen, trapping the proteins in their transient configurations.

Happy to see our latest work online. Here we present a new method for microsecond time-resolved cryo-EM based on jet vitrification! Details in the 🧵 below... we hope you enjoy reading! (Hint, there's some fun videos...) #cryoEM #structuralbiology

Always a good feeling!

MISO: microfluidic protein isolation enables single-particle cryo-EM structure determination from a single cell colony.

Or from a single dish of HEK cell culture in the case of two membrane proteins.

Out in Nature Methods now! lnkd.in/gpyBSceg

Wonderful collaboration with the Efremov lab.

We are pleased to announce Doppio version 1.4! Available here www.ccpem.ac.uk/software/dow...

Huzzah!

Hopefully leading to one or two new microscopes in Utrecht?

Our new preprint is out 🥳🥳🥳

Henipaviruses, like Nipah and Hendra, package their genomes inside helical shells built by thousands of nucleoproteins. These nucleocapsids are essential to protect the viral RNA, but how do they ever let the polymerase in to read the sequence?

👇

warwick.ac.uk/fac/cross_fa...

I am advertising for a PhD position in my group. We'll be investigating how pathogenic RNA viruses replicate in the nucleus. The project will teach cryoEM/ET, virus culture, and in vitro assays.

If you're interested reach out and I'd be happy to have a chat.

Finally, just about 2 years after finishing the postdoc the last part of my work is finally online! We determined the structure of HSV-1 Origin Binding Protein, the viral initiator of DNA replication, by cryo-EM 🧪🧬🧶🧵 #cryoEM #structuralbiology

Chris Russo and Anastasiia Gusach have developed a new method to prepare #cryoEM samples that avoids protein damage during freezing

Read more: www2.mrc-lmb.cam.ac.uk/a-new-method...

#LMBResearch

An efficient eukaryotic cell-free expression and correlative cryo-electron tomography platform for structural biology of macromolecular complexes www.biorxiv.org/content/10.1101/2025.10.18.683253v1 #cryoEM

The EPFL/UNIL sheep appear to be thoroughly enjoying the slow move into autumn.

This is very cool!

The Starbucks people know me by name, I think this counts as settling in a new place, right?