Ice-nucleation protein InaZ

Booking photographs

The suspect, from its real atomic coordinates. Drag to turn it. Height chart in nanometers, ruled every 1 nm. As tall as 40 unit cells of ice, stacked. Mugshot: an AlphaFold model, minus its loose N-terminal end.

Rap sheet

Answers to

InaZ, of the leaf bacterium Pseudomonas syringae.

Height

30 nm, standing on end: a rod of 61 coils.

Weight

197 zeptograms, all 1,200 amino acids.

Build

Threonine rows down one face that seem to line water up like ice.

Habits

Frosts leaves at −2 °C so its bacterium can feed.

Known for

The best ice-maker known. Tiny drops of water alone can stay liquid to −38 °C.

Suspected

Of seeding snow and hail. Most of fresh snow’s warmest ice-makers are biological.

First seen

In 1974: bacteria from rotting alder leaves froze water at −1.8 °C.

Last seen

On a leaf, on the outside of a bacterium, waiting for frost.

of them, by weight, in one ice-making site that works at −2 °C, by one estimate.
You’ve never seen one.