Journal:IUCrJ:S2052252519005761

Room-temperature photo-induced martensitic transformation in a protein crystal

Steven Dajnowicz, Patricia S. Langan, Kevin L. Weiss, Ilia N. Ivanov, and Andrey Kovalevsky ^[1]

Molecular Tour
Martensitic transformations are the first-order crystal-to-crystal phase transitions that occur mostly in materials such as steel, alloys and ceramics, but are rare in molecular crystals and have not been detected in protein crystals. We discovered that crystals of a reversibly switchable fluorescent protein Tetdron can undergo the martensitic transformation by illumination with 400 nm light at room temperature. The phase transition results in the protein in crystallo tetramerization coupled to the chromophore deprotonation and substantial changes in the crystal packing as demonstrated by X-ray photocrystallography and spectroscopic measurements. The remarkable property of Tetdron crystals to undergo the photo-induced martensitic transformation can be explored to create novel martensitic biomaterials such as biomachines for biomedical applications, in which a protein molecule would play a role of a tiny molecular nanomachine to produce work. Tetdron may also find applications in future data storage devices with extreme capacities since 1 petabits of data can theoretically be written inside a Tetdron crystal measuring only 1 mm on a side.

Crystal packing in Tetdron showing a super cell along the b axis. (A) Tetdron in the equilibrium state with a single asymmetric unit below. (B) Tetramers of the 400 nm irradiated Tetdron that form within the same asymmetric unit (blue) and with neighbouring asymmetric unit (blue and green). Red boxes indicate the molecules that were used to generate the images shown immediately under the super cells.

• Tetdron in the equilibrium state with a single asymmetric unit.
• Tetramers of the 400 nm irradiated Tetdron that form within the same asymmetric unit (blue).

Structure of Tetdron in the equilibrium state:

• Entire view.
• Close-up of the chromophore (in green) site with surrounding residues.
• The chromophore in the trans configuration for Tetdron at equilibrium.

Tetdron in the “off-state” after 400 nm irradiation:

• Entire view.
• Close-up of the chromophore (in deepskyblue) site with surrounding residues.
• The chromophore in the trans configuration for Tetdron after 400 nm irradiation.

Interestingly, no structural changes near the chromophore are observed when comparing the equilibrium structure with that of the 400nm-irradiated crystal.

PDB references: dTetdron at equilibrium, 6myb; hTetdron at equilibrium, 6mxw; 400nm irradiated dTetdron, 6myc.

References

1. ↑ Dajnowicz S, Langan PS, Weiss KL, Ivanov IN, Kovalevsky A. Room-temperature photo-induced martensitic transformation in a protein crystal. IUCrJ. 2019 May 22;6(Pt 4):619-629. doi: 10.1107/S2052252519005761. eCollection, 2019 Jul 1. PMID:31316806 doi:http://dx.doi.org/10.1107/S2052252519005761