Structures of myxobacterial phytochrome revealed by cryo-EM using the Spotiton technique and with x-ray crystallography
Category
Published on
Type
journal-article
Author
Prabin Karki and David Menendez and William Budell and Shishir Dangi and Carolina Hernandez and Joshua Mendez and Srinivasan Muniyappan and Shibom Basu and Peter Schwander and Tek N. Malla and Emina A. Stojković and Marius Schmidt
Citation
Karki, P., Menendez, D., Budell, W., Dangi, S., Hernandez, C., Mendez, J., Muniyappan, S., Basu, S., Schwander, P., Malla, T. N., Stojković, E. A., & Schmidt, M. (2025). Structures of myxobacterial phytochrome revealed by cryo-EM using the Spotiton technique and with x-ray crystallography. Structural Dynamics, 12(3). https://doi.org/10.1063/4.0000301
Abstract
Phytochromes are red-light photoreceptors first identified in plants, with homologs found in bacteria and fungi, that regulate a variety of critical physiological processes. They undergo a reversible photocycle between two distinct states: a red-light-absorbing Pr form and a far-red light-absorbing Pfr form. This Pr/Pfr photoconversion controls the activity of a C-terminal enzymatic domain, typically a histidine kinase (HK). However, the molecular mechanisms underlying light-induced regulation of HK activity in bacteria remain poorly understood, as only a few structures of unmodified bacterial phytochromes with HK activity are known. Recently, cryo-EM structures of a wild-type bacterial phytochrome with HK activity are solved that reveal homodimers in both the Pr and Pfr states, as well as a heterodimer with individual monomers in distinct Pr and Pfr states. Cryo-EM structures of a truncated version of the same phytochrome—lacking the HK domain—also show a homodimer in the Pfr state and a Pr/Pfr heterodimer. Here, we describe in detail how structural information is obtained from cryo-EM data on a full-length intact bacteriophytochrome, and how the cryo-EM structure can contribute to the understanding of the function of the phytochrome. In addition, we compare the cryo-EM structure to an unusual x-ray structure that is obtained from a fragmented full-length phytochrome crystallized in the Pr-state.
