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Publication Abstract from PubMed

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.

Structures of myxobacterial phytochrome revealed by cryo-EM using the Spotiton technique and with x-ray crystallography.,Karki P, Menendez D, Budell W, Dangi S, Hernandez C, Mendez J, Muniyappan S, Basu S, Schwander P, Malla TN, Stojkovic EA, Schmidt M Struct Dyn. 2025 May 1;12(3):034701. doi: 10.1063/4.0000301. eCollection 2025 , May. PMID:40322674^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.