Circadian oscillator proteins across the kingdoms of life: structural aspects

Abstract

Circadian oscillators are networks of biochemical feedback loops that generate 24-hour rhythms in organisms from bacteria to animals. These periodic rhythms result from a complex interplay among clock components that are specific to the organism, but share molecular mechanisms across kingdoms. A full understanding of these processes requires detailed knowledge, not only of the biochemical properties of clock proteins and their interactions, but also of the three-dimensional structure of clockwork components. Posttranslational modifications and protein–protein interactions have become a recent focus, in particular the complex interactions mediated by the phosphorylation of clock proteins and the formation of multimeric protein complexes that regulate clock genes at transcriptional and translational levels. This review covers the structural aspects of circadian oscillators, and serves as a primer for this exciting realm of structural biology.

Exposure to Artificial Light at Night and the Consequences for Flora, Fauna, and Ecosystems

“… Simplified schematic representation of the circadian clock in (A) mammals, (B) insects, (C) Cyanobacteria, (D) fungi, and (E) plants. For details see Saini R. et al (2019) . Abbreviations: CCA1, circadian clock associated 1; CCG, clock controlled genes; Clk, clock; CRY, cryptochrome; CYC, cycle; ELF, early flowering; FRH, FRQ-interacting RNA, helicase; FRQ, frequency; GI, gigantea; LHY, late elongated hypocotyl; LUX, lux arrhythmo; PER, period; Rev-Erbβ (orphan nuclear receptor family 1); PRR, pseudo-response regulator; RORα, retinoic acid receptor (RAR)-related orphan receptors; TIM, timeless; TOC1, timing of cab expression 1; VVD, vivid; WC, white collar; WCC, white collar complex.…”

“…The purpose here is to highlight the universality of the underlying principle as well as the wide range of situations encountered regarding the qualitative aspects of clock entrainment by light ( Bhadra et al, 2017 ; Saini R. et al, 2019 ).…”

“…Because the functioning of the clock involves similar operating mechanisms with different molecular actors, it is thought that clocks have appeared independently several times during evolution ( Pegoraro and Tauber, 2011 ). The number of these actors varies from a few (fungi, green algae) to many (plants, animals) ( Saini R. et al, 2019 ). The molecular mechanisms of the circadian clocks, have been described in detail in Cyanobacteria, fungi ( Neurospora crassa ), plants ( Arabidopsis thalliana ), green algae ( Chlamydomonas reinhardtii , Ostreococcus tauri ), insects ( Drosophila melanogaster ) and several representatives of vertebrates including human ( Tomioka and Matsumoto, 2010 , 2015 ; Ukai and Ueda, 2010 ; Nakamichi, 2011 ; Peschel and Helfrich-Forster, 2011 ; Vatine et al, 2011 ; Hurley et al, 2015 ; Ito and Tomioka, 2016 ; Koritala and Lee, 2017 ; Gil and Park, 2019 ).…”

Sleeping Sickness: A Tale of Two Clocks

“…One recent plot twist is that the protozoan parasite that disrupts the host clock has a circadian clock itself (Rijo-Ferreira et al, 2017a ). Multiple organisms across the tree of life have been described to have circadian clocks, with key aspects of the molecular mechanism identified from bacteria, fungus, plants and animals (Saini et al, 2019 ). However, prior to our work there was no concrete evidence for the existence of circadian clocks in parasitic protozoans (Rijo-Ferreira et al, 2017b ).…”

Abiotic stress through time

“…The conservation of a circadian oscillator across all domains of life is compelling evidence that keeping track of time confers a fitness advantage. The molecular components of the circadian clock in plants, animals, and bacteria are unique, suggesting their clocks evolved independently (Saini et al ., 2019). For many organisms in the green lineage, the molecular clock has retained the transcriptional‐translational feedback circuit of morning‐ and evening‐expressed activators and repressors (Box 1; Fig.…”