Circadian disruption influences metabolic health. Metabolism modulates circadian function. However, the mechanisms coupling circadian rhythms and metabolism remain poorly understood. Here, we report that cystathionine β‐synthase (CBS), a central enzyme in one‐carbon metabolism, functionally interacts with the core circadian protein cryptochrome 1 (CRY1). In cells, CBS augments CRY1‐mediated repression of the CLOCK/BMAL1 complex and shortens circadian period. Notably, we find that mutant CBS‐I278T protein, the most common cause of homocystinuria, does not bind CRY1 or regulate its repressor activity. Transgenic Cbs^Zn/Zn mice, while maintaining circadian locomotor activity period, exhibit reduced circadian power and increased expression of E‐BOX outputs. CBS function is reciprocally influenced by CRY1 binding. CRY1 modulates enzymatic activity of the CBS. Liver extracts from Cry1^−/− mice show reduced CBS activity that normalizes after the addition of exogenous wild‐type (WT) CRY1. Metabolomic analysis of WT, Cbs^Zn/Zn, Cry1^−/−, and Cry2^−/− samples highlights the metabolic importance of endogenous CRY1. We observed temporal variation in one‐carbon and transsulfuration pathways attributable to CRY1‐induced CBS activation. CBS‐CRY1 binding provides a post‐translational switch to modulate cellular circadian physiology and metabolic control.

The molecular circadian clock is regulated by a transcriptional translational feedback loop. However, the post-translational control mechanisms are less understood. The NRON complex is a large ribonucleoprotein complex, consisting of a lncRNA and several proteins. Components of the complex play a distinct role in regulating protein phosphorylation, synthesis, stability, and translocation in cellular processes. This includes the NFAT and the circadian clock pathway. PSMD11 is a component of the NRON complex and a lid component of the 26S proteasome. Among the PSMD family members, PSMD11 has a more specific role in circadian clock function. Here, we used cell and biochemical approaches and characterized the role of PSMD11 in regulating the stability and nuclear translocation of circadian clock proteins. We used size exclusion chromatography to enrich the NRON complex in the cytosolic and nuclear fractions. More specifically, PSMD11 knockdown affected the abundance of PER2 and CRY2 proteins and the nuclear translocation of CRY1. This changed the relative abundance of CRY1 and CRY2 in the nucleus. Thus, this work defines the role of PSMD11 in the NRON complex regulating the nuclear translocation of circadian repressors, thereby enabling cellular circadian oscillations.

Significance: We successfully identified theduperallele as a null mutation of Cryptochrome 1 in Syrian hamsters. Here, we have shown the use of fast homozygosity mapping as an effective approach to identify causal mutations in mammals, despite lacking chromosomal genome information. In the course of this work, we improved the draft Syrian hamster genome and generated datasets necessary to exploit Syrian hamsters as a modern genetic research model. The unique physiological features of Syrian hamsters make them a desirable model to investigate human diseases, including circadian disorders, cancer, heart function, metabolism, and infectious diseases (e.g., severe acute respiratory syndrome coronavirus 2).

Circadian disruption influences metabolic health. Metabolism modulates circadian function. However, the mechanisms coupling circadian rhythms and metabolism remain poorly understood. Here we report that Cystathionine β-synthase (CBS), a central enzyme in one-carbon metabolism, functionally interacts with the core circadian protein Cryptochrome1 (CRY1). In cells, CBS augments CRY1 mediated repression of the CLOCK/BMAL1 complex and shortens circadian period. Notably, we find that mutant CBS-I278T protein, the most common cause of homocystinuria, does not bind CRY1 or regulate its repressor activity. TransgenicCbs^Zn/Znmice, while maintaining circadian locomotor activity period, exhibit reduced circadian power and increased expression of E-BOX outputs. CBS function is reciprocally influenced by CRY1 binding. CRY1 modulates enzymatic activity of the CBS. Liver extracts fromCry1^−/−mice show reduced CBS activity that normalizes after the addition of exogenous wild type (WT) CRY1. Metabolomic analysis of WT,Cbs^Zn/Zn,Cry1^−/−, andCry2^−/−samples highlights the metabolic importance of endogenous CRY1. We observed temporal variation in one-carbon and transsulfuration pathways attributable to CRY1 induced CBS activation. CBS-CRY1 binding provides a post-translational switch to modulate cellular circadian physiology and metabolic control.

Circadian rhythms are conserved across a wide range of organisms, including cyanobacteria, fungi, insects, and mammals. Approximately 50% of gene transcription, 8-38% of protein translation, and 13-22% of metabolites in mice have been shown to cycle with 24-hour rhythmicity. Approximately 75% of the current medications on the market target circadian-controlled pathways. However, current drug discovery and improvement studies are far from investigating the effect of time of day. In the current study, the optimal time of day for treating Chronic Obstructive Pulmonary Disease (COPD) with salmeterol is shown based on the circadian profiles of the target proteins in the target tissues. This calculation strategy aims to provide timing guidance for the drugs targeting rhythmic pathways or being metabolised by them. The current study also reveals different predicted optimal times of day for male and female mice, highlighting the importance of gender variability in circadian studies. The approach proposed in this research could be beneficial in studies that consider the circadian timing of medications.