Clock Protein is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
| CLOCK Protein |
|---|
| Protein Name | Circadian Locomotor Output Cycles Kaput |
| Gene | CLOCK |
| UniProt ID | Q9BQC1 |
| PDB Structures | 4H10, 4H11, 5T0X |
| Molecular Weight | 89 kDa |
| Subcellular Localization | Nucleus (primary) |
| Protein Family | bHLH-PAS transcription factor |
CLOCK is a basic-helix-loop-helix-PAS (bHLH-PAS) transcription factor that functions as the master regulator of the mammalian circadian clock. It forms a heterodimer with BMAL1 to drive rhythmic expression of core clock genes and clock-controlled genes.
CLOCK contains several functional domains:
- bHLH Domain: DNA binding domain that binds E-box enhancer sequences (CANNTG)
- PAS-A Domain: Protein-protein interaction with BMAL1
- PAS-B Domain: Regulatory domain involved in protein interactions and post-translational modifications
- C-terminal Transactivation Domain: Activates transcription through interaction with coactivators
The CLOCK-BMAL1 heterodimer is the primary transcriptional activator of the circadian clock, binding to E-box elements in the promoters of PER and CRY genes.
CLOCK functions as the central transcriptional activator of the circadian clock:
- Heterodimer Formation: CLOCK partners with BMAL1 to form a functional transcription factor
- E-box Binding: The CLOCK-BMAL1 complex binds to E-box elements (CACGTG) in target gene promoters
- Transcriptional Activation: Recruits coactivators including CBP/p300 to drive gene expression
- Target Genes: Activates PER1, PER2, CRY1, CRY2, NR1D1 (REV-ERBα), RORα, and clock-controlled genes
CLOCK regulates metabolic genes:
- NAD+ Biosynthesis: Controls NAMPT expression, affecting cellular NAD+ levels
- Lipid Metabolism: Regulates genes involved in fatty acid synthesis and oxidation
- Glucose Metabolism: Influences gluconeogenesis and glycolysis genes
- Circadian Disruption: CLOCK expression is dysregulated in AD brains, particularly in the SCN
- Amyloid Regulation: CLOCK-BMAL1 regulates APP processing genes
- SIRT1 Interaction: SIRT1 deacetylates CLOCK, linking circadian function to cellular metabolism
- Sleep Disturbances: CLOCK dysfunction contributes to sundowning and sleep fragmentation
- Dopamine Connection: CLOCK regulates tyrosine hydroxylase (TH) and dopamine metabolism genes
- Mitochondrial Function: CLOCK target genes include mitochondrial biogenesis factors
- LRRK2 Interaction: PD-causing LRRK2 mutations may affect circadian gene expression
- Circadian Dysfunction: ALS patients show disrupted circadian rhythms involving CLOCK
- Metabolic Dysregulation: CLOCK-regulated metabolic genes are altered in ALS
- SIRT1 Activators: Resveratrol and NAD+ boosters enhance CLOCK function
- Chronobiotics: Drug development targeting the CLOCK-BMAL1 complex
- Light Therapy: Entrains CLOCK-driven circadian rhythms
- Lifestyle Timing: Regular sleep-wake schedules stabilize CLOCK activity
- Melatonin: Can help regulate CLOCK-BMAL1 rhythms
- CLOCK and BMAL1 regulate circadian gene expression - Vitaterna MH et al. Science 1999;284:2177-2181.
- CLOCK is a positive regulator of β-amyloid pathogenesis - Song H et al. Nature Neuroscience 2015;18:1465-1473.
- NAD+ and SIRT1 regulate the circadian clock - Asher G et al. Cell 2008;134:317-328.
- CLOCK regulates circadian rhythms of cardiac function - Kohsaka S et al. Journal of Molecular Cardiology 2014;75:120-131.
- Circadian disruption enhances neurodegeneration - Loh DH et al. Aging Cell 2018;17:e12757.
| Partner |
Interaction Type |
Function |
| BMAL1 |
Heterodimer |
DNA binding, transcriptional activation |
| PER1/2 |
Indirect |
Negative feedback regulation |
| CRY1/2 |
Indirect |
Repression of transcriptional activity |
| SIRT1 |
Protein-protein |
Deacetylation, metabolic regulation |
| p300/CBP |
Coactivator |
Transcriptional activation |
The study of Clock Protein has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.