Scientists have acquired a more dynamic picture of events that underlie the functions of a bacterial biological clock. New research published online March 13th by Cell Press in the journal Molecular Cell, shows how the simplest organism known to have a circadian clock keeps time and may enhance our understanding of how other organisms establish and govern chronological rhythms.
A variety of organisms have evolved endogenous timing systems called a circadian clock that allows them to regulate metabolic activities in a day/night cycle. The simplest organisms known to possess a circadian oscillator are the cyanobacteria, better known as blue-green algae. The essential components of the circadian oscillator in cyanobacteria are the three clock proteins KaiA, KaiB and KaiC, all of which are expressed in the cyanobacterium S. elongatus.
Considerable research has implicated the phosphorylation cycle of KaiC as the central pacemaker in cyanobacteria and has demonstrated that the Kai proteins are repeatedly assembled and disassembled into heteromultimeric complexes, termed periodosomes. The crystal structure of each clock protein has also been determined and analyzed.
“Despite the substantial progress in structural characterization, the relationship between the assembly/disassembly dynamics and the circadian phosphorylation of KaiC is still poorly understood, mainly because of the difficulty in unraveling the underlying mechanisms solely from the static molecular pictures of individual clock components,” explains Dr. Akiyama from the Japan Science and Technology Agency.
To obtain a more complete visualization of the cyanobacterial circadian oscillator, Dr. Akiyama and colleagues used small-angle X-ray scattering (SAXS) to follow the assembly/disassembly dynamics of the S. elongatus heteromultimeric Kai complexes in real time. The researchers found that the assembly/disassembly processes are crucial for phase entrainment in the early synchronizing stage but are passively driven by the phosphorylation status of KaiC in the late oscillatory stage. Further, KaiA and KaiB are recruited to KaiC in a phosphorylation-dependent manner.
“Our findings demonstrate that the initial phase of the cyanobacterial oscillator is determined predominantly by the assembly/disassembly communication of the clock components, and that the period is essentially resistant to intracellular noise such as collisions, cytoplasmic viscosity and crowding. These resistances are achieved in the binary and ternary complexes by recruiting KaiA homodimers, KaiB homotetramers and KaiC homohexamers in a phosphorylation-dependent manner,” concludes Dr. Akiyama.
Source: Cell Press
Related stories:
Researchers better understand biological clock
Researchers at Harvard University and the Howard Hughes Medical Institute (HHMI) have discovered that a simple circadian clock found in some bacteria operates by the rhythmic addition and subtraction of phosphate groups at two key locations on a single protein. This phosphate pattern is influenced by two other proteins, driving phosphorylation to oscillate according to a remarkably accurate 24-hour cycle.
Simplest circadian clocks operate via orderly phosphate transfers
Researchers at Harvard University and the Howard Hughes Medical Institute have found that a simple circadian clock found in some bacteria operates by the rhythmic addition and subtraction of phosphate groups at two key locations on a single protein. This phosphate pattern is influenced by two other proteins, driving phosphorylation to oscillate according to a remarkably accurate 24-hour cycle.
A mammalian clock protein responds directly to light
We all know that light effects the growth and development of plants, but what effect does light have on humans and animals? A new paper by Nathalie Hoang et al., published in
PLoS Biology this week, explores this question by examining cryptochromes in flies, mice, and humans. In plants, cryptochromes are photoreceptor proteins which absorb and process blue light for functions such as growth, seedling development, and leaf and stem expansion.
Molecular basis and regulation of circadian rhythms in plants
Dr. C. Robertson McClung and his colleagues are investigating the genetic basis and molecular mechanisms of circadian cycling and regulation in plants. Dr. McClung, of the Department of Biological Sciences, Dartmouth College, will be presenting this work at the President's symposium of the annual meeting of the American Society of Plant Biologists in Mérida, Mexico.
Lack of fragile X and related gene fractures sleep
Lack of both the fragile X syndrome gene and one that is related could account for sleep problems associated with the disorder, which is the common cause of inherited mental impairment, said a consortium of researchers led by scientists at Baylor College of Medicine in Houston. Their findings appear in a report in the current issue of the
American Journal of Human Genetics.
Perfect Vision But Blind To Light
Mammals have two types of light-sensitive detectors in the retina. Known as rod and cone cells, they are both necessary to picture their environment. However, researchers at the Salk Institute for Biological Studies have found that eliminating a third sensor — cells expressing a photopigment called melanopsin that measures the intensity of incoming light —makes the circadian clock blind to light, yet leaves normal vision intact.
Circadian math: 1 plus 1 doesn't always equal 2
Like a wristwatch that needs to be wound daily for accurate time-telling, the human circadian system — the biological cycles that repeat approximately every 24 hours — requires daily light exposure to the eye's retina to remain synchronized with the solar day. In a new study published in the June issue of
Neuroscience Letters, researchers have demonstrated that when it comes to the circadian system, not all light exposure is created equal.
Study identifies food-related clock in the brain
In investigating the intricacies of the body’s biological rhythms, scientists at Beth Israel Deaconess Medical Center (BIDMC) have discovered the existence of a “food-related clock” which can supersede the “light-based” master clock that serves as the body’s primary timekeeper.