Posts tagged enzyme
Articles and news from the latest research reports.
Enzyme that produces melatonin originated 500 million years ago
An international team of scientists led by National Institutes of Health researchers has traced the likely origin of the enzyme needed to manufacture the hormone melatonin to roughly 500 million years ago.
Their work indicates that this crucial enzyme, which plays an essential role in regulating the body’s internal clock, likely began its role in timekeeping when vertebrates (animals with spinal columns) diverged from their nonvertebrate ancestors.
An understanding of the enzyme’s function before and after the divergence may contribute to an understanding of such melatonin-related conditions as seasonal affective disorder, jet lag, and to the understanding of disorders involving vision.
The findings provide strong support for the theory that the time-keeping enzyme originated to remove toxic compounds from the eye and then gradually morphed into the master switch for controlling the body’s 24-hour cyclic changes in function.
The researchers isolated a second, nonvertebrate form of the enzyme from sharks and other contemporary animals thought to resemble the prototypical early vertebrates that lived 500 million years ago.
The study, published online in PNAS, was conducted by senior author David C. Klein, Ph.D., Chief of the Section on Neuroendocrinology in the NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) and colleagues at NIH, and at institutions in France, Norway, and Japan.
Melatonin is a key hormone that regulates the body’s day and night cycle. Dr. Klein explained that it is manufactured in the brain’s pineal gland and is found in small amounts in the retina of the eye. Melatonin is produced from the hormone serotonin, the end result of a multistep sequence of chemical reactions. The next-to-last step in the assembly process consists of attaching a small molecule — the acetyl group — to the nearly finished melatonin molecule. This step is performed by an enzyme called arylalkylamine N-acetyltransferase, or AANAT.
Because of its key role in producing the body clock-regulating melatonin, AANAT is often referred to as the timezyme, Dr. Klein added.
The form of AANAT found in vertebrates occurs in the brain’s pineal gland and, in small amounts, in the retina. Another form of the enzyme, termed nonvertebrate AANAT, has been found only in other forms of life, such as bacteria, plants and insects.
“Nonvertebrate AANAT appears to detoxify a broad range of potentially toxic chemicals,” Dr. Klein said. “In contrast, vertebrate AANAT is highly specialized for adding an acetyl group to melatonin. The two are as different from each another as a Ferrari is from a Model-T Ford, considering the speed of the reaction and how fast it can be turned on and off.”
In 2004, Dr. Klein and his coworkers published a theory that melatonin was at first a kind of cellular waste, a by-product created in cells of the eye when normally toxic substances were rendered harmless. Because melatonin accumulated at night, the ancestors of today’s vertebrates became dependent on melatonin as a signal of darkness. As the need for greater quantities of melatonin grew, the pineal gland developed as a structure separate from the eyes, to keep serotonin and other toxic substances needed to make melatonin away from sensitive eye tissue.
“The pineal glands of birds and reptiles can detect light,” Dr. Klein said. “And the retinas of human beings and other species also make melatonin. So it would appear that both tissues evolved from a common, ancestral, light-detecting tissue.”
Before the current study, the researchers lacked proof of their theory, particularly in regard to the question of how the vertebrate form of the enzyme originated because it did not appear to exist in non-vertebrates and had been found only in bony fishes, reptiles, birds, and mammals — all of which lacked the non-vertebrate form.
The first evidence of how the vertebrate form of the enzyme originated came when study co-author Steven L. Coon, also of NICHD, discovered genes for the nonvertebrate and vertebrate forms of AANAT in genomic sequences from the elephant shark, considered to be a living representative of early vertebrates.
This finding indicated that the vertebrate form of AANAT may have resulted after a phenomenon known as gene duplication, Dr. Klein said. Gene duplication, he added, typically results from any of a number of genetic mishaps during cell division. Instead of one copy of a gene resulting from the process, an additional copy results, so that there are two versions of a gene where only one existed previously. The phenomenon is thought to be a major factor influencing evolutionary change.
The researchers theorized that following duplication, one form of AANAT remained unchanged and the other gradually evolved into the vertebrate form. Dr. Klein said that at some point after vertebrate AANAT developed, vertebrates appear to have stopped making the nonvertebrate form, perhaps because it was no longer needed or because its function was replaced by a similar enzyme.
Before the researchers could continue, they needed to confirm their finding, to rule out that the nonvertebrate AANAT they found didn’t result from accidental contamination with bacteria or some other organism. The NICHD researchers sought assistance from other research teams around the world. DNA from Mediterranean sharks and sea lampreys was obtained via fishermen’s catches by Jack Falcon of the Arago Laboratory, a marine biology facility that is part of the CNRS and the Pierre and Marie Curie University in France. Samples from a close relative of the elephant shark — the ratfish — were provided by Even-Jorgensen at the Arctic University of Norway. Finally, Susumo Hyodo of the University of Tokyo contributed samples from elephant sharks he collected off the coast of Australia.
Next, the Hyodo and Falcon groups isolated RNA from the retinas and pineal glands of the animals. RNA is used to direct the assembly of amino acids into proteins. From these RNA sequences, it was possible to assemble working versions of AANAT molecules — both the vertebrate and nonvertebrate forms.
The sequences of the proteins encoded by the AANAT genes were analyzed by Eugene Koonin and Yuri Wolf of the National Library of Medicine using computer techniques designed to study evolution. Peter Steinbach, of NIH’s Center for Information Technology, examined the three-dimensional structures of nonvertebrate and vertebrate AANAT in the study animals and determined that the two forms of the enzyme likely had a common ancestor.
Taken together, their results provide evidence for the hypothesis that nonvertebrate AANAT resulted from duplication of the non-vertebrate AANAT gene about 500 million years ago and that following this event one copy of the duplicated gene eventually changed into the gene for vertebrate AANAT.
In addition to providing information on the origin of melatonin and the evolution of AANAT, the findings also have implications for research on disorders affecting vision. Vertebrate AANAT and melatonin are found in small amounts in the eyes of humans and other vertebrates. Although they may play a role in detoxifying compounds, it is also reasonable to consider that this detoxifying function is shared with other enzymes.
“It’s possible that a malfunction in these other enzymes might lead to an accumulation of chemicals known as arylalkamines — in the same family as serotonin — and this might contribute to eye disease,” Dr. Klein said. “Consequently, research into how these enzymes function might lead to therapies to protect vision.”
Promising compound restores memory loss and reverses symptoms of Alzheimer’s
A new ray of hope has broken through the clouded outcomes associated with Alzheimer’s disease. A new research report published in January 2013 print issue of The FASEB Journal by scientists from the National Institutes of Health shows that when a molecule called TFP5 is injected into mice with disease that is the equivalent of human Alzheimer’s, symptoms are reversed and memory is restored—without obvious toxic side effects.
"We hope that clinical trial studies in AD patients should yield an extended and a better quality of life as observed in mice upon TFP5 treatment," said Harish C. Pant, Ph.D., a senior researcher involved in the work from the Laboratory of Neurochemistry at the National Institute of Neurological Disorders at Stroke at the National Institutes of Health in Bethesda, MD. "Therefore, we suggest that TFP5 should be an effective therapeutic compound."
To make this discovery, Pant and colleagues used mice with a disease considered the equivalent of Alzheimer’s. One set of these mice were injected with the small molecule TFP5, while the other was injected with saline as placebo. The mice, after a series of intraperitoneal injections of TFP5, displayed a substantial reduction in the various disease symptoms along with restoration of memory loss. In addition, the mice receiving TFP5 injections experienced no weight loss, neurological stress (anxiety) or signs of toxicity. The disease in the placebo mice, however, progressed normally as expected. TFP5 was derived from the regulator of a key brain enzyme, called Cdk5. The over activation of Cdk5 is implicated in the formation of plaques and tangles, the major hallmark of Alzheimer’s disease.
"The next step is to find out if this molecule can have the same effects in people, and if not, to find out which molecule will," said Gerald Weissmann, M.D., Editor-in-Chief of the FASEB Journal. “Now that we know that we can target the basic molecular defects in Alzheimer’s disease, we can hope for treatments far better – and more specific – than anything we have today.”
(Source: eurekalert.org)
Key protein interactions involved in neurodegenerative disease revealed
Scientists from the Florida campus of The Scripps Research Institute (TSRI) have defined the molecular structure of an enzyme as it interacts with several proteins involved in outcomes that can influence neurodegenerative disease and insulin resistance. The enzymes in question, which play a critical role in nerve cell (neuron) survival, are among the most prized targets for drugs to treat brain disorders such as Parkinson’s disease, Alzheimer’s disease and amyotrophic lateral sclerosis (ALS).
The study was published online ahead of print on November 8, 2012, by the journal Structure.
The new study reveals the structure of a class of enzymes called c-jun-N-terminal kinases (JNK) when bound to three peptides from different protein families; JNK is an important contributor to stress-induced apoptosis (cell death), and several studies in animal models have shown that JNK inhibition protects against neurodegeneration.
"Our findings have long-range implications for drug discovery," said TSRI Professor Philip LoGrasso, who, along with TSRI Associate Professor Kendall Nettles, led the study. "Knowing the structure of JNK bound to these proteins will allow us to make novel substrate competitive inhibitors for this enzyme with even greater specificity and hopefully less toxicity."
The scientists used what they called structure class analysis, looking at groups of structures, which revealed subtle differences not apparent looking at them individually.
"From a structural point of view, these different proteins appear to be very similar, but the biochemistry shows that the results of their binding to JNK were very different," he said.
LoGrasso and his colleagues were responsible for creating and solving the crystal structures of the three peptides (JIP1, SAB, and ATF-2) with JNK3 using a technique called x-ray crystallography, while Nettles handled much of the data analysis.
All three peptides have important effects, LoGrasso said, inducing two distinct inhibitory mechanisms—one where the peptide caused the activation loop to bind directly in the ATP pocket, and another with allosteric control (that is, using a location on the protein other than the active site). Because JNK signaling needs to be tightly controlled, even small changes in it can alter a cell’s fate.
"Solving the crystal structures of these three bound peptides gives us a clearer idea of how we can block each of these mechanisms related to cell death and survival," LoGrasso said. "You have to know their structure to know how to deal with them."
(Source: medicalxpress.com)
A molecular scissor related to Alzheimer’s Disease
An international research team led by the Spanish National Research Council (CSIC) and researchers from Kiel University revealed the atomic-level structure of the human peptidase enzyme meprin ß (beta). The enzyme is related to inflammation, cancer and Alzheimer’s Disease and is involved in cellular proliferation and differentiation. The knowledge of the enzyme structure will allow for the development of a new medication type different from those known up to now. The study was published in the current issue of the journal “Proceedings of the National Academy of Sciences”.
“Now that we know how meprin ß looks, how it works and how it relates to diseases, we can search for substances that stop its enzyme activities when they become harmful”, explains Xavier Gomis-Rüth, researcher at the Molecular Biology Institute of Barcelona, who led the project. Meprin ß is an enzyme that is anchored in the outer wall of cells. Its normal function in the human metabolism is to cut off certain proteins, e.g. growth factors, that are also anchored in the cell wall. In this way meprin ß releases protein fragments into the environment surrounding the cells – a natural and normal process, as long as it occurs at a certain intensity. However, under specific circumstances, meprin ß may function abnormally, and, for example, releases too many protein fragments. The protein pieces than overdo their natural task in the cell surroundings, causing disorder in the human body. Such disorder typically occurs when inflammation, cancer or Alzheimer’s Disease get started.
Neuroscientists at New York University have devised a method that has reduced several afflictions associated with Fragile X syndrome (FXS) in laboratory mice. Their findings, which are reported in the journal Neuron, offer new possibilities for addressing FXS, the leading inherited cause of autism and intellectual disability.
Those afflicted with FXS do not possess the protein FMRP, which is a suppressor of protein synthesis. Absent this suppressor, protein synthesis is exaggerated, producing a range of mental and physical disorders.
Previous research has indirectly targeted protein synthesis by seeking to temper, but not block, this process. The NYU researchers, by contrast, sought a more fundamental intervention—removing the enzyme, p70 ribosomal S6 kinase 1, or S6K1, which has previously been shown to regulate protein synthesis in FXS mice. By addressing this phenomenon at the molecular level, they hoped to diminish many of the conditions associated with FXS.
Mayo Clinic Researchers Identify New Enzyme to Fight Alzheimer’s Disease
An enzyme that could represent a powerful new tool for combating Alzheimer’s disease has been discovered by researchers at Mayo Clinic in Florida. The enzyme — known as BACE2 — destroys beta-amyloid, a toxic protein fragment that litters the brains of patients who have the disease. The findings were published online Sept. 17 in the science journal Molecular Neurodegeneration.
Alzheimer’s disease is the most common memory disorder. It affects more that 5.5 million people in the United States. Despite the disorder’s enormous financial and personal toll, effective treatments have not yet been found.
The Mayo research team, led by Malcolm A. Leissring, Ph.D., a neuroscientist at Mayo Clinic in Florida, made the discovery by testing hundreds of enzymes for the ability to lower beta-amyloid levels. BACE2 was found to lower beta-amyloid more effectively than all other enzymes tested. The discovery is interesting because BACE2 is closely related to another enzyme, known as BACE1, involved in producing beta-amyloid.
“Despite their close similarity, the two enzymes have completely opposite effects on beta-amyloid — BACE1 giveth, while BACE2 taketh away,” Dr. Leissring says.
Beta-amyloid is a fragment of a larger protein, known as APP, and is produced by enzymes that cut APP at two places. BACE1 is the enzyme responsible for making the first cut that generates beta-amyloid. The research showed that BACE2 cuts beta-amyloid into smaller pieces, thereby destroying it, instead. Although other enzymes are known to break down beta-amyloid, BACE2 is particularly efficient at this function, the study found.
Previous work had shown that BACE2 can also lower beta-amyloid levels by a second mechanism: by cutting APP at a different spot from BACE1. BACE2 cuts in the middle of the beta-amyloid portion, which prevents beta-amyloid production.
“The fact that BACE2 can lower beta-amyloid by two distinct mechanisms makes this enzyme an especially attractive candidate for gene therapy to treat Alzheimer’s disease,” says first author Samer Abdul-Hay, Ph.D., a neuroscientist at Mayo Clinic in Florida.
The discovery suggests that impairments in BACE2 might increase the risk of Alzheimer’s disease. This is important because certain drugs in clinical use — for example, antiviral drugs used to treat human immunodeficiency virus (HIV) — work by inhibiting enzymes similar to BACE2.
Although BACE2 can lower beta-amyloid by two distinct mechanisms, only the newly discovered mechanism — beta-amyloid destruction — is likely relevant to the disease, the researchers note. This is because the second mechanism, which involves BACE2 cutting APP, does not occur in the brain. The researchers have obtained a grant from the National Institutes of Health to study whether blocking beta-amyloid destruction by BACE2 can increase the risk for Alzheimer’s disease in a mouse model of the disease.
(Source: newswise.com)