Insights on how proteins evolve new functions from studying the steroid receptor family: conformational flexibility is key.
A mechanism by which stress hormones inhibit the immune system, which appeared to be relatively new in evolution, may actually be hundreds of millions of years old.
A protein called the glucocorticoid receptor or GR, which responds to the stress hormone cortisol, can take on two different forms to bind DNA: one for activating gene activity, and one for repressing it. In a paper published Dec. 28 in PNAS, scientists show how evolutionary fine-tuning has obscured the origin of GRâ€™s ability to adopt different shapes.
â€œWhat this highlights is how proteins that end up evolving new functions had those capacities, because of their flexibility, at the beginning of their evolutionary history,â€ says lead author Eric Ortlund, PhD, associate professor of biochemistry at Emory University School of Medicine.
GR is part of a family of steroid receptor proteins that control cellsâ€™ responses to hormones such as estrogen, testosterone and aldosterone. Our genomes contain separate genes encoding each one. Scientists think that this family evolved by gene duplication, branch by branch, from a single ancestor present in primitive vertebrates. Continue reading “Ancient protein flexibility may drive ‘new’ functions”
A protein critical for repairing DNA-protein cross links in yeast is a SUMO ligase, Keith Wilkinson and colleagues have revealed.
The DNA in our cells is constantly being damaged by heat, radiation and other environmental stresses, andÂ the enzyme systems that repair DNA are critical for life. A particularly toxic form of damage is the covalent attachment of a protein to DNA, which can be triggered by radiation or by anticancer drugs.
Emory biochemist Keith Wilkinson and colleagues have a paper this week in the journal eLife probing how a yeast protein called Wss1 is involved in repairing DNA-protein crosslinks. The researchers show how Wss1 wrestles with a protein tag called SUMO onÂ the site of the DNA damage, and how Wss1 and SUMO areÂ involved in the cleanup process.
Three interesting things about this paper:
*The paper grew out of first author Maxim Balakirevâ€™s sabbatical with Wilkinson at Emory. Balakirev’s home base is at the CEA (Alternative Energy and Atomic Energy Commission)Â in Grenoble, France.
* Since manyÂ cancer chemotherapy drugs induce protein-DNA cross links, an inhibitor of cross linkÂ repair could enhance those drugs’ effectiveness. On the other side of the coin, mutations in a human gene called Spartan, whose sequence looks similar to Wss1â€™s, cause premature aging and susceptibility to liver cancer. Whether the Spartan-encoded protein has the same biochemical activity as Wss1 is not yet clear.
Satiety lipid OEA may act as lysosomal signal to nucleus
The idea that particular lipid components, such as omega-3 fatty acids, promote health is quite familiar, so the finding that the lipid oleoylethanolamide or OEA extends longevity in the worm C. elegans is perhaps not so surprising. However, a recent paper in Science is remarkable for what it reveals about how OEA exerts its effects.
Scientists at Baylor College of Medicine led by Meng Wang, with some help from biochemists Eric Ortlund and Eric Armstrong at Emory, discovered that OEA is a way one part of the cell, the lysosome, talks to another part, the nucleus. Lysosomes are sort of recycling centers/trash digestersÂ (important for autophagy) and the nucleus is the control tower for the cell. The authors show that starting in lysosomes, OEA travels to the nucleus and activates nuclear hormone receptors (the Ortlund labâ€™s specialty). Continue reading “Unexpected mechanism for a longevity lipid”
Methylation, an epigenetic modification of DNA, can be thought of as a highlighter’s pen. Scientists have discovered that the pen comes in several colors.
Methylation, an epigenetic modification to DNA, can be thought of as a highlighting pen applied to DNAâ€™s text, adding information but not changing the actual letters of the text.
Are you still with me on the metaphors? If so, consider this wrinkle. (If not, more explanation here.)
Emory geneticist Peng Jin and his colleagues have been a key part of the discovery in the last few years that methylation comes in several colors. His lab has been mapping where 5-hydroxymethylcytosine or 5hmC appears in the genome and inferring how it functions. 5-hmC is particularly abundant in the brain.
Methylation, in the form of 5-methylcytosine or 5mC, is both a control button for turning genes off and a sign of their off state. 5hmC looks like 5mC, except it has an extra oxygen. That could be a tag for a removal, or a signal that aÂ gene is poised to be turned on.
Two recent papers on this topic:
Please recall that an enriched environment (exercise and mental stimulation) is good for learning and memory, for young and old. In the journalÂ Genomics, Jin and his team show that exposing mice to an enriched environmentÂ — a running wheel and a variety of toys — leads to a 60 percent reduction in 5hmC in the hippocampus, a region of the brain critical for learning and memory. Â The changes in 5hmC were concentratedÂ in genes having to do with axon guidance. Hat tip to the all-things-epigenetic site Epigenie.
In Genes and Development, structural biologist Xiaodong Cheng and colleagues demonstrateÂ that two regulatory proteins that bind DNA (Egr1 and WT1) respond primarily to oxidation of their target sequences rather than methylation. These proteins like plain old C and 5mC equally, but they donâ€™t like 5hmC or other oxidized forms of 5mC. â€œGene activity could plausibly be controlled on a much finer scale by these modifications than simply â€˜on or â€˜offâ€™,â€ the authors write.
Viral genes do frameshifting. Human genes do it too. Scientists want to use it to expand the genetic code. Emory scientists are figuring out the mechanism.
Itâ€™s a fundamental rule governing how the genetic code works. Ribosomes, the factories that assemble proteins in all types of living cells, read three letters (or nucleotides) of messenger RNA at a time.
In some instances, the ribosome can bend its rules, and read either two or four nucleotides, altering how downstream information is read. Biologists call this normallyÂ rare event ribosomal frameshifting. For an ordinary gene, the event of a frameshift turns the rest of the ensuing protein into nonsense. However,Â many virusesÂ exploit frameshifting, because they can then have overlapping genes and fit more information into a limitedÂ space.
Regulated frameshifting takes place in human genes too, and understanding frameshiftingÂ is key to recent efforts to expand the genetic code. Researchers are aiming to use the process to customize proteins for industrial and pharmaceutical applications, by inserting amino acid building blocks not found in nature.
â€œGoing back to the 1960s, when the genetic code was first revealed, there were many studies on ribosomal frameshifting, yet no-one really knows how it works on a molecular and mechanistic level,â€ says Christine Dunham, PhD, assistant professor of biochemistry at Emory University School of Medicine. â€œWhat we do know is that the â€˜yardstickâ€™ model that appears in a lot of textbooks, saying that the anticodon loop dictates the number of nucleotides decoded, while elegant, is probably incorrect.â€
Dunham, who first studied the topic as a postdoc, and her colleagues published a paper this week in PNAS where they outline a model for how ribosomal frameshifting occurs, based on structural studies of the ribosome interacting with some of its helper machinery. Co-first authors of the paper are postdoctoral fellows Tatsuya Maehigashi, PhD and Jack Dunkle, PhD.
ICYMI, part of an increasing interest in antibiotic resistance at Emory, coming from many angles: biochemistry/microbiology/infectious diseases.
Resistance to an entire class of antibiotics â€“ aminoglycosides — has the potential to spread to many types of bacteria, according to new biochemistry research.
A mobile gene called NpmA was discovered inÂ E. coliÂ bacteria isolated from a Japanese patient several years ago. Global spread of NpmA and related antibiotic resistance enzymes could disable an entire class of tools doctors use to fight serious or life-threatening infections.
Using X-ray crystallography, researchers at Emory made an atomic-scale snapshot of how the enzyme encoded by NpmA interacts with part of the ribosome, protein factories essential for all cells to function. NpmA imparts a tiny chemical change that makes the ribosome, and the bacteria, resistant to the drugsâ€™ effects.
The results, published in PNAS, provide clues to the threat NpmA poses, but also reveal potential targets to develop drugs that could overcome resistance from this group of enzymes.
Bacteria can survive antibiotic treatment through the process of persistence. Christine Dunham’s lab has been delving into odd couple proteins that regulate persistence.
When doctors treat disease-causing bacteria with antibiotics, a few bacteria can survive even if they do not have a resistance gene that defends them from the antibiotic. These rare, slow-growing or hibernating cells are called â€œpersisters.â€
Microbiologists see understanding persistence as a key to fighting antibiotic resistance and possibly finding new antibiotics. Persistence appears to be regulated by constantly antagonistic pairs of proteins called toxin-antitoxins.
Basically, the toxinâ€™s job is to slow down bacterial growth by interfering with protein production, and the antitoxinâ€™s job is to restrain the toxin until stress triggers a retreat by the antitoxin. Some toxins chew up protein-encoding RNA messages docked at ribosomes, but there are a variety of mechanisms. The genomes of disease-causing bacteria are chock full of these battling odd couples, yet not much was known about how they work in the context of persistence.
Biochemist Christine Dunham reports that several laboratories recently published papers directly implicating toxin-antitoxin complexes in both persistence and biofilm formation. Her laboratory has been delving into how the parts of various toxin-antitoxin complexes interact.
BCDB graduate student Marc Schureck and colleagues have determined the structure of a complex of HigBA toxin-antitoxin proteins from Proteus vulgaris bacteria via X-ray crystallography. The results were recently published in Journal of Biological Chemistry.
While Proteus vulgaris is known for causing urinary tract and wound infections, the HigBA toxin-antitoxin pair is also found in several other disease-causing bacteria such as V. cholera, P. aeruginosa, M. tuberculosis, S. pneumoniae etc.
â€œWe have been directly comparing toxin-antitoxin systems in E. coli, Proteus and M. tuberculosis to see if there are commonalities and differences,â€ Dunham says.
The P. vulgaris HigBA structure is distinctive because the antitoxin HigA does not wrap around and mask the active site of HigB, which has been seen in other toxin-antitoxin systems. Still, HigA clings onto HigB in a way that prevents it from jamming itself into the ribosome.
Biochemist Christine Dunham and her colleagues illuminate a long-standing puzzle concerning ribosomes, the factories inside cells that produce proteins.
Biochemist Christine Dunham and her colleagues have a new paper in PNAS illuminating a long-standing puzzle concerning ribosomes, the factories inside cells that produce proteins.
Ribosomes are where the genetic code â€œhappens,â€ because they are the workshops where messenger RNA is read out and proteins are assembled piece by piece. As a postdoc, Dunham contributed to Nobel Prize-winning work determining the molecular structure of the ribosome with mentor Venki Ramakrishnan.
The puzzle is this: how messenger RNA can be faithfully and precisely translated, when the interactions that hold RNA base pairs (A-U and G-C) together are not strong enough. There is enough â€œwobbleâ€ in RNA base pairing such that transfer RNAs that donâ€™t match all three letters on the messenger RNA can still fit.
To make progress in structural biology, look millions of years into the past. Emory biochemist Eric Ortlund and his colleagues have been taking the approach of â€œresurrectingâ€ ancient proteins to get around difficulties in probing their structures.
Ortlundâ€™s laboratory recently published a paper in Journal of Biological Chemistry describing the structure of a protein that is supposed to have existed 450 million years ago, in a complex with an anti-inflammatory drug widely used today. MSP graduate student Jeffrey Kohn is the first author.
Mometasone furoate is the active ingredient of drugs used to treat asthma, allergies and skin irritation. It is part of a class of drugs known as glucocorticoids, which can have a host of side effects such as reduced bone density and elevated blood sugar or blood pressure with long-term use.
One reason for these side effects is because the steroid receptor proteins that allow cells to detect and respond to hormones such as estrogen, testosterone, aldosterone and cortisol are all related. Mometasone is a good example of how glucocorticoids cross-react, Ortlund says. That made it an ideal test of the technique of mixing ancient receptors with modern drugs.
â€œWe used this structure to determine why mometasone cross reacts with the progesterone receptor, which regulates fertility, and why it inhibits the mineralocorticoid receptor, which regulates blood pressure,â€ he says.
Scientists have examined the sequences of the genes that encode these proteins at several points on the evolutionary tree, and used the information to reconstruct what the ancestral receptor looked like. This helps solve some problems that biochemists studying these proteins have had to deal with. One of these is: changing one amino acid in the protein sometimes means that the whole protein malfunctions.
â€œThe ancestral receptors are more tolerant to mutation, and they are more promiscuous with respect to activation,â€ Ortlund says. â€œThat is, they tend to respond to a wider array of endogenous steroid hormones, which makes sense in an evolutionary context. This enhanced activation profile and tolerance to mutation is what we feel makes them ideally suited to structure-function studies.â€
Biochemist Paul Doetschâ€™s recent appearance in a Science magazine feature on laboratory leadership led to a conversation with him about the challenges of graduate school.
He emphasized that scientific research is a team sport, and brilliance on the part of the lab head may not yield fruit without a productive relationship with the people in the lab. Doetsch suggested talking with Lydia Morris, a graduate student in the Genetics and Molecular Biology graduate program. Morris has been working in Doetsch’s lab for several years and is about to complete her degree. She has been examining the in vivo distribution of DNA repair proteins.
In this video, Morris and Doetsch talk about the differences between turn-the-crank and blue-sky projects, and the importance of backup projects, communications, high expectations and perseverance.