Promiscuous protein droplets regulate immune gene activity

Biochemists at Emory are achieving insights into how an important regulator of the immune system switches its function, based on its orientation and local environment. New research demonstrates that the glucocorticoid receptor (or GR) forms droplets or “condensates” that change form, depending on its available partners.

The inside of a cell is like a crowded nightclub or party, with enzymes and other proteins searching out prospective partners. The GR is particularly well-connected and promiscuous, and has the potential to interact with many other proteins. It is a type of protein known as a transcription factor, which turns some genes on and others off, depending on how it is binding DNA.

These are fluorescent droplets of the glucocorticoid receptor (GR) in red, with a coregulator protein in green. When DNA is added, the co-regulator forms its own droplets on the surface of GR droplets. Image courtesy of Filipp Frank

“It is now thought that most transcription factors form or are recruited into condensates, and that condensation modulates their function,” says Filipp Frank, PhD, first author of the paper and a postdoctoral instructor in Eric Ortlund’s lab in the Department of Biochemistry. “What’s new is that we identified a DNA-dependent change in GR condensates, which has not been described for other transcription factors.”

The results are published in Proceedings of the National Academy of Sciences. Ortlund is a co-author of the paper, along with postdoctoral fellow Xu Liu, PhD.

Understanding how the GR works could help researchers find anti-inflammatory drugs with reduced side effects. The GR is the target for corticosteroid drugs such as dexamethasone, which is currently used to treat COVID-19 as well as allergies, asthma and autoimmune diseases.

Corticosteroids’ harmful side effects are thought to come from turning on genes involved in metabolism and bone growth, while their desired anti-inflammatory effects result from turning other inflammatory and immune system genes off. Researchers want to find alternatives that could separate those two functions.

Posted on July 21, 2021 by Quinn Eastman in Cancer, Immunology Leave a comment

New antibiotic tactic vs gonorrhea

A new antibiotic compound can clear infection of multi-drug resistant gonorrhea in mice with a single oral dose, according to a new study led by researchers at Penn State and Emory.

Like other antibiotics, this one targets the ribosome, the factories that generate proteins in bacterial (and human) cells. But it does so at a site that is different from other antibiotics. This one interferes with the process of trans-translation, which bacteria use to rescue their ribosomes out of rough spots.

The results were published in Nature Communications. This was a collaboration involving several groups: biochemist Christine Dunham’s at Emory and Ken Keiler’s at Penn State, along with others at Florida State, the Uniformed Services University and the Massachusetts-based pharmaceutical company Microbiotix.

Zachary Aron, director of chemistry at Microbiotix, is the first author of the paper, and the compound is called MBX-4132. It is also active against other Gram-positive bacteria, including tuberculosis and Staph aureus, and the company says it will continue to optimize it.

At Emory, Dunham’s lab used cryo-electron microscopy to produce high-resolution images of the compound as it binds to the bacterial ribosome — see below.

Christine Dunham’s lab specializes in ribosomal structural studies

“A derivative of MBX-4132 binds to a location on the ribosome that is different from all known antibiotic binding sites,” Dunham says. “The new drug also displaces a region of a ribosomal protein that we think could be important during the normal process of trans-translation. Because trans-translation only occurs in bacteria and not in humans, we hope that the likelihood of the compound affecting protein synthesis in humans is greatly reduced, a hypothesis strongly supported by the safety and selectivity studies performed by Microbiotix.”

Multi-drug resistant gonorrhea is listed by the CDC as one of the five most urgent threats, among antibiotic resistant bacteria. Half of all gonorrhea infections are resistant to at least one antibiotic.

Posted on March 25, 2021 by Quinn Eastman in Uncategorized Leave a comment

Don’t go slippery on me, tRNA

RNA can both carry genetic information and catalyze chemical reactions, but it’s too wobbly to accurately read the genetic code by itself. Enzymatic modifications of transfer RNAs – the adaptors that implement the genetic code by connecting messenger RNA to protein – are important to stiffen and constrain their interactions.

Biochemist Christine Dunham’s lab has a recent paper in eLife showing a modification on a proline tRNA prevents the tRNA and mRNA from slipping out of frame. The basics of these interactions were laid out in the 1980s, but the Dunham lab’s structures provide a comprehensive picture with mechanistic insights.

The mRNA code for proline is CCC – all the nucleotides are the same — so it is susceptible to frameshifting.

The paper includes videos that virtually unwrap the RNA interactions. The X-ray crystal structures indicate that tRNA methylation – a relatively small bump — at position 37 influences interactions between the tRNA and the ribosome.

Posted on November 12, 2020 by Quinn Eastman in Uncategorized Leave a comment

Tweaks to corticosteroids may reduce side effects

Steroid anti-inflammatory drugs such as dexamethasone and prednisone are widely used to treat conditions such as allergies, asthma, autoimmune diseases, cancer – and now, COVID-19. Yet they can have harmful side effects on the skin, bones and metabolism.

The side effects are thought to come from a molecular mechanism that is separate from the anti-inflammatory one, and scientists have envisioned that it may be possible to divide the two. A new paper in PNAS from Emory biochemist Eric Ortlund’s lab sketches out how one potential alternative may work.

Synthetic corticosteroids mimic the action of the stress hormone cortisol; both bind the glucocorticoid receptor (GR) protein. Ortlund’s group obtained structural information on how vamorolone, an experimental drug, sticks to the part of GR that binds hormones.

The American company ReveraGen and Swiss partner Santhera are developing vamorolone for Duchenne muscular dystrophy, but it is possible to envision several other conditions such as ulcerative colitis for which vamorolone or a similar drug could be helpful. Vamorolone is NOT approved by the FDA for Duchenne muscular dystrophy or any other indication.

As far as its interaction with GR, what sets vamorolone apart from conventional corticosteroids is quite subtle: a missing hydrogen bond. This means that GR doesn’t interact as well with various partner proteins, which are needed to turn on genes involved in processes such as metabolism and bone growth. However, the anti-inflammatory effects result mainly from turning inflammatory and immune system genes off, and those interactions are maintained. More on that distinction here and here.

Posted on September 11, 2020 by Quinn Eastman in Uncategorized Leave a comment

Burning fat like a baby

Newborn humans and hibernating mammals have high levels of brown adipose tissue, which they use to generate heat. Adult humans generally don’t have abundant brown adipose tissue, even if they have lots of “white” fat. Increasing brown fat’s activity may be an approach to treat obesity and related metabolic disorders.

Recently researchers identified an enzyme called Them1 (thioesterase superfamily member 1) as a factor that limits heat generation in brown adipose tissue. Emory biochemist Eric Ortlund and his lab showed how part of the Them1 enzyme binds a certain type of lipid molecule, and also how that part of the enzyme anchors the enzyme close to lipid droplets in adipose cells. Former graduate student Matt Tillman, now a postdoc at Duke, was the first author of the new paper in Proceedings of the National Academy of Sciences.

“In this study, we show Them1 contains a lipid sensor module that detects specific lipids within the cell to regulate its activity,” says Tillman.

In brown adipose cells, the lipid-sensing domain of Them1 is needed for localization around lipid droplets

From Tillman et al PNAS (2020)

He and his colleagues showed that a lipid known for its role in cell signaling, lysophosphatidylcholine or LPC, inhibits Them1 activity, which in turn activates thermogenesis in brown adipose tissue. In contrast, other fatty acids that serve as fuel tend to activate Them1. This regulatory system within Them1 allows the cell to sense its metabolic state and decide when to burn or conserve fat.

Posted on August 21, 2020 by Quinn Eastman in Uncategorized Leave a comment

Triple play in science communication

Emory BCDB graduate student Emma D’Agostino

We are highlighting Emory BCDB graduate student Emma D’Agostino, who is a rare triple play in the realm of science communication.

Emma has her own blog, where she talks about what it’s like to have cystic fibrosis. Recent posts have discussed the science of the disease and how she makes complicated treatment decisions together with her doctors. She’s an advisor to the Cystic Fibrosis Foundation on patient safety, communicating research and including the CF community in the research process. She’s also working in biochemist Eric Ortlund’s lab on nuclear receptors in the liver:drug targets for the treatment of diabetes and intestinal diseases.

The triple play is this — on her blog, Emma has discussed how she has to deal with antibiotic resistance. Emory Antibiotic Resistance Center director David Weiss’ lab has published a lot on colistin: how it’s a last-resort drug because of side effects, and how difficult-to-detect resistance to it is spreading. Emma has some personal experience with colistin that for me, brought the issue closer. Read more

Posted on July 20, 2020 by Quinn Eastman in Uncategorized Leave a comment

Super-cold technique = hot way to see enzyme structure

In the last decade, a revolution has been taking place in structural biology, the field in which scientists produce detailed maps of how enzymes and other machines in the cell work. That revolution is being driven by cryo-electron microscopy (cryo-EM for short), which is superseding X-ray crystallography as the main data-production technique and earned a chemistry Nobel in 2017.

Just before COVID-19 sent some Emory researchers home and drove others to pivot their work toward coronavirus, Lab Land had a chance to tour the cryo-EM facility and take photos, with the help of Puneet Juneja, director of the core. Juneja demonstrated how samples are prepared for data collection — see the series of photos below.

Someone coming into the facility in the Biochemistry Connector area will notice a sign telling visitors and those passing by to stay quiet (forgot to take a photo of that!). The facility has electrical shielding and temperature/humidity controls. Also two levels of cooling are required for samples, since they are flash-frozen or “vitrified” in liquid ethane, which is in turn cooled by liquid nitrogen. The cooling needs to happen quickly so that ice crystals do not form. The massive cryo-EM equipment rests on a vibration-reduction platform; no music and no loud conversation are allowed during data collection.

One of the first structures obtained in this relatively new facility was the structure of a viral RNA polymerase, the engine behind viral replication. It wasn’t a coronavirus enzyme – it was from RSV (respiratory syncytial virus).

Still, cryo-EM is a way to visualize exactly how drugs that inhibit the SARS-CoV-2 polymerase – such as remdesivir or Emory’s own EIDD-2801 – exert their effects. Chinese researchers recently published a cryo-EM structure of the SARS-CoV-2 polymerase with remdesivir in Science. Read more

Posted on April 13, 2020 by Quinn Eastman in Immunology, Uncategorized Leave a comment

Tracking how steroid hormone receptor proteins evolved

When thinking about the evolution of female and male, consider that the first steroid receptor proteins, which emerged about 550 million years ago, were responsive to estrogen. The ancestor of other steroid hormone receptors, responsive to hormones such as testosterone, progesterone and cortisol, emerged many millions of years later.

Blue = estrogen-responsive receptors, Orange = non-aromatized (progesterone, testosterone, cortisol) hormone-responsive

Biochemist Eric Ortlund and colleagues have a new paper in Structure that reconstructs how interactions of steroid receptor proteins evolved over time. This is a complex area to model, since the receptors change shape when they bind their respective hormones, allowing them to bring in other proteins and activate genes.

First author C. Denise Okafor, a FIRST postdoctoral fellow at Emory, will be starting a position as assistant professor at Penn State next month.

The scientists also show that a mutation in the mineralocorticoid receptor associated with severe hypertension (S810L), which makes the receptor more promiscuous, restores an ancestral interaction within the protein.

“Evolutionary substitutions rewired the networks, subsequently altering hormonal interactions and allowing steroid receptors to achieve ligand specificity over time,” the authors write.

Posted on December 9, 2019 by Quinn Eastman in Uncategorized Leave a comment

Biochemists grab slippery target: LRH-1

To fight fat, scientists had to figure out how to pin down a greasy, slippery target. Researchers at Emory University and Baylor College of Medicine have identified compounds that potently activate LRH-1, a liver protein that regulates the metabolism of fat and sugar. These compounds have potential for treating diabetes, fatty liver disease and inflammatory bowel disease.

Their findings were recently published online in Journal of Medicinal Chemistry.

LRH-1 is thought to sense metabolic state by binding a still-undetermined group of greasy molecules: lipids or phospholipids. It is a nuclear receptor, a type of protein that turns on genes in response to hormones or vitamins. The challenge scientists faced was in designing drugs that fit into the same slot occupied by the lipids.

“Phospholipids are typically big, greasy molecules that are hard to deliver as drugs, since they are quickly taken apart by the digestive system,” says Eric Ortlund, PhD, associate professor of biochemistry at Emory University School of Medicine. “We designed some substitutes that don’t fall apart, and they’re highly effective – 100 times more potent that what’s been found already.”

Previous attempts to design drugs that target LRH-1 ran into trouble because of the grease. Two very similar molecules might bind LRH-1 in opposite orientations. Ortlund’s lab worked with Emory chemist Nathan Jui, PhD and his colleagues to synthesize a large number of compounds, designing a “hook” that kept them in place. Based on previous structural studies, the hook could stop potential drugs from rotating around unpredictably. Read more

Posted on September 30, 2019 by Quinn Eastman in Uncategorized Leave a comment

Shape-shifting RNA regulates viral sensor

Congratulations to Emory biochemists Brenda Calderon and Graeme Conn. Their recent Journal of Biological Chemistry paper on a shape-shfting RNA was selected as an Editor’s Pick and cited as a “joy to read… Technically, the work is first class, and the writing is clear.”

Calderon, a former BCDB graduate student and now postdoc, was profiled by JBC in August.

Brenda Calderon, PhD

Calderon and Conn’s JBC paper examines regulation of the enzyme OAS (oligoadenylate synthetase). OAS senses double-stranded RNA: the form that viral genetic material often takes. When activated, OAS makes a messenger molecule that drives internal innate immunity enzymes to degrade the viral material (see below).

OAS is in turn regulated by a non-coding RNA, called nc886. Non-coding means this RNA molecule is not carrying instructions for building a protein. Calderon and Conn show that nc886 takes two different shapes and only one of them activates OAS.

Conn says in a press release prepared by JBC that although nc886 is present in all human cells, it’s unknown how abundance of its two forms might change in response to infection. Read more

Posted on October 29, 2018 by Quinn Eastman in Uncategorized Leave a comment

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