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
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.
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
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
Ribosomes, the factories that assemble proteins in cells, read three letters of messenger RNA at a time. Occasionally, the ribosome can bend its rules, and read either two or four nucleotides, altering how downstream information is read: frameshifting.
This week, Christine Dunham’s lab in the Department of Biochemistry has a paper in PNAS on how ribosomal frameshifting works, one of several she has published on this topic. The first author is postdoc Samuel Hong, now at MD Anderson. A commentary in PNAS calls their paper a “major advance” and “culmination of a half-century quest.”
A suppressor tRNA can occupy more than one site on the ribosome. Adapted figure courtesy of Christine Dunham
Some antibiotics disrupt protein synthesis by encouraging frameshifting to occur, so a thorough understanding of frameshifting benefits antibiotic research. Also, scientists are aiming to use the process to customize proteins for industrial and pharmaceutical applications, by inserting amino acid building blocks not found in nature.
When mutations add or subtract a letter from a protein-coding gene, that usually turns the rest of the gene to nonsense. Compensatory mutations in the same gene can push the genetic letters back into the correct frame. However, others are separate, found within the machinery for translating the genetic code, namely transfer RNAs: the adaptors that bring amino acids into the ribosome. Suppressor tRNAs can compensate for a forward frameshift in another gene.
The Dunham lab’s new paper solves the structure of a bacterial ribosome undergoing “recoding” influenced by a suppressor tRNA. Her group had previously captured how the ribosomes decode this tRNA in one site of the ribosome, the aminoacyl or A site, in a 2014 PNAS paper. The new structures show how the tRNA moves through the ribosome out-of-frame to recode. The tRNA undergoes unusual rearrangements that cause the ribosome to lose its grip on the mRNA frame and allows the tRNA to form new interactions with the ribosome to shift into a new reading frame.
Congratulations to Christine Dunham and colleagues in the Department of Biochemistry for their first cryo-electron microscopy paper, recently published in the journal Structure.
The paper solves the structure of a bacterial ribosome bound to a messenger RNA containing a loop that regulates translation. This process is important for the study of several neurological diseases such as fragile X syndrome, for example.
Christine Dunham, PhD
Dunham writes: “We are focusing on establishing this in bacteria to understand frameshifting and protein folding as a consequence of codon preference. We will then build up our knowledge to potentially study eukaryotic translational control.”
The paper neatly links up with two Nobel Prizes: the 2017 Chemistry prize for cryo-electron microscopy and the 2009 Chemistry prize for ribosome structure, awarded in part to Dunham’s mentor Venki Ramakrishnan. Also, see this 2015 feature from Nature’s Ewen Callaway outlining how cryo-EM is a must have for structural biologists wanting to probe large molecules that are difficult to crystallize.
Construction now underway in the Biochemistry Connector will allow installation of microscopes (worth $6 million) necessary for Dunham and others to do cryo-EM here at Emory, although she advises that it will be several months until they are photo-op ready. For the Structure paper, Dunham collaborated with George Skiniotis at University of Michigan; he recently moved to Stanford. Read more
Imagine a shaker table, where kids can assemble a structure out of LEGO bricks and then subject it to a simulated earthquake. The objective is to design the most stable structure.
Biochemists face a similar task when they are attempting to design thermostable proteins, with heat analogous to shaking. Thermostable proteins, which do not become unfolded/denatured at high temperatures, are valuable for industrial processes.
Now imagine that these stable structures have to also perform a function. This is the two-part challenge of designing thermostable proteins. They have to maintain their physical structure, and continue to perform their function adequately, all at high temperatures.
Eric Ortlund and colleagues, working with Eric Gaucher at Georgia Tech*, have a new paper published in Structure, in which they examine different ways to achieve this goal in a component of the protein synthesis machinery, EF-Tu. This protein exists in both mesophilic bacteria, which live at around human body temperature, and thermophilic organisms (think: hot springs).
A previous analysis by Gaucher used the ASR technique (ancestral sequence reconstruction) to resurrect ancient, extinct EF-Tus and characterize them. It was shown that that ancestral EF-Tus were thermostable and functional. EF-Tu’s thermostability declined along with the environmental temperature; ancestral bacteria started off living in hot environments and those environments cooled off over millions of years.
In the new paper, Ortlund and first author Denise Okafor show that stable proteins generated by protein engineering methods do not always retain their functional capabilities. However, the ASR technique has a unique advantage, Ortlund says. By accounting for the evolutionary history of the protein, it preserves the natural motions required for normal protein function. Their results suggest that ASR could be used to engineer thermostability in other proteins besides EF-Tu.
*Gaucher recently moved to Georgia State.
Kishore Kumar Jella, PhD
Winship Cancer Institute postdoc Kishore Kumar Jella has been invited to speak at the NATO advanced research workshop “BRITE (Biomarkers of Radiation In the Environment): Robust tools for Risk Assessment” in Yerevan, Armenia, on 28-30 November, 2017. The workshop brings together leading international experts to evaluate currently and developing radiation biomarkers for environmental applications.
Jella works in the Departments of Biochemistry and Radiation Oncology under the direction of Professors William S. Dynan and Mohammad K. Khan. He will speak on “Exosomes as Radiation Biomarkers”. He will describe how radiation influences exosome production and how these exosomes influence the immune system. The work has applications both to radiation carcinogenesis and combination radio-immunotherapy.
Jella is supported in part by a grant from the National Aeronautics and Space Administration to Dynan.
Exosomes are nano-sized membrane-clothed capsules containing proteins and RNA that are thought to facilitate cell-cell communcation. They were previously implicated in the ability of cancer cells to influence healthy neighbor cells, and have also been proposed as anti-cancer therapeutic vehicles. Jella’s previous research on exosomes and radiation-induced bystander signaling was published in Radiation Research in 2014.