Artificial retina using synthetic and biological materials

A synthetic, soft tissue retina made of hydrogels and biological cell membrane proteins was developed by an Oxford University student Vanessa Restrepo-Schild. Research involved combining biological and synthetic tissues in a laboratory. Designed like a camera, the aqueous droplets containing bacteriorhodopsin (bR), a light-driven proton pump act as pixels, detecting and reacting to light to generate electrical signals, which can stimulate the neurons with resulting output recognized in grey scale.

The retina replica consists of soft water droplets (hydrogels) and biological cell membrane proteins.
Credit: Oxford University

The study, published in the journal Scientific Reports, shows that unlike existing artificial retinal implants, the cell-cultures are created from natural, biodegradable materials and do not contain foreign bodies or living entities. In this way the implant is less invasive than a mechanical devise, and is less likely to have an adverse reaction on the body.

This research could revolutionize the bionic implant industry with development of new, less invasive technologies that more closely resemble human body tissues, helping to treat degenerative eye conditions such as retinitis pigmentosa.

Currently synthetic retina has only been tested in laboratory conditions and further research is needed to see viability of this technology.

Miss Restrepo-Schild has filed a patent for the technology and the next phase of the work will see the Oxford team expand the replica’s function to include recognising different colours. Working with a much larger replica, the team will test the material’s ability to recognise different colours and potentially even shapes and symbols. Looking further ahead the research will expand to include animal testing and then a series of clinical trials in humans.

Citation: Schild, Vanessa Restrepo, Michael J. Booth, Stuart J. Box, Sam N. Olof, Kozhinjampara R. Mahendran, and Hagan Bayley. “Light-Patterned Current Generation in a Droplet Bilayer Array.” Scientific Reports 7 (2017): 46585. doi:10.1038/srep46585.
Adapted from press release by the Oxford University.

Researchers create heat stable vaccines using silica

Researchers at the University of Bath, working with colleagues at the University of Newcastle, have created a technique which can keep vaccines intact at high temperatures by encasing them in silica cages. When a protein in solution is mixed with silica, silicon dioxide binds closely around the protein to match its shape and encases the protein. A major advantage of this method is that it doesn’t require freeze-drying, something that around half of all vaccines won’t survive intact. A powder of ensilicated proteins and the silica cage enveloping the protein means it can be heated to 100°C or stored at 22°C for at least six months with no loss of function.

Once the protein has been encased in silica it can be stored or transported without refrigeration before the silica coat can be removed chemically, leaving the proteins unaffected.

The discovery means that vaccines and other important medicines could be transported much more easily, cheaply and safely, especially to remote areas or places lacking infrastructure where the need is often greatest.

The teams call their method ensilication and hope it will solve the costly and often impractical need for a cold chain to protect protein-based products including vaccines, antibodies and enzymes. The research is published in the journal Scientific Reports. The research team tested the method on three proteins; one from a tetanus vaccine, horse haemoglobin and an enzyme from egg white.

Citation: Chen, Yun-Chu, Tristan Smith, Robert H. Hicks, Aswin Doekhie, Francoise Koumanov, Stephen A. Wells, Karen J. Edler, Jean Van Den Elsen, Geoffrey D. Holman, Kevin J. Marchbank, and Asel Sartbaeva. “Thermal stability, storage and release of proteins with tailored fit in silica.” Scientific Reports 7 (2017): 46568.
Research funding: Royal Society, The Annett Trust
Adapted from press release by the University of Bath.

Microgravity and cellular adaptation

Based on real-time readings on the ISS conducted by ESA astronaut Samantha Cristoforetti, University of Zurich scientists Oliver Ullrich and Cora Thiel can now reveal that cells are able to respond to changes in gravitational conditions very quickly and continue functioning. The research team used the alleged oxidative burst an old evolutionary mechanism to exterminate bacteria via defense cells to understand how rat cells responded to changes in gravity.

Picture of experiment equipment. Credit: C. Thiel und Airbus DS

With the help of centrifuges, Cristoforetti altered the gravitational conditions on the ISS, that enabled the research team on earth to track how the cells reacted.

“Although the immune defense collapsed as soon as zero gravity hit, to our surprise the defense cells made a full recovery within 42 seconds.” For Ullrich and Thiel, the direct evidence of a rapid and complete adaptation to zero gravity in less than a minute begs the question as to whether previous cell changes measured after hours or days were also the result of an adaptation process.

“It seems paradoxical,” says Thiel: “Cells are able to adapt ultra-rapidly to zero gravity. However, they were never exposed to it in the evolution of life on Earth. Therefore, the results raise more questions regarding the robustness of life and its astonishing adaptability.” In any case, as far as Ullrich is concerned the result of the ISS experiment is good news for manned space flight: “There’s hope that our cells are able to cope much better with zero gravity than we previously thought.”

Citation: Thiel, Cora S., Diane De Zélicourt, Svantje Tauber, Astrid Adrian, Markus Franz, Dana M. Simmet, Kathrin Schoppmann, Swantje Hauschild, Sonja Krammer, Miriam Christen, Gesine Bradacs, Katrin Paulsen, Susanne A. Wolf, Markus Braun, Jason Hatton, Vartan Kurtcuoglu, Stefanie Franke, Samuel Tanner, Samantha Cristoforetti, Beate Sick, Bertold Hock, and Oliver Ullrich. “Rapid adaptation to microgravity in mammalian macrophage cells.” Scientific Reports 7, no. 1 (2017). doi:10.1038/s41598-017-00119-6.
Adapted from press release by the University of Zurich.

I-Wire, a new Heart-on-a-Chip device to study biomechanical properties of heart

Scientists at Vanderbilt University have created a 3D organ-on-a-chip that can mimic the biomechanical properties of the heart. The device and the results of initial experiments are reported in the journal Acta Biomaterialia (for links see below).

View of the cardiac fiber in the I-Wire device at two levels of magnification.
Credit: VIIBRE Vanderbilt University

The unique aspect of the new device, which represents about two-millionths of a human heart, is that it controls the mechanical force applied to cardiac cells.  This allows the researchers to reproduce the mechanical conditions of the living heart in addition to its electrical and biochemical environment.

“We created the I-Wire Heart-on-a-Chip so that we can understand why cardiac cells behave the way they do by asking the cells questions, instead of just watching them,” said Gordon A. Cain University Professor John Wikswo, who heads up the project. “We believe it could prove invaluable in studying cardiac diseases, drug screening and drug development, and, in the future, in personalized medicine by identifying the cells taken from patients that can be used to patch damaged hearts effectively.”

The I-Wire device consists of a thin thread of human cardiac cells 0.014 inches thick (about the size of 20-pound monofilament fishing line) stretched between two perpendicular wire anchors. The amount of tension on the fiber can be varied by moving the anchors in and out, and the tension is measured with a flexible probe that pushes against the side of the fiber. The fiber is supported by wires and a frame in an optically clear well that is filled with a liquid medium like that which surrounds cardiac cells in the body. The apparatus is mounted on the stage of a powerful optical microscope that records the fiber’s physical changes. The microscope also acts as a spectroscope that can provide information about the chemical changes taking place in the fiber. A floating microelectrode also measures the cells’ electrical activity.

According to the researchers, the I-Wire system can be used to characterize how cardiac cells respond to electrical stimulation and mechanical loads and can be implemented at low cost, small size and low fluid volumes, which make it suitable for screening drugs and toxins. Because of its potential applications, Vanderbilt University has patented the device. Unlike other heart-on-a-chip designs, I-Wire allows the researchers to grow cardiac cells under controlled, time-varying tension similar to what they experience in living hearts.

To demonstrate the I-Wire’s value in determining the effects that different drugs have on the heart, the scientists tested its response with two drugs known to affect heart function in humans: isoproterenol and blebbistatin. Isoproterenol is a medication used to treat bradycardia (slow heart rate) and heart block (obstruction of the heart’s natural pacemaker). Blebbistatin inhibits contractions in all types of muscle tissue, including the heart.

According to Veniamin Sidorov, the research assistant professor at the Vanderbilt Institute for Integrative Biosystems Research and Education (VIIBRE) who led its development, the device faithfully reproduces the response of cardiac cells in a living heart.

1. Sidorov, Veniamin Y., Philip C. Samson, Tatiana N. Sidorova, Jeffrey M. Davidson, Chee C. Lim, and John P. Wikswo. “I-Wire Heart-on-a-Chip I: Three-dimensional cardiac tissue constructs for physiology and pharmacology.” Acta Biomaterialia 48 (2017): 68-78. doi:10.1016/j.actbio.2016.11.009.
2. Schroer, Alison K., Matthew S. Shotwell, Veniamin Y. Sidorov, John P. Wikswo, and W. David Merryman. “I-Wire Heart-on-a-Chip II: Biomechanical analysis of contractile, three-dimensional cardiomyocyte tissue constructs.” Acta Biomaterialia 48 (2017): 79-87. doi:10.1016/j.actbio.2016.11.010.

Research funding: National Institutes of Health, National Science Foundation, Defense Threat Reduction Agency, American Heart Association, Department of Veterans Affairs.
Adapted from press release by Vanderbilt University. 

Obesity genes: role of foraging gene in fruit fly

A University of Toronto study on fruit flies has uncovered a gene that could play a key role in obesity in humans. The paper published online this month in Genetics examines a “foraging gene” humans share in common with the flies, which plays multiple roles and is found in similar places, such as the nervous system, in the muscle and in fat.

“What our study does is nails the gene for being very important for the traits of moving, feeding and fat storage,” says University Professor Marla Sokolowski of the Department of Ecology & Evolutionary Biology in U of T’s Faculty of Arts & Science.

In nature, fruit flies called “Rovers” with high amounts of the gene tend to move a lot, eat very little and stay lean, while flies with low amounts of for called “Sitters” are the opposite. The same could apply to obesity in humans.

“So you could imagine if you are a fly, preferences for sugar, the tendency to store a lot of fat and the tendency to move less could all be contributing to the likelihood of being more obese if you have low levels of this gene, or to be leaner if you have higher levels.”

Such similarities between species are known as orthologs, meaning they are genes that evolved from a common ancestor eons ago.

The study involved a technique called recombineering to manipulate DNA at the molecular level, so as to remove and then reinsert the gene in various doses to see the effects on behavior and metabolism.

“To be able to take a gene of this large size and complexity and put it back in the fly so that it works is almost at the edge of what is possible,” Sokolowski says it’s particularly interesting that one gene should have multiple roles in feeding and obesity in the body, a characteristic known as pleiotropy.

The next question would be how exactly it plays multiple roles. “Lots of genes have multiple roles, but the idea here is that this gene may be involved in the coordination of roles in traits important for feeding and obesity.”

 “We don’t know much about pleiotropy, or how it happens, or how it’s regulated at the level of the molecules. So this sets the groundwork to be able to look at that in detail.”

Citation: Allen, Aaron M., Ina Anreiter, Megan C. Neville, and Marla B. Sokolowski. “Feeding-Related Traits Are Affected by Dosage of the foraging Gene in Drosophila melanogaster.” Genetics 205, no. 2 (2016): 761-73.
Research funding: Natural Sciences and Engineering Council of Canada, Canadian Institutes for Health Research.
Adapted from press release by the University of Toronto.

Analysis of interactome of Zika virus infected neural cells shows altered expression of more than 500 proteins

Zika virus (ZIKV) interferes with the cellular machinery controlling cell division and alters the expression of hundreds of genes responsible for guiding the formation and development of brain cells, according to findings of research published in Scientific Reports.

Zika virus wikipedia
Zika virus structure. Credit: Wikipedia / David Goodwill

The association between Zika virus (ZIKV) infection and microcephaly has been previously established. Nevertheless, the cellular changes caused by the virus and leading to microcephaly are largely unknown. “Elucidating the foundations of Zika virus infection is crucial in order to develop tools against it”, says Stevens Rehen, the principal investigator of the study and a researcher working at the D’ Or Institute for Research and Education (IDOR) and at the Institute of Biomedical Sciences at Federal University of Rio de Janeiro (UFRJ) in Brazil.

In a previous study published by the group in Science magazine, researchers observed that the pool of human neural stem cells infected by the Brazilian strain of Zika virus was rapidly and completely depleted if compared to non-infected cells. This finding led the group to further investigate how Zika virus disrupts the interactome map (or molecular fingerprinting) of infected cells – which is the entire set of cellular and molecular interactions in a given cell group. The analysis of the interactome of Zika-infected cells may reveal the cellular targets and pathways with which the virus interacts or which it modulates, offering valuable opportunities for drug design.

To this end, human neural cells were infected by a strain of Zika virus (ZIKV) obtained from a Brazilian patient. These cells were then made into neurospheres, which are organized 3D aggregates of neural cells resembling fetal brain tissue that recapitulate many of the normal early and crucial processes that the brain undergoes through development and thus are a great model for studying the human brain. Next, the group identified the molecular fingerprinting of infected and non-infected cells by checking the expression level and status of innumerous genes and proteins.

The analysis revealed that more than 500 proteins in infected neurospheres had their expression level or status (upregulated vs downregulated) altered, if compared to non-infected neurospheres. A number of these altered proteins are normally involved with tasks such as fixing DNA damage or assuring chromosomal stability. Also, proteins that are normally required for cell growth were silent in infected neurospheres, which may explain why Zika-infected cells die much sooner than their non-infected counterparts. Interestingly, genes driving cell specialization were also silent in infected neurospheres, precluding that specialized brain cells were generated. On the other hand, proteins associated with viral replication were over-abundant, most likely the result of a strategy adopted by the virus to promote its own replication in the host cell. A complete list of all human proteins that have been found altered in Zika-infected neurospheres is available in the study entitled “Zika virus disrupts molecular fingerprinting of human neurospheres”, published in Scientific Reports this week. 

According to Patricia Garcez, Assistant Professor at the Federal University of Rio de Janeiro and the first author of the study: “these findings provide insights into the molecular mechanisms of Zika virus (ZIKV) infection over the course of brain development and may explain some of the consequences seen in the brain of newborns with microcephaly”.

Citation: Patricia P. Garcez, Juliana Minardi Nascimento, Janaina Mota de Vasconcelos, Rodrigo Madeiro da Costa, Rodrigo Delvecchio, Pablo Trindade, Erick Correia Loiola, Luiza M. Higa, Juliana S. Cassoli, Gabriela Vitória, Patricia C. Sequeira, Jaroslaw Sochacki, Renato S. Aguiar, Hellen Thais Fuzii, Ana M. Bispo de Filippis, João Lídio da Silva Gonçalves Vianez Júnior, Amilcar Tanuri, Daniel Martins-de-Souza & Stevens K. Rehen. “Zika virus disrupts molecular fingerprinting of human neurospheres.” Scientific Reports 7, Article number: 40780 (2017).
DOI: 10.1038/srep40780
Research funding: Brazilian Development Bank, Funding Authority for Studies and Projects, National Council of Scientific and Technological Development, Foundation for Research Support – State of Rio de Janeiro, São Paulo Research Foundation.
Adapted from press release by D’ Or Institute for Research and Education (IDOR).

Research in mice shows molecular mechanism underlying Oxycodone addiction

RGS9-2, a key signaling protein in the brain known to play a critical role in the development of addiction-related behaviors, acts as a positive modulator of oxycodone reward in both pain-free and chronic pain states, according to a study conducted at the Icahn School of Medicine at Mount Sinai and published in the journal Neuropsychopharmacology. The mechanisms of oxycodone action uncovered through this study will help scientists and physicians develop strategies and tools to dissociate the analgesic (pain relief) actions of opioids from the addiction-related effects.

Pixabay images

Using mouse models of acute and chronic pain, Mount Sinai researchers found that RGS9-2, the intracellular protein that controls the function of opioid receptors in the brain reward center, promotes addiction to oxycodone in pain-free, acute, and chronic pain states. Mice that lacked the gene responsible for encoding RGS9-2 (RGS9KO mice) showed less propensity to develop addiction-related behaviors. Furthermore, the loss of RGS9-2 function does not affect the acute analgesic effects of oxycodone. The research team also found that RSG9-2 plays a protective role towards the development of oxycodone tolerance, as RGS9KO mice became tolerant to the analgesic effects of the drug earlier than those that had the gene. Researchers found that the same mechanisms control sensitivity to oxycodone addiction in pain-free as well as chronic pain states.

Oxycodone is a painkiller that is widely prescribed for acute and chronic pain conditions and is also among the most abused opioids. Oxycodone acts on the same brain receptors as morphine and heroin, the mu opioid receptors, which are present in many areas of the brain that mediate pain relief but are also expressed in the brain network associated with addiction. While there has been an extensive investigation into the mechanisms underlying the analgesia, dependence, and addiction potential of morphine, the mechanism by which oxycodone exerts its actions remained unknown.

“Although oxycodone produces similar analgesic and behavioral effects to those observed with morphine, our study demonstrates that the intracellular actions of morphine and oxycodone are distinct,” says Venetia Zachariou, Ph.D., Associate Professor in the Fishberg Department of Neuroscience and The Friedman Brain Institute, Icahn School of Medicine at Mount Sinai. “Our work reveals that intracellular factors that prevent the actions of morphine may actually promote the actions of oxycodone. This information is particularly important for pain management strategies, as a common course is to have patients oscillate between oxycodone and morphine to achieve pain relief.”

This study provides new information on pathways involved in behavioral responses to oxycodone in pain-free and neuropathic pain states, which will help researchers and clinicians to determine the risks and benefits of oxycodone prescription for the treatment of pain. This knowledge may lead to the development of more efficacious and less addictive compounds for pain management.

Citation: Sevasti Gaspari, Valeria Cogliani, Lefteris Manouras, Ethan M Anderson, Vasiliki Mitsi, Kleopatra Avrampou, Fiona B Carr and Venetia Zachariou. “RGS9-2 Modulates Responses to Oxycodone in Pain-Free and Chronic Pain States.” Neuropsychopharmacology 2017.
DOI: 10.1038/npp.2017.4
Research funding: National Institute of Neurological Disorders and Stroke
Adapted from press release by The Mount Sinai Hospital.

Researchers develop in vitro model of brain for research

Harvard University researchers have developed a multiregional brain-on-a-chip that models the connectivity between three distinct regions of the brain. The in vitro model was used to extensively characterize the differences between neurons from different regions of the brain and to mimic the system’s connectivity.  The research was published in the Journal of Neurophysiology.

Image of the in vitro model showing three distinct regions of the brain connected by axons.
Credit: Disease Biophysics Group/Harvard University

“The brain is so much more than individual neurons,” said Ben Maoz, co-first author of the paper and postdoctoral fellow in the Disease Biophysics Group in the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS). “It’s about the different types of cells and the connectivity between different regions of the brain. When modeling the brain, you need to be able to recapitulate that connectivity because there are many different diseases that attack those connections.”

Researchers from the Disease Biophysics Group at SEAS and the Wyss Institute modeled three regions of the brain most affected by schizophrenia the amygdala, hippocampus and prefrontal cortex. They began by characterizing the cell composition, protein expression, metabolism, and electrical activity of neurons from each region in vitro.

“It’s no surprise that neurons in distinct regions of the brain are different but it is surprising just how different they are,” said Stephanie Dauth, co-first author of the paper and former postdoctoral fellow in the Disease Biophysics Group. “We found that the cell-type ratio, the metabolism, the protein expression and the electrical activity all differ between regions in vitro. This shows that it does make a difference which brain region’s neurons you’re working with.”

Next, the team looked at how these neurons change when they’re communicating with one another. To do that, they cultured cells from each region independently and then let the cells establish connections via guided pathways embedded in the chip.

The researchers then measured cell composition and electrical activity again and found that the cells dramatically changed when they were in contact with neurons from different regions.

“When the cells are communicating with other regions, the cellular composition of the culture changes, the electrophysiology changes, all these inherent properties of the neurons change,” said Maoz. “This shows how important it is to implement different brain regions into in vitro models, especially when studying how neurological diseases impact connected regions of the brain.”

To demonstrate the chip’s efficacy in modeling disease, the team doped different regions of the brain with the drug Phencyclidine hydrochloride commonly known as PCP which simulates schizophrenia. The brain-on-a-chip allowed the researchers for the first time to look at both the drug’s impact on the individual regions as well as its downstream effect on the interconnected regions in vitro.

The brain-on-a-chip could be useful for studying any number of neurological and psychiatric diseases, including drug addiction, post-traumatic stress disorder, and traumatic brain injury.

“To date, the Connectome project has not recognized all of the networks in the brain,” said Parker. “In our studies, we are showing that the extracellular matrix network is an important part of distinguishing different brain regions and that, subsequently, physiological and pathophysiological processes in these brain regions are unique. This advance will not only enable the development of therapeutics, but fundamental insights as to how we think, feel, and survive.”

Citation: Dauth, Stephanie, Ben M. Maoz, Sean P. Sheehy, Matthew A. Hemphill, Tara Murty, Mary Kate Macedonia, Angie M. Greer, Bogdan Budnik, and Kevin Kit Parker. “Neurons derived from different brain regions are inherently different in vitro: A novel multiregional brain-on-a-chip.” Journal of Neurophysiology (2016): jn-00575.
DOI: 10.1152/jn.00575.2016
Research funding: Defense Advanced Research Projects Agency.
Adapted from press release by Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS).

Using ribosomal protein expression patterns as cancer biomarker

A research team at the University of Basel’s Biozentrum has investigated the expression of ribosomal proteins in a wide range of human tissues including tumors and discovered a cancer type specific signature. The study is reported in journal Genome Biology. Researchers think that these signature could be used for predicting progression and survival.

Gene expression level of individual ribosomal proteins (RP) in different types of cancer (blue: lower level; red: higher level compared to normal tissue). Credit: Mihaela Zavolan and Joao Guimaraes, University of Basel, Biozentrum

Prof. Mihaela Zavolan’s research group at the Biozentrum of the University of Basel has now discovered that about a quarter of the ribosomal proteins have tissue-specific expression and that different cancer types have their own individual expression pattern of ribosomal proteins. In the future, these patterns may serve as a prognostic marker for cancer and may point towards new therapeutic opportunities.

Mihaela Zavolan and her co-worker Joao Guimaraes have systematically analyzed ribosomal protein expression in thirty tissue types, three hundred different cell types and sixteen different types of tumors, such as lung and breast cancer. In contrast to previous assumptions, they found a wide variability in ribosomal protein gene expression. In particular, hematopoietic and tumor cells display the most complex expression pattern.

“For us, it was really impressive to see that consistent signatures emerged for the different cancer types after the analysis of distinct data sets including patient samples,” explains first author Guimaraes. “The pattern of the dysregulated proteins is very striking, whereby the expression of some ribosomal proteins is systematically reduced, and of others increased in cancer cells. This suggests that individual ribosomal proteins can either suppress or promote tumorogenesis.”

Furthermore, the scientists discovered a strong relationship between the “signature” in breast cancer and the relapse-free survival. “We were quite surprised to find that the expression level of just three ribosomal proteins allows a fairly accurate prognosis of disease progression, comparable to the best predictive markers that are currently known”, Zavolan points out.

“Our study demonstrates the potential of such expression signatures for the prognosis and perhaps a diagnosis of cancer. We are especially interested in studying the functions of individual ribosomal proteins and hopefully opening the door for new therapeutic options,” explains the scientist.
Citation: Guimaraes, Joao C., and Mihaela Zavolan. “Patterns of ribosomal protein expression specify normal and malignant human cells.” Genome Biology 2016 17:236.
DOI: 10.1186/s13059-016-1104-z
Adapted from press release by University of Basel.

Research unveils structure of crucial bacterial cell wall protein

Duke University researchers have provided the first close-up glimpse of a protein, called MurJ, which is crucial for building the bacterial cell wall and protecting it from outside attack. The research is published in Nature Structural and Molecular Biology.

Researchers at Duke University solved the structure of an enzyme that is crucial for helping bacteria build their cell walls. The molecule, called MurJ (shown in green), must flip cell wall precursors (purple) across the bacteria’s cell membrane before these molecules can be linked together to form the cell wall. This new structure could be important to help develop new broad-spectrum antibiotics. Credit: Alvin Kuk, Duke University

“Until now, MurJ’s mechanisms have been somewhat of a ‘black box’ in the bacterial cell wall synthesis because of technical difficulties studying the protein,” said senior author Seok-Yong Lee, Ph.D., associate professor of biochemistry at Duke University School of Medicine. “Our study could provide insight into the development of broad spectrum antibiotics, because nearly every type of bacteria needs this protein’s action.”

A bacterium’s cell wall is composed of a rigid mesh-like material called peptidoglycan. Molecules to make peptidoglycan are manufactured inside the cell and then need to be transported across the cell membrane to build the outer wall.

In 2014, another group of scientists had discovered that MurJ is the transporter protein located in the cell membrane that is responsible for flipping these wall building blocks across the membrane. Without MurJ, peptidoglycan precursors build up inside the cell and the bacterium falls apart. Many groups have attempted to solve MurJ’s structure without success, partly because membrane proteins are notoriously difficult to work with.

In this study, Lee’s team was able to crystallize MurJ and determine its molecular structure to 2-angstrom resolution by an established method called X-ray crystallography, which is difficult to achieve in a membrane protein. The structure, combined with follow-up experiments in which the scientists mutated specific residues of MurJ, allowed them to propose a model for how it flips peptidoglycan precursors across the membrane.

After determining the first structure of MurJ, Lee’s team is now working to capture MurJ in action, possibly by crystallizing the protein while it is bound to a peptidoglycan precursor. “Getting the structure of MurJ linked to its substrate will be key. It will really help us understand how this transporter works and how to develop an inhibitor targeting this transporter,” Lee said.

Lee’s group is continuing structure and function studies of other key players in bacterial cell wall biosynthesis as well. Last year, they published the structure of another important enzyme, MraY, bound to the antibacterial muraymycin.

Citation: Kuk, Alvin CY, Ellene H. Mashalidis, and Seok-Yong Lee. “Crystal structure of the MOP flippase MurJ in an inward-facing conformation.” Nature Structural & Molecular Biology (2016).
DOI: 10.1038/nsmb.3346
Research funding: Duke University
Adapted from press release by the Duke University.