From the journals: November 2018

We offer a selection of recent papers on a variety of topics from the Journal of Biological Chemistry, the Journal of Lipid Research and Molecular & Cellular Proteomics.

The complex life cycle of bones

Lateral meningocele syndrome, also known as Lehman syndrome, is a rare genetic disorder affecting the musculoskeletal system. The disorder is associated with gain-of-function mutations in the gene for the transmembrane receptor Notch3. Ernesto Canalis and colleagues at UConn Health examined the effects of these mutations on the mouse skeleton to understand the role of Notch3 in bone formation. They found that the mutant Notch3 triggered increased osteoblast proliferation, which counterintuitively resulted in reduced bone volume because of increased bone resorption. The findings were published in the Journal of Biological Chemistry.

Structure determines bacterial virulence

Campylobacter concisus and Campylobacter jejuni are both gram-negative bacteria that occupy the same ecological niche. While C. jejuni has been studied extensively in the pathogenesis of gastrointestinal diseases, there is very little information regarding the pathogenicity of C. concisus in such disorders. In a recent study published in the Journal of Lipid Research, Katja Brunner and colleagues at University College London investigated the structural differences of lipooligosaccharide, a common virulence factor known as LOS, between the two bacterial species. Through extensive mass spectrometry studies, the authors showed that the backbone of LOS in C. concisus is less phosphorylated and lacks sialylation, which hampers the interaction of the bacteria with a transmembrane protein that causes adherence, invasion and production of pro-inflammatory mediators. This study provides insight to differences in the LOS structure of these two organisms and how that correlates with their virulence.

Arctic insights into rubisco

The CO2-fixing enzyme rubisco is the most abundant enzyme on earth, but its catalytic properties vary among species. Marine phytoplankton generally have some of the most efficient rubisco enzymes known. Among the phytoplankton, diatoms are major players in the marine carbon cycle, but their rubisco enzymes have not been characterized. Karin Valegård and colleagues at Uppsala University showed that rubisco enzymes from five arctic diatom species were heavily post-translationally modified, suggesting that the role of these modifications in rubisco function should be investigated further. The findings were published in the Journal of Biological Chemistry.

How a common drug causes liver failure

Acetaminophen is a common pain reliever found in every pharmacy. However, it is also the No. 1 cause of acute liver failure in the United States. In the liver, acetaminophen is converted into a new compound that covalently binds to proteins with thiol groups. These covalent binding events contribute to the toxicity of acetaminophen, but they do not account fully for its role in liver failure.

James Chun Yip Chan and colleagues at the National University of Singapore examined a post-translational modification known as glutathionylation to understand its role in acetaminophen toxicity. In a study published in the journal Molecular & Cellular Proteomics, they showed that acetaminophen induces protein glutathionylation, which leads to mitochondrial dysfunction, deficits in energy metabolism and other effects linked to acetaminophen toxicity. This research helps explain a potential marker of drug toxicity and may be used in the future to reduce cases of liver failure worldwide.

Understanding an anti-malarial target

Efforts to control malaria are thwarted by drug resistance, motivating the search for new anti-malarial drugs. Several anti-malarial clinical candidates act on the ATPase PfATP4 in malaria parasites. PfATP4 is difficult to express heterologously, so its function has been poorly understood, and efforts to design better molecules that target it have been limited. James E.O. Rosling and colleagues at Australian National University developed a membrane ATPase assay to examine PfATP4’s biochemical properties. In the Journal of Biological Chemistry, they reported that PfATP4 is a pH-sensitive sodium transporter and identified the range of its sensitivity to an anti-malarial molecule under physiologically relevant conditions.

Vitamin E formulations in low blood cholesterol

Chylomicron retention disease, known as CMRD, and abetalipoproteinemia, or ABL, are rare genetic disorders that cause impairment in absorption of fats and certain vitamins, resulting in hypocholesterolemia. One of the hallmarks of this group of diseases is severe vitamin E deficiency. Charlotte Cuerq and colleagues at Lyon Sud Hospital investigated the effect of two formulations of vitamin E (Tocofersolan and alpha-tocopherol acetate) on patients with CMRD and ABL in comparison to healthy volunteers.

In a paper published in the Journal of Lipid Research, they showed that in CMRD patients, Tocofersolan is better absorbed than the alternative formulation, as measured by a higher bioavailability after a single dose administration. To study how these two formulations change the absorption and storage of vitamin E, the authors administered the molecules for four months and found that vitamin E levels are higher in red blood cells, adipose tissue and plasma of patients with CMRD irrespective of the formulation. These observations are consistent with the less severe clinical phenotype in patients with CMRD than in patients with ABL.

Transcription factor allows parasite hijacking

Leishmania are intracellular parasites that deactivate host macrophages to evade the immune system. Previous evidence suggested that the parasite manipulated host miRNA as part of this process. In a paper in the Journal of Biological Chemistry, Lucie Colineau and colleagues at the University of British Columbia confirmed that Leishmania infection uniformly downregulated host cell miRNA expression. They also showed that this effect depended on expression of the host transcription factor c-Myc. Silencing c-Myc restored miRNA expression and reduced Leishmania’s intracellular survival.

Identifying bias in gene expression profiles

The compact nucleus of a cell houses all the information needed to make thousands of proteins. This information is found within genes that are organized carefully into clusters. Clustered genes often are transcribed into mRNA at the same time even though they may not be functionally related. However, research in cell lines has shown that cells can regulate expression of these unrelated genes at the protein level.

Piotr Grabowski and colleagues at the Institute of Biotechnology in Berlin examined factors that may contribute to the coexpression of functionally unrelated genes. In a study published in the journal Molecular & Cellular Proteomics, they describe how they used mouse tissues to show that epigenetics play an important role in regulating the coexpression of certain genes, but coexpression was buffered at the protein level. This research suggests that monitoring protein coexpression may be more useful than studying mRNA coexpression data for understanding functional genomics.

A key enzyme in pseudoephedrine synthesis

Ephedrine and pseudoephedrine are pharmacologically important molecules produced by plants. The biosynthetic pathways in plants that produce these molecules are incompletely characterized, and commercial production of these molecules uses chemical rather than biological synthesis. In a study published in the Journal of Biological Chemistry, Jeremy S. Morris and colleagues at the University of Calgary identified the N-methyltransferase responsible for the final step in the synthesis of these molecules in Ephedra sinica. They then showed that this enzyme, when heterologously expressed in E. coli, was able to produce (pseudo)ephedrine, potentially paving the way for commercial production by engineered micro-organisms.

New opportunities to treat cholera

Cholera infection causes deadly dehydrating diarrhea, but the molecular details of how it does so are incompletely known. Diarrhea occurs when the chloride transporter cystic fibrosis transmembrane conductance regulator, or CFTR, is activated by cyclic adenosine monophosphate, or cAMP, in intestinal cells, but which biochemical pathway cAMP comes from in this context was unclear. Andrew Thomas and colleagues at Cincinnati Children’s Hospital Medical Center showed that the cAMP-generating adenylate cyclase AC6 is associated with CFTR in epithelial cells. When challenged with cholera toxin, cells in which AC6 was knocked out did not secrete fluid, suggesting that the AC6-CFTR complex could be a target for anti-diarrheal drugs. The findings were published in the Journal of Biological Chemistry.