Article of the Month
Archive of previous entries
The primary component of most fungal cell walls is chitin, a natural polymer also found in the shells of crustaceans and insects. The human immune system recognizes chitin and can therefore repel most fungal pathogens. Some fungi produce enzymes known as chitin deacetylases that convert their cell wall chitin into a modified form known as chitosan, but incomplete conversion leads to the production of chitosan structures with multiple acetyl groups that still alert the immune system. In February's article of the month, Hembach et al. show how the aggressive fungal pathogen Cryptococcus neoformans has solved this problem by producing a deacetylase known as Cda4 that prefers chitosan as a substrate, thereby removing even more of the acetyl groups and forming a version of chitosan that is no longer perceived as a danger signal. The identification of this key enzyme provides a target for the development of new drugs to prevent cryptococcosis.
Article details: Hembach L et al. (2020) Unique subsite specificity and potential natural function of a chitosan deacetylase from the human pathogen Cryptococcus neoformans. Proc Natl Acad Sci USA 117 (7) 3551–3559.
Image shows encapsulated cells of the yeast Cryptococcus neoformans.
Image credit: CDC/Dr Leanor Haley.
Natural enzymes are usually optimized for industrial applications by introducing mutations that improve properties such as stability, substrate selection or catalytic turnover. Enzyme libraries can be combined with activity assays to screen large numbers of variants, and this is sufficient to screen all possible individual mutations at all sites. However, combinations of two or more mutations increase the number of potential variants far beyond current screening capabilities, and some kind of rational selection must be implemented to identify promising candidates. In January's article of the month, Ostafe et al. use machine learning to find the optimal combination of five independent mutations in the enzyme glucose oxidase, leading to an enzyme variant that remains active across a broad pH range and shows greater specificity for two different mediators. Machine learning can therefore be used to predict structure–activity relationships and streamline the optimization of enzymes by directed evolution.
Article details: Ostafe R et al. (2020) One‐shot optimization of multiple enzyme parameters: Tailoring glucose oxidase for pH and electron mediators. Biotechnol Bioeng 117 (1) 17–29.
Image shows a space-filling model of the enzyme glucose oxidase.
Image credit: wwPDB, created with NGL Viewer.
Plants flower in response to various environmental cues including the day length, a phenomenon known as photoperiodism. Some plants flower only when days are short, others only when days are long, and others like tobacco (Nicotiana tabacum) can flower regardless of the day length (day neutral). This is controlled by FLOWERING LOCUS T (FT) proteins, some acting as activators and some as repressors. In December's article of the month, Schmidt et al. analyze the role of the NtFT5 gene and report that it is an indispensable major floral activator during long days. They show that tobacco plants with only one functional copy of this gene remain in the vegetative growth phase for longer, producing about 10% more biomass before flowering and also producing more seeds. NtFT5 could therefore be used as a means to increase the yields of other crop species.
Article details: Schmidt FJ et al. (2020) The major floral promoter NtFT5 in tobacco (Nicotiana tabacum) is a promising target for crop improvement. Front Plant Sci 10, 1666.
Image shows flowering tobacco plants.
Image credit: H Zell (CC BY-SA 3.0).
Helicobacter pylori is a common bacterial pathogen in humans, causing chronic gastritis, ulcers and even stomach cancer. It is difficult to eradicate, and treatment usually involves multiple antibiotics, which can encourage the spread of antibiotic-resistant strains. In November's article of the month, Menchicchi et al. show that colloidal nanoparticles with an oily emulsion core and a coating of low-molecular-weight dextran sulfate can inhibit the adhesion of H. pylori to stomach cells, without signs of toxicity against gastrointestinal cell lines. These nanoparticles could therefore be developed as a complementary therapy against H. pylori, helping to reduce antibiotic use and prevent the emergence of multidrug-resistant bacteria.
Article details: Menchicchi B et al. (2019) Low-molecular-weight dextran sulfate nanocapsules inhibit the adhesion of Helicobacter pylori to gastric cells. ACS Appl Bio Mater 2 (11) 4777–4789.
Image shows the bacterium Helicobacter pylori.
Image credit: AJC1 (CC BY-SA 2.0).
Plant viruses are harmless to humans but have many favorable properties allowing them to be developed as imaging reagents, drug carriers and vaccines. In October's article of the month, Wang et al. show that the immunostimulatory properties of Cowpea mosaic virus in a mouse model of ovarian cancer differ according to whether they are presented as complete virus particles (including genomic RNA) or as empty protein shells. The two different forms trigger overlapping immune responses, with both types of particles promoting the secretion of cytokines and the stimulation of immune cells, but only the RNA-containing particles recruiting tumor-infiltrating neutrophils and other antigen-presenting cells to the tumor site. The detailed investigation of immune responses to different plant virus formulations will allow the development of tailored vaccines and adjuvants for cancer therapy.
Article details: Wang C et al. (2019) Cowpea mosaic virus nanoparticles and empty virus-like particles show distinct but overlapping immunostimulatory properties. J Virol 93 (21) e00129-19.
Image shows a computer model of Cowpea mosaic virus.
Image credit: wwPDB, created with NGL Viewer.
Alzheimer’s disease is a neurodegenerative disorder responsible for 60–70% of cases of dementia. There is growing evidence that vascular inflammation and leukocyte trafficking in the brain contribute to the disease, although the underlying mechanisms are unclear. In September's article of the month, Pietronigro et al. demonstrate that integrin α4β1 (also known as VLA-4) controls leukocyte–endothelial interactions in the brains of mice with Alzheimer-like pathology. VLA-4 was more abundant on certain T-cell populations and neutrophils in these mice, favoring their interaction with blood cells expressing the counterligand VCAM-1. Antibodies that block α4 integrins improved the memory of these mice and reduced the disease hallmarks, such as the accumulation of amyloid beta plaques and abnormal tau protein. The development of drugs that target α4 integrins could therefore improve the outlook for human Alzheimer’s patients.
Article details: Pietronigro E et al. (2019) Blockade of α4 integrins reduces leukocyte-endothelial interactions in cerebral vessels and improves memory in a mouse model of Alzheimer's disease. Sci Rep 9 (1) 12055.
Image shows an adherent T cell (stained pale blue for marker CD3) inside an endothelial vessel (stained yellow for marker VCAM-1) in the cortex of a mouse model of Alzheimer’s disease, with the nuclei of surrounding cells stained deep blue. Scale bar = 5 μm.
Image credit: Dr Gabriela Constantin, University of Verona/Scientific Reports (CC BY 4.0)
Plants are useful expression systems for recombinant proteins. However, screening many different expression constructs and/or conditions is time consuming and expensive because large numbers of plants must be grown and tested. It would be easier to screen plant cells, but results are not easily translatable from cells in culture to whole plants due to the dissimilar growth environments. In August's article of the month, Rademacher et al. describe an innovative screening platform in which plant cells grown in culture are compacted into porous aggregates called plant cell packs. These can be prepared at different scales, allowing screening in microtiter plates and direct scale-up to 150-mL columns. The results achieved in plant cell packs are similar to transient expression in whole plants. This new platform will allow the rapid screening of expression constructs and the production of recombinant proteins and metabolites at a variety of scales.
Article details: Rademacher T et al. (2019) Plant cell packs: a scalable platform for recombinant protein production and metabolic engineering. Plant Biotechnol J 17 (8) 1560–1566.
Image shows a microtiter plate containing plant cell packs expressing the fluorescent protein DsRed.
Image credit: Dr Thomas Rademacher, Fraunhofer IME/Plant Biotechnology Journal (CC BY 4.0).
The maize gene ZmBCH2 encodes the enzyme β-carotene hydroxylase 2, which converts β-carotene to zeaxanthin in the endosperm of maize seeds. In July's article of the month, Jin et al. show how the ZmBCH2 gene is regulated by testing a deletion series of the ZmBCH2 promoter linked to a reporter gene in transgenic maize, revealing that the 5' untranslated region is necessary for strong expression. By testing the reporter gene in rice, they were able to isolate the promoter from the effects of endogenous maize transcription factors. They were then able to express the reporter gene along with the maize transcription factors ZmPBF and ZmGAMYB in rice to show that the transcription factors have independent additive effects on gene expression. This provides a strategy for the quantitative control of gene expression in transgenic plants.
Article details: Jin X et al. (2019) ZmPBF and ZmGAMYB transcription factors independently transactivate the promoter of the maize (Zea mays) β-carotene hydroxylase 2 gene. New Phytol 222, 793–804.