Biology subjects

Nelson, S. J.

Publications and source records attributed to Nelson, S. J..

4 recordsLinked to original sources

bioRxiv2020

Exploring the selenium-over-sulfur substrate specificity and kinetics of a bacterial selenocysteine lyase

Selenium is a vital micronutrient in many organisms. While traces are required for utilization by the microbe, excess amounts are toxic; thus, selenium can be regarded as a biological "double-edged sword". Selenium is chemically similar to the essential element sulfur, but curiously, evolution has selected the former over the latter for a subset of oxidoreductases. Enzymes involved in sulfur metabolism are less discriminate in terms of preventing selenium incorporation; however, its specific incorporation into selenoproteins reveals a highly discriminate process that is not completely understood. We have identified SclA, a selenocysteine lyase in the nosocomial pathogen, Enterococcus faecalis, and characterized its enzymatic activity and specificity for L-selenocysteine over L-cysteine. It is known that a single residue in the human selenocysteine lyase, D146, is considered to control selenocysteine specificity. Thus, using computational biology, we identified H100, a D146 ortholog in SclA, and generated mutant enzymes with site-directed mutagenesis. The proteins were overexpressed, purified, and characterized for their biochemical properties. All mutants exhibited varying levels of activity towards L-selenocysteine, suggesting a catalytic role for H100. Additionally, L-cysteine acted as a competitive inhibitor towards all enzymes with higher affinity than L-selenocysteine. Our findings offer key insight into the molecular mechanisms behind selenium-over-sulfur specificity and may further elucidate the role of selenocysteine lyases in vivo.

biochemistry↗

bioRxiv2019

Evaluation of IL-1 blockade as a host-directed therapy for tuberculosis in mice and macaques

In 2017 over 550,000 estimated new cases of multi-drug/rifampicin resistant tuberculosis (MDR/RR-TB) occurred, emphasizing a need for new treatment strategies. Linezolid (LZD) is a potent antibiotic for drug-resistant Gram-positive infections and is an effective treatment for TB. However, extended LZD use can lead to LZD-associated host toxicities, most commonly bone marrow suppression. LZD toxicities may be mediated by IL-1, an inflammatory pathway important for early immunity during M. tuberculosis infection. However, IL-1 can contribute to pathology and disease severity late in TB progression. Since IL-1 may contribute to LZD toxicity and does influence TB pathology, we targeted this pathway with a potential host-directed therapy (HDT). We hypothesized LZD efficacy could be enhanced by modulation of IL-1 pathway to reduce bone marrow toxicity and TB associated-inflammation. We used two animal models of TB to test our hypothesis, a TB-susceptible mouse model and clinically relevant cynomolgus macaques. Antagonizing IL-1 in mice with established infection reduced lung neutrophil numbers and partially restored the erythroid progenitor populations that are depleted by LZD. In macaques, we found no conclusive evidence of bone marrow suppression associated with LZD, indicating our treatment time may have been short enough to avoid the toxicities observed in humans. Though treatment was only 4 weeks (the FDA approved regimen at the time of study), we observed sterilization of the majority of granulomas regardless of co-administration of the FDA-approved IL-1 receptor antagonist (IL-1Rn), also known as Anakinra. However total lung inflammation was significantly reduced in macaques treated with IL-1Rn and LZD compared to LZD alone. Importantly, IL-1Rn administration did not impair the host response against Mtb or LZD efficacy in either animal model. Together, our data support that inhibition of IL-1 in combination with LZD has potential to be an effective HDT for TB and the need for further research in this area.

microbiology↗

bioRxiv2019

Tumor cell phenotype and heterogeneity differences in IDH1 mutant vs wild-type gliomas

Glioma is recognized to be a highly heterogeneous CNS malignancy, whose diverse cellular composition and cellular interactions have not been well characterized. To gain new clinical- and biological-insights into the genetically-bifurcated IDH1 mutant (mt) vs wildtype (wt) forms of glioma, we integrated multiplexed immunofluorescence single cell data for 43 protein markers across cancer hallmarks, in addition to cell spatial metrics, genomic sequencing and magnetic resonance imaging (MRI) quantitative features. Molecular and spatial heterogeneity scores for angiogenesis and cell invasion differ between IDHmt and wt gliomas irrespective of prior treatment and tumor grade; these differences also persisted in the MR imaging features of peritumoral edema and contrast enhancement volumes. Longer overall survival for IDH1mt glioma patients may reflect generalized altered cellular, molecular, spatial heterogeneity which manifest in discernable radiological manifestations.

genomics↗

bioRxiv2018

ORBIT: a new paradigm for geneticengineering of mycobacterial chromosomes

Current methods for genome engineering in mycobacteria rely on relatively inefficient recombination systems that require the laborious construction of a long double-stranded DNA substrate for each desired modification. We combined two efficient recombination systems to produce a versatile method for high-throughput chromosomal engineering that obviates the need for the preparation of double-stranded DNA recombination substrates. A synthetic \"targeting oligonucleotide\" is incorporated into the chromosome via homologous recombination mediated by the phage Che9c RecT annelase. This oligo contains a site-specific recombination site for the directional Bxb1 integrase (Int), which allows the simultaneous integration of a \"payload plasmid\" that contains a cognate recombination site and selectable marker. The targeting oligo and payload plasmid are co-transformed into a RecT- and Int-expressing strain, and drug-resistant homologous recombinants are selected in a single step. A library of reusable target-independent payload plasmids is available to generate knockouts and promoter replacements, or to fuse the C-terminal-encoding regions of target genes with tags of various functionalities. This new system is called ORBIT (Oligo-mediated Recombineering followed by Bxb1 Integrase Targeting) and is ideally suited for the creation of libraries consisting of large numbers of deletions, insertions or fusions in a target bacterium. We demonstrate the utility of ORBIT by the construction of insertions or deletions in over 100 genes in M. tuberculosis and M. smegmatis. The report describes the first genetic engineering technique for making selectable chromosomal fusions and deletions that does not require the construction of target- or modification-specific double-stranded DNA recombination substrates.

genetics↗