The crystal structure of Pneumolysin at 2.0 Å resolution reveals the molecular packing of the pre-pore complex

Pneumolysin is a cholesterol-dependent cytolysin (CDC) and virulence factor of Streptococcus pneumoniae. It kills cells by forming pores assembled from oligomeric rings in cholesterol-containing membranes. Cryo-EM has revealed the structures of the membrane-surface bound pre-pore and inserted-pore oligomers, however the molecular contacts that mediate these oligomers are unknown because high-resolution information is not available. Here we have determined the crystal structure of full-length pneumolysin at 1.98 Å resolution. In the structure, crystal contacts demonstrate the likely interactions that enable polymerisation on the cell membrane and the molecular packing of the pre-pore complex. The hemolytic activity is abrogated in mutants that disrupt these intermolecular contacts, highlighting their importance during pore formation. An additional crystal structure of the membrane-binding domain alone suggests that changes in the conformation of a tryptophan rich-loop at the base of the toxin promote monomer-monomer interactions upon membrane binding by creating new contacts. Notably, residues at the interface are conserved in other members of the CDC family, suggesting a common mechanism for pore and pre-pore assembly

Elementary During a Pandemic

https://fisherpub.sjfc.edu/covid-journal-prose/1022/thumbnail.jp

An investigation of imaging approaches for the study of erbb2 distribution and dynamics in the plasma membrane with respect to the distribution of the tetraspanin cd82

Tetraspanin proteins are known to organise in the plasma membrane and form tetraspanin enriched microdomains. The tetraspanin CD82/KAI 1 has been shown previously by ensemble imaging and biochemical methods to associate with ErbB2, and it has been suggested that CD82 may play a role in regulating the distribution and dynamics ofErbB2 in the plasma membrane [1), [2]. CD82 may also play a role in mediating cellular response to Herceptin. In order to investigate the effect of CD82 on ErbB2 distribution and dynamics in the plasma membrane we applied a number of imaging techniques, in particular super resolution and single molecule approaches. We found little effect of CD82 expression on either ErbB2 diffusion or confinement characteristics in MCF7 and SKBR3 cells, and little difference in either the intrinsic clustering of ErbB2 or clustering in response to treatment with a panel of ErbB targeting molecules. We did however demonstrate and quantify the-importance of optimising both the imaging and analysis conditions for dual colour super-resolution imaging, and demonstrated for the first time the combination of super resolution optical fluctuation imaging and single molecule tracking

The association between overweight/obesity and double diabetes in adults with type 1 diabetes; a cross-sectional study

BACKGROUND: Double Diabetes (DD), type 1 diabetes (T1DM) + insulin resistance (IR), is associated with increased risk of micro/macro-vascular complications and mortality. Obesity can contribute to the development of DD. This study explored the prevalence of overweight/obesity and their association with DD in adults with T1DM. METHODS: Cross-sectional study of consecutive adults with T1DM attending diabetes clinics in a secondary care hospital (January-November 2019). Estimated glucose disposal rate (eGDR) was used as a marker of IR, and an eGDR < 8 was used to identify individuals with DD. RESULTS: One hundred seven adults with T1DM were included; female/male: 51/56; age [median (inter-quartile range): 30.0 (23-51) years]; BMI 25.4 (22.8-30.0) kg/m 2. Overweight/obesity prevalence was 57/107 (53.3 %) [overweight: 30/107 (28 %); obesity: 27/107 (25.2 %)]. Compared to those with normal BMI, individuals with T1DM and overweight/obesity had longer diabetes duration; higher total daily insulin dose; and higher DD prevalence: 48/57 (84.2 %) vs. 14/50 (28 %) (p < 0.01); with similar HbA1c. BMI correlated with total daily insulin dose (rho = 0.55; p < 0.01). Individuals with DD were older, had longer duration of diabetes, higher HbA1c, and more adverse lipid profile and microalbuminuria compared to those without DD. CONCLUSIONS: Overweight/obesity is very common in adults with T1DM, and is associated with double diabetes. BMI is positively associated with total insulin dose. Double diabetes is associated with adverse cardiovascular risk profile and is also common in lean individuals with T1DM. Further research is needed to examine the impact of overweight/obesity in people with T1DM and whether weight loss in this population can improve diabetes-related outcomes

A novel strategy for the identification of genomic islands by comparative analysis of the contents and contexts of tRNA sites in closely related bacteria

We devised software tools to systematically investigate the contents and contexts of bacterial tRNA and tmRNA genes, which are known insertion hotspots for genomic islands (GIs). The strategy, based on MAUVE-facilitated multigenome comparisons, was used to examine 87 Escherichia coli MG1655 tRNA and tmRNA genes and their orthologues in E.coli EDL933, E.coli CFT073 and Shigella flexneri Sf301. Our approach identified 49 GIs occupying ∼1.7 Mb that mapped to 18 tRNA genes, missing 2 but identifying a further 30 GIs as compared with Islander [Y. Mantri and K. P. Williams (2004), Nucleic Acids Res., 32, D55–D58]. All these GIs had many strain-specific CDS, anomalous GC contents and/or significant dinucleotide biases, consistent with foreign origins. Our analysis demonstrated marked conservation of sequences flanking both empty tRNA sites and tRNA-associated GIs across all four genomes. Remarkably, there were only 2 upstream and 5 downstream deletions adjacent to the 328 loci investigated. In silico PCR analysis based on conserved flanking regions was also used to interrogate hotspots in another eight completely or partially sequenced E.coli and Shigella genomes. The tools developed are ideal for the analysis of other bacterial species and will lead to in silico and experimental discovery of new genomic islands