Linkage between fitness of yeast cells and adenylate kinase catalysis

Enzymes have evolved with highly specific values of their catalytic parameters kcat and KM. This poses fundamental biological questions about the selection pressures responsible for evolutionary tuning of these parameters. Here we are address these questions for the enzyme adenylate kinase (Adk) in eukaryotic yeast cells. A plasmid shuffling system was developed to allow quantification of relative fitness (calculated from growth rates) of yeast in response to perturbations of Adk activity introduced through mutations. Biophysical characterization verified that all variants studied were properly folded and that the mutations did not cause any substantial differences to thermal stability. We found that cytosolic Adk is essential for yeast viability in our strain background and that viability could not be restored with a catalytically dead, although properly folded Adk variant. There exist a massive overcapacity of Adk catalytic activity and only 12% of the wild type kcat is required for optimal growth at the stress condition 20°C. In summary, the approach developed here has provided new insights into the evolutionary tuning of kcat for Adk in a eukaryotic organism. The developed methodology may also become useful for uncovering new aspects of active site dynamics and also in enzyme design since a large library of enzyme variants can be screened rapidly by identifying viable colonies

The virulence and infectivity of Listeria monocytogenes are not substantially altered by elevated SigB activity

Listeria monocytogenes is a bacterial pathogen capable of causing severe infections but also thriving outside the host. To respond to different stress conditions, L. monocytogenes mainly utilizes the general stress response regulon, which largely is controlled by the alternative sigma factor Sigma B (SigB). In addition, SigB is important for virulence gene expression and infectivity. Upon encountering stress, a large multicomponent protein complex known as the stressosome becomes activated, ultimately leading to SigB activation. RsbX is a protein needed to reset a "stressed"stressosome and prevent unnecessary SigB activation in nonstressed conditions. Consequently, absence of RsbX leads to constitutive activation of SigB even without prevailing stress stimulus. To further examine the involvement of SigB in the virulence of this pathogen, we investigated whether a strain with constitutively active SigB would be affected in virulence factor expression and/or infectivity in cultured cells and in a chicken embryo infection model. Our results suggest that increased SigB activity does not substantially alter virulence gene expression compared with the wild-type (WT) strain at transcript and protein levels. Bacteria lacking RsbX were taken up by phagocytic and nonphagocytic cells at a similar frequency to WT bacteria, both in stressed and nonstressed conditions. Finally, the absence of RsbX only marginally affected the ability of bacteria to infect chicken embryos. Our results suggest only a minor role of RsbX in controlling virulence factor expression and infectivity under these conditions

A Highly Substituted Ring-Fused 2-Pyridone Compound Targeting PrfA and the Efflux Regulator BrtA in Listeria monocytogenes

ABSTRACT Listeria monocytogenes is a facultative Gram-positive bacterium that causes listeriosis, a severe foodborne disease. We previously discovered that ring-fused 2-pyridone compounds can decrease virulence factor expression in Listeria by binding and inactivating the PrfA virulence activator. In this study, we tested PS900, a highly substituted 2-pyridone that was recently discovered to be bactericidal to other Gram-positive pathogenic bacteria, such as Staphylococcus aureus and Enterococcus faecalis. We show that PS900 can interact with PrfA and reduce the expression of virulence factors. Unlike previous ring-fused 2-pyridones shown to inactivate PrfA, PS900 had an additional antibacterial activity and was found to potentiate sensitivity toward cholic acid. Two PS900-tolerant mutants able to grow in the presence of PS900 carried mutations in the brtA gene, encoding the BrtA repressor. In wild-type (WT) bacteria, cholic acid binds and inactivates BrtA, thereby alleviating the expression of the multidrug transporter MdrT. Interestingly, we found that PS900 also binds to BrtA and that this interaction causes BrtA to dissociate from its binding site in front of the mdrT gene. In addition, we observed that PS900 potentiated the effect of different osmolytes. We suggest that the increased potency of cholic acid and osmolytes to kill bacteria in the presence of PS900 is due to the ability of the latter to inhibit general efflux, through a yet-unknown mechanism. Our data indicate that thiazolino 2-pyridones constitute an attractive scaffold when designing new types of antibacterial agents. IMPORTANCE Bacteria resistant to one or several antibiotics are a very large problem, threatening not only treatment of infections but also surgery and cancer treatments. Thus, new types of antibacterial drugs are desperately needed. In this work, we show that a new generation of substituted ring-fused 2-pyridones not only inhibit Listeria monocytogenes virulence gene expression, presumably by inactivating the PrfA virulence regulator, but also potentiate the bactericidal effects of cholic acid and different osmolytes. We identified a multidrug repressor as a second target of 2-pyridones. The repressor–2-pyridone interaction displaces the repressor from DNA, thus increasing the expression of a multidrug transporter. In addition, our data suggest that the new class of ring-fused 2-pyridones are efficient efflux inhibitors, possibly explaining why the simultaneous addition of 2-pyridones together with cholic acid or osmolytes is detrimental for the bacterium. This work proves conclusively that 2-pyridones constitute a promising scaffold to build on for future antibacterial drug design

Favorable outcome with sentinel lymph node biopsy alone after neoadjuvant chemotherapy in clinically node positive breast cancer at diagnosis: Turkish Multicentric NEOSENTI-TURK MF-18-02-study.

Purpose: Factors affecting local outcome were evaluated in patients with clinically node-positive (cN+) breast cancer at diagnosis, who underwent sentinel lymph node biopsy (SLNB) alone after neoadjuvant chemotherapy (NAC). Methods: Between 2004 and 2018, 303 cytopathology-proven cN (+) patients in a multicentric registry, who received NAC and underwent SLNB alone were analysed. All patients had regional nodal irradiation. Results: Median age was 46 (23-70). Of those, 211 patients had ypN0 disease (69.6%), whereas 92 pa-tients had ypN (+) disease including 19 (20.6%) isolated tumor cells (ITC), 33 micrometastases (35.9%) and 40 macrometastases (43.5%). At a median follow-up of 36 months (24-172), one patient (0.3%) with macrometastatic SLN was found to have locoregional recurrence as chest wall and supraclavicular LN metastases at the 60th month. Five-year disease-free survival (DFS) and disease specific survival (DSS) rates were 87% and 95%, respectively. Patients with cT3/4 (HR = 2.41, 95% CI; 1.14-5.07), non-luminal molecular pathology (HR = 2.60, 95% CI, 1.16-5.82), and non-pCR in the breast (HR = 2.11, 95% CI, 0.89-5.01) were found to have an increased HR compared to others in 5-year DFS. However, no dif-ference could be found between ypN0 and ypN ITC and micrometastasis (HR = 1.23, 95% CI, 0.44-3.47), whereas there was a slight increase in HR of patients with ypN macrometastasis versus ypN0 (HR = 1.91, 95% CI, 0.63-5.79). Conclusion: ALND could be avoided in meticulously selected cN (+) patients who underwent SLNB after NAC having breast and/or nodal pCR, cT1-2, or low volume residual nodal disease with luminal pa-thology, as long as axillary radiotherapy is provided. (c) 2021 Published by Elsevier Ltd

Blastic Plasmacytoid Dendritic Cell Neoplasm: Skin and Bone Marrow Infiltration of Three Cases and the Review of the Literature

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a distinct and rare neoplastic entity and was classified as a subgroup of acute myeloblastic leukemia by the WHO in 2008. The median survival of patients was 15.2 months in a large case series. Allogeneic or autologous bone marrow transplantation has been recommended by some reports because of the disease's poor prognosis. We present three patients who presented with both skin and bone marrow infiltration. A 57-year-old man, a 62-year-old woman, a 64-year-old man were admitted to our outpatient clinic because of skin lesions. All of the patient's had bone marrow infiltration with positivity of the CD4, CD56, and CD123 staining. Survival of the patient's were 42, 6 and 12 months, respectively. Two of the patients who presented as blastic form didn't respond to any chemotherapy. BPDCN is a difficult disease to diagnosis and manage. CD4, CD56, CD123, CD303, and T cell leukemia/lymphoma 1. Cutaneous lesions can present as isolated nodules, macules, and disseminated macules and nodules. Positivities are crucial to the diagnosis of the disease in histological examination. Bone marrow infiltration or disease relapse at presentation were related to poor prognosis. Complete immunocytochemical staining must be performed for all patients who have cutaneous lesions with or without blood count abnormalities. Bone marrow (allogeneic or autologous) transplantation should be considered at the first remission