Role of the horizontal gene exchange in evolution of pathogenic Mycobacteria

Background

Mycobacterium tuberculosis is one of the most dangerous human pathogens, the causative agent of tuberculosis. While this pathogen is considered as extremely clonal and resistant to horizontal gene exchange, there are many facts supporting the hypothesis that on the early stages of evolution the development of pathogenicity of ancestral Mtb has started with a horizontal acquisition of virulence factors. Episodes of infections caused by non-tuberculosis Mycobacteria reported worldwide may suggest a potential for new pathogens to appear. If so, what is the role of horizontal gene transfer in this process?

Results

Availing of accessibility of complete genomes sequences of multiple pathogenic, conditionally pathogenic and saprophytic Mycobacteria, a genome comparative study was performed to investigate the distribution of genomic islands among bacteria and identify ontological links between these mobile elements. It was shown that the ancient genomic islands from M. tuberculosis still may be rooted to the pool of mobile genetic vectors distributed among Mycobacteria. A frequent exchange of genes was observed between M. marinum and several saprophytic and conditionally pathogenic species. Among them M. avium was the most promiscuous species acquiring genetic materials from diverse origins.

Conclusions

Recent activation of genetic vectors circulating among Mycobacteria potentially may lead to emergence of new pathogens from environmental and conditionally pathogenic Mycobacteria. The species which require monitoring are M. marinum and M. avium as they eagerly acquire genes from different sources and may become donors of virulence gene cassettes to other micro-organisms.

     

Nucleation of β-rich oligomers and β-barrels in the early aggregation of human islet amyloid polypeptide

The self-assembly of human islet amyloid polypeptide (hIAPP) into β-sheet rich amyloid aggregates is associated with pancreatic β-cell death in type 2 diabetes (T2D). Prior experimental studies of hIAPP aggregation reported the early accumulation of α-helical intermediates before the rapid conversion into β-sheet rich amyloid fibrils, as also corroborated by our experimental characterizations with transmission electron microscopy and Fourier transform infrared spectroscopy. Although increasing evidence suggests that small oligomers populating early hIAPP aggregation play crucial roles in cytotoxicity, structures of these oligomer intermediates and their conformational conversions remain unknown, hindering our understanding of T2D disease mechanism and therapeutic design targeting these early aggregation species. We further applied large-scale discrete molecule dynamics simulations to investigate the oligomerization of full-length hIAPP, employing multiple molecular systems of increasing number of peptides. We found that the oligomerization process was dynamic, involving frequent inter-oligomeric exchanges. On average, oligomers had more α-helices than β-sheets, consistent with ensemble-based experimental measurements. However, in ~4–6% independent simulations, β-rich oligomers expected as the fibrillization intermediates were observed, especially in the pentamer and hexamer simulations. These β-rich oligomers could adopt β-barrel conformations, recently postulated to be the toxic oligomer species but only observed computationally in the aggregates of short amyloid protein fragments. Free-energy analysis revealed high energies of these β-rich oligomers, supporting the nucleated conformational changes of oligomers in amyloid aggregation. β-barrel oligomers of full-length hIAPP with well-defined three-dimensional structures may play an important pathological role in T2D etiology and may be a therapeutic target for the disease.     

Cholinergic modulation of anaphylactic shock: plasma proteins influence

Cholinergic drugs can modulate anaphylactic shock and change lymphocyte functions. Plasma proteins modulate effects of muscarinic antagonists during anaphylactic shock. The present investigation was carried out to study the antianaphylactic activity of methacine (antagonist at muscarinic receptors) in combination with neostigmine (anticholinesterase drug). However, it is not known whether plasma proteins-albumin, C-reactive protein (CRP) and immunoglobulin G (IgG) - modify the effects of cholinergic drugs like methacine, serotonin (5-HT) level in the lymphoid organs and quantity of antibody-forming cells (AFC) in the spleen of guinea pigs during experimental anaphylactic shock. It was shown that administration of methacine with neostigmine (40 min and 15 min prior to shock induction, accordingly) at the pathochemical stage revokes shock development. By blocking cholinesterase endogenous acetylcholine is increased and methacine blocks muscarinic receptors and therewith unwanted side effects in the airways (bronchoconstriction) and heart (bradycardia). Administration of the combination of methacine with neostigmine at the immunological stage (guinea pig sensitization) does not affect the course of anaphylactic shock. Administration of methacine with IgG at the pathochemical stage of shock significantly decreases shock intensity, while administration of methacine with CRP or albumin has no influence on the shock. Administration of IgG or CRP (not albumin) at the immunological stage of shock and albumin or IgG (not CRP) at the pathochemical stage leads to reduction of the anaphylactic reaction. Application of methacine with neostigmine or IgG (effective combinations of drugs) results in normalization of antibody response in the spleen and 5-HT level in the lymphoid organs. Administration of methacine with CRP or albumin (ineffective combinations of drugs) leads to increase of antibody response in the spleen and 5-HT level in the lymphoid organs. Administration of hexamethonium or aceclidine aggravated anaphylactic shock reaction. Thus, the combination of methacine with neostigmine can regulate the pathochemical stage of shock and the 5-HT release. At the pathochemical stage of shock IgG increases the antianaphylactic activity of methacine, but albumin and CRP abolish it.     

ζ-Carotene: Generation and Quenching of Singlet Oxygen,Comparison with Phytofluene

Biochemistry (Moscow) - It is known that C40 carotenoids with a short chain of conjugated double bonds (CDB) (5 and 7, respectively) are universal precursors in the biosynthesis of colored...     

Synthesis and Antioxidant Ability of Novel Derivatives Based on para‐Coumaric Acid Containing Isobornyl Groups

A series of novel esters and amides was synthesized on the basis of para‐coumaric acid containing isobornyl groups in ortho‐positions relative to the phenolic hydroxy group. Antioxidant properties of the obtained compounds were evaluated and compared on in vitro models: radical‐scavenging ability, antioxidant activity on a substrate containing the lipids of animal brain, cytotoxicity of red blood cells, antioxidant and membrane‐protective properties on the model of oxidative red blood cells hemolysis. Statistically significant relationship was established between the antioxidant activity of the studied compounds in model system containing animal lipids and the parameters reflecting their antioxidant properties on the model of H₂O₂‐induced hemolysis of red blood cells. It was determined that an amide with a morpholine fragment has the highest antioxidant activity. The specified derivative significantly surpassed the reference substances (parent acid, BHT) and was not inferior to the effective antioxidant 2,6‐diisobornyl‐4‐methylphenol in terms of its properties.     

Early response of endothelial cells to flow is mediated by VE-cadherin

Endothelial cells are known to respond to flow onset by increasing actin turnover rate. Current models assume that an increase in the actin turnover rate should result in a rise in cell crawling speed. Here we report that confluent endothelial monolayer shows an unexpected behavior: cell crawling speed decreases by approximately 40% within the first 30 min of flow onset. A drop in crawling speed has not been observed in either subconfluent endothelial cells or in VE-cadherin-deficient cells. We found that flow onset caused an increase in the number of VE-cadherin-GFP molecules in the junctions and elicited changes in the cytoskeleton-associated fractions of alpha, beta -catenins and VE-cadherin. Flow application also increased the strength of interactions of endothelial cells with surfaces coated with recombinant VE-cadherin. These observations suggest that endothelial cell junctional proteins respond to flow transiently by increasing the strength of intercellular attachments early after flow onset and support the view on the active role of intercellular adhesions in mechanotransduction.     

Selectivity signatures of three isoforms of recombinant T-type Ca2+ channels

Voltage-gated Ca(2+) channels (VGCCs) are recognized for their superb ability for the preferred passage of Ca(2+) over any other more abundant cation present in the physiological saline. Most of our knowledge about the mechanisms of selective Ca(2+) permeation through VGCCs was derived from the studies on native and recombinant L-type representatives. However, the specifics of the selectivity and permeation of known recombinant T-type Ca(2+)-channel alpha1 subunits, Ca(v)3.1, Ca(v)3.2 and Ca(v)3.3, are still poorly defined. In the present study we provide comparative analysis of the selectivity and permeation Ca(v)3.1, Ca(v)3.2, and Ca(v)3.3 functionally expressed in Xenopus oocytes. Our data show that all Ca(v)3 channels select Ca(2+) over Na(+) by affinity. Ca(v)3.1 and Ca(v)3.2 discriminate Ca(2+), Sr(2+) and Ba(2+) based on the ion's effects on the open channel probability, whilst Ca(v)3.3 discriminates based on the ion's intrapore binding affinity. All Ca(v)3s were characterized by much smaller difference in the K(D) values for Na(+) current blockade by Ca(2+) (K(D1) approximately 6 microM) and for Ca(2+) current saturation (K(D2) approximately 2 mM) as compared to L-type channels. This enabled them to carry notable mixed Na(+)/Ca(2+) current at close to physiological Ca(2+) concentrations, which was the strongest for Ca(v)3.3, smaller for Ca(v)3.2 and the smallest for Ca(v)3.1. In addition to intrapore Ca(2+) binding site(s) Ca(v)3.2, but not Ca(v)3.1 and Ca(v)3.3, is likely to possess an extracellular Ca(2+) binding site that controls channel permeation. Our results provide novel functional tests for identifying subunits responsible for T-type Ca(2+) current in native cells.