Analysis of seasonal fluctuations in the Lotka-Volterra model

A modification of the Lotka-Volterra model was proposed. The modification takes into account the factor of seasonal fluctuations in a "predator-prey" model. In this modification, interactions between species in summer are described by the Lotka-Volterra equations; in winter, individuals of both species extinct. This generalization makes the classic model unrough, which substantially extends the field of its application. The results of numerical simulation illustrate the statement formulated above.     

Enhancement of the Bactericidal Effect of Antibiotics by Inhibition of Enzymes Involved in Production of Hydrogen Sulfide in Bacteria

Molecular Biology - Counteraction of the origin and distribution of multidrug-resistant pathogens responsible for intra-hospital infections is a worldwide issue in medicine. In this brief review,...     

Emergence of acetylcholine resistance and loss of rhythmic activity associated with the development of hypertension,obesity, and type 2 diabetes

The aim of this work was to study the influence of aging, obesity, metabolic syndrome (MS), hypertension (HT), and type 2 diabetes (T2D) on the endogenous rhythmic activity and the development acetylcholine resistance in aorta rings of male rats. T2D was produced by a free access to fat (lard). It was shown that phenylephrine (PE) or 5-hydroxytryptamine (5-HT) induces two types of rhythmic contractions: with periods T ₁ = 3–10 s and T ₂ = 50–70 s and amplitudes A ₁ = 1–5% and A ₂ = 20–40% of the maximal contraction force (F _max), respectively. Such periodic modes can be caused by the operation of two known positive feedback loops (PFL) based on the Ca²⁺-induced activation of IP3 receptor (IP3R) or phospholipase C PFL1 and PFL2, respectively, and are not eliminated by L-NAME. Slow rhythmic activity induced by acetylcholine (Ach) with period T ₃ = 7–20 min and amplitude A ₃ = 20–30% of F _max was observed only in young animals (under 6 months) and can be determined by the operation of PFL3, involving Ca²⁺, NO, kinase G, cADP-ribose, and the ryanodine receptor (RyR). Fast mode of contractions (T ₁, A ₁) is maintained regardless of age and the presence of MS and HT (140 mm Hg and higher) and disappears only at later stages of the T2D development. Probability of intermediate mode of contractions (T ₂, A ₂) decreases to 0.20–0.25 at the age of 14–16 months or during the development of HT and MS. In these circumstances, Ach could cause relaxation of preconstricted rings only to 40 and 60% of F _max, respectively. At the stages of the T2D development characterized by high values of arterial pressure (above 150 mm Hg) and of the glucose (10–12 mM), ammonium (120–180 μM), and blood lipid levels, as well as by liver dysfunction (fibrosis/cirrhosis), the rhythmic activity of any type is lost and dysfunction of the initial part of the signaling cascade with the participation of PFL3 is manifested by the absence of responses to Ach or L-NAME. Coenzyme NAD (agonist of the P2Y receptors, К⁺ channel activator and a precursor of cADP-ribose) can exert a partial relaxation of aorta rings from healthy animals and animals with MS. Nicotinamide (product and an inhibitor of ADP-ribosyl cyclase) and SNP (donor of NO) produce an effective relaxation of aorta rings from healthy animals and animals with T2D. Relaxing effect of nicotinamide may suggest a tandem operation of IP3R and RyR in the control of intracellular Ca²⁺ stores in vascular cells.     

The effect of electric field on the spatial-time patterns in the reaction-diffusion system

A model of electrodiffusion processes in the vicinity of cell membrane was developed. The model takes into account chemical reactions, Coulomb interactions between charged particles and the effect of external electric field. It was concluded that the applied electric field can change the characteristics of space-time patterns in the system. Dissipative structures slowly move and this is accompanied by a change in the number of structure elements. The characteristic equation includes odd powers of the wavenumber, which can lead to the appearance of soliton-like structures. The dissipative structures can appear not only due to the Turing diffusion instability but due to the disperse instability under electric field the applied.     

An N-terminal, 830 residues intrinsically disordered region of the cytoskeleton-regulatory protein supervillin contains Myosin II- and F-actin-binding sites

Supervillin, the largest member of the villin/gelsolin family, is a cytoskeleton regulating, peripheral membrane protein. Supervillin increases cell motility and promotes invasive activity in tumors. Major cytoskeletal interactors, including filamentous actin and myosin II, bind within the unique supervillin amino terminus, amino acids 1–830. The structural features of this key region of the supervillin polypeptide are unknown. Here, we utilize circular dichroism and bioinformatics sequence analysis to demonstrate that the N-terminal part of supervillin forms an extended intrinsically disordered region (IDR). Our combined data indicate that the N-terminus of human and bovine supervillin sequences (positions 1–830) represents an IDR, which is the largest IDR known to date in the villin/gelsolin family. Moreover, this result suggests a potentially novel mechanism of regulation of myosin II and F-actin via the intrinsically disordered N-terminal region of hub protein supervillin.     

SECIS elements in the coding regions of selenoprotein transcripts are functional in higher eukaryotes

Expression of selenocysteine (Sec)-containing proteins requires the presence of a cis-acting mRNA structure, called selenocysteine insertion sequence (SECIS) element. In bacteria, this structure is located in the coding region immediately downstream of the Sec-encoding UGA codon, whereas in eukaryotes a completely different SECIS element has evolved in the 3'-untranslated region. Here, we report that SECIS elements in the coding regions of selenoprotein mRNAs support Sec insertion in higher eukaryotes. Comprehensive computational analysis of all available viral genomes revealed a SECIS element within the ORF of a naturally occurring selenoprotein homolog of glutathione peroxidase 4 in fowlpox virus. The fowlpox SECIS element supported Sec insertion when expressed in mammalian cells as part of the coding region of viral or mammalian selenoproteins. In addition, readthrough at UGA was observed when the viral SECIS element was located upstream of the Sec codon. We also demonstrate successful de novo design of a functional SECIS element in the coding region of a mammalian selenoprotein. Our data provide evidence that the location of the SECIS element in the untranslated region is not a functional necessity but rather is an evolutionary adaptation to enable a more efficient synthesis of selenoproteins.     

The difference between protein structures that are obtained by X-ray analysis and magnetic resonance spectroscopy

We have analyzed the proteins whose structures were determined both by X-ray analysis (X-ray) and nuclear magnetic resonance (NMR) on condition that these structures do not differ greatly when spatially superimposed on each other (61 pairs of protein structures). Atom-atomic contacts (contact distances varied from 2 to 8 A) have been analyzed and it has been found that NMR structures (in comparison with X-ray ones) have more contacts in the range below 3.5 A and above 5.5 A. In the case of residue-residue contacts NMR structures have more contacts below 3 A and between 4.5 and 6.5 A. At all the other contact distances analyzed the X-ray structures have more contacts. The difference in the number of atom-atomic and residue-residue contacts is greater for internal residues, that are concealed from water, as compared to the surface residues. The other, not less important difference deals with the number of hydrogen bonds in the main chain: it is larger for the X-ray structures. The correlation between the hydrogen bonds identified in the structures obtained by both methods is no more than 32%. The consideration of a complete set of protein structures obtained by NMR results in the fact that the number of hydrogen bonds grows 1.2 times as compared to those obtained with the X-ray analysis, whereas the correlation increases only by 65%. We have also demonstrated that alpha-helices in the NMR structures are more distorted in comparison with the ideal alpha-helix, than alpha-helices in the X-ray structures.     

Numerical study of the stability of some autowave solutions in a mathematical model of blood clotting

The stability of some types of solution for a set of equations representing a blood clotting model is examined using numerical methods of solving perturbation problems and the apparatus of adjoint equations. It is concluded that spiral waves are stable in this system, whereas traveling pulses are unstable at parameters corresponding to a chaotic regime in the punctual problem.     

Eukaryotic selenoproteins and selenoproteomes

Selenium is an essential trace element for which both beneficial and toxic effects in human health have been described. It is now clear that the importance of having adequate amounts of this micronutrient in the diet is primarily due to the fact that selenium is required for biosynthesis of selenocysteine, the twenty first naturally occurring amino acid in protein. In this review, we provide an overview of eukaryotic selenoproteins and selenoproteomes, which are sets of selenoproteins in these organisms. In eukaryotes, selenoproteins show a mosaic occurrence, with some organisms, such as vertebrates and algae, having dozens of these proteins, while other organisms, such as higher plants and fungi, having lost all selenoproteins during evolution. We also discuss selenoprotein functions and evolutionary trends in the use of these proteins in eukaryotes. Functional analysis of selenoproteins is critical for better understanding of the role of selenium in human health and disease.