Atomic Force Microscopy in Imaging of Viruses and Virus-Infected Cells

Summary: Atomic force microscopy (AFM) can visualize almost everything pertinent to structural virology and at resolutions that approach those for electron microscopy (EM). Membranes have been identified, RNA and DNA have been visualized, and large protein assemblies have been resolved into component substructures. Capsids of icosahedral viruses and the icosahedral capsids of enveloped viruses have been seen at high resolution, in some cases sufficiently high to deduce the arrangement of proteins in the capsomeres as well as the triangulation number (T). Viruses have been recorded budding from infected cells and suffering the consequences of a variety of stresses. Mutant viruses have been examined and phenotypes described. Unusual structural features have appeared, and the unexpectedly great amount of structural nonconformity within populations of particles has been documented. Samples may be imaged in air or in fluids (including culture medium or buffer), in situ on cell surfaces, or after histological procedures. AFM is nonintrusive and nondestructive, and it can be applied to soft biological samples, particularly when the tapping mode is employed. In principle, only a single cell or virion need be imaged to learn of its structure, though normally images of as many as is practical are collected. While lateral resolution, limited by the width of the cantilever tip, is a few nanometers, height resolution is exceptional, at approximately 0.5 nm. AFM produces three-dimensional, topological images that accurately depict the surface features of the virus or cell under study. The images resemble common light photographic images and require little interpretation. The structures of viruses observed by AFM are consistent with models derived by X-ray crystallography and cryo-EM.     

Dependence of cordycepin inhibition of heterogeneous nuclear RNA biosynthesis in rat brain on the size of the poly(A) segments

A study was made of the effect of cordicepin on the biosynthesis of rat brain heterogeneous nuclear RNA (hnRNA) fractions, such as poly(A-)hnRNA, oligo(A+)hnRNA and poly(A+)hnRNA differing in the size of poly(A)-segments. Cordicepin was shown to inhibit the biosynthesis of poly(A+)hnRNA alone. However, small doses of the antibiotic do not virtually inhibit the biosynthesis of hnRNA with shorter segments of poly(A). At the same time they inhibit the biosynthesis of hnRNA containing long chains of poly(A) in the 3'-end. A possible molecular mechanism of the phenomenon reviewed is under discussion.     

Aza-β-amino acid containing peptidomimetics as cAMP-dependent protein kinase substrates

Peptidomimetic analogs of the peptide RRASVA, known as the “minimal substrate” of the catalytic subunit of the cAMP-dependent protein kinase (PKA), were synthesized by consecutive replacement of natural amino acids by their aza-β³ analogs. The peptidomimetics were tested as PKA substrates and the kinetic parameters of the phosphorylation reaction were determined. It was found that the interaction of these peptidomimetics with the enzyme active center was sensitive to the location of the backbone modification, while the maximal rate of the reaction was practically not affected by the structure of substrates. The pattern of molecular recognition of peptidomimetics was in agreement with the results of structure modeling and also with the results of computational docking study of peptide and peptidomimetic substrates with the active center of PKA. It was concluded that the specificity determining factors which govern substrate recognition by the enzyme should be grouped along the phosphorylatable substrate, and such clustering might open new perspectives for pharmacophore design of peptides and peptide-like ligands.     

Vendian-Cambrian tidal and sabkha facies of the Siberian platform

Summary The Vendian-Cambrian interval on the Siberian Platform contains thick carbonate and evaporite sequences formed in extensive shallow-water basins. The carbonate sequences are characterized by a cyclic composition. Finegrained dolomites, undulated algal dolomites, flat pebble conglomerates, storm breccias and solution-collapse breccias form the base of each cycle. These rocks are characterized by an increased clay content which can be high enough to form argillites. Short sedimentation breaks reflected by mudcracks or silicification horizons are present as well as small cross-bedded tidal channels. Peloidal grainstones with algal overgrowth dominate in the central parts of the cycles. These members are often recrystallized and dolomitized. Micritic dolomites, undulous laminated dolomites, storm breccias and columnar stromatolites with abundant mud cracks form the upper members of the cycles. These sequences are free of clay but contain abundant anhydrite crystals and nodules. In the uppermost parts of some cycles massive layered anhydrite beds are present. The cycles vary in thickness, but usually they are between 15 and 20 m thick. The lower cycle member documents extreme shallow-water deposits. They formed in tidal and partially also supratidal zones not far from the mainland, from where fine clayey material was washed in. These parts of the sequence reflect a slow transgression. The central member of a cycle was deposited during the maximal transgression in a shallow basin with normal salinity and rather active hydrodynamics. Sedimentation of the upper part of the cycles reflects a regression stage (tidal and especially sabkha environments). The final layered anhydrite beds formed most probably in relict lakes on the sabkha plain. During sea-level falls some sequences of the central parts of the cycles were subaerially exposed and underwent partial dolomitization. The Vendian-Cambrian sabkhas are partly comparable with their recent counterparts.     

The Intracellular Calcium Kinetics and Action Potential in the Ventricular Myocardium of Spontaneously Hypertensive ISIAH Rats

Biophysics - Here, we show the dependence of intracellular calcium kinetics and the duration of the action potential of cardiomyocytes on an animal’s age in multicellular preparations of the...     

The mechanism of cathode reduction of oxygen in a carbon carrier-laccase system

The influence of temperature, oxygen pressure and inhibitors of laccase on the dioxygen electroreduction reaction has been examined at different solution pH. On the basis of obtained data, a reaction mechanism including electron transfer from the enzyme active site to the oxygen molecule is suggested as the slow step.     

Sorbents with immobilized glycopeptide antibiotics for separating optical isomers by high-performance liquid chromatography

Chiral sorbents for HPLC separation of optical isomers carrying glycopeptide antibiotics (eremomycin or its eremosaminyl aglycon, ristomycin, or vancomycin) fixed onto the surface of silica gel have been synthesized. The patterns of the retention and separation of profen isomers and their dependence on the nature of the chiral selector and the eluant composition have been studied. The sorbents were shown to be highly enantiospecific in separating the isomers of α-amino-, α-hydroxy-, and α-methylphenylcarboxylic acids (profens)