Adrenergic receptor density in brown adipose tissue of active and hibernating hamsters and ground squirrels

The ligand-binding characteristics (B(max) and K(D)) of alpha(1)- and beta(1)/beta(2)-adrenoceptors were investigated in membranes prepared from brown adipose tissue (BAT) of warm-acclimated, cold-acclimated, hibernating and arousing ground squirrels (Spermophillus undulatus) and hamsters (Mesocricetus auratus) by specific binding of [(3)H]prazosin and [(3)H]CGP-12177, respectively. The physiological state did not change the affinity for the adrenoceptors in the BAT of ground squirrels and hamsters. There was a significant decrease in alpha(1)-receptor density in arousing ground squirrels and a significant decrease in beta(1)/beta(2) density in hibernating ground squirrels. The level of alpha(1)-receptors was in all conditions higher than that of beta(1)/beta(2) receptors. The results indicate a possible change in balance of adrenoceptor density in the processes of cold acclimation, hibernation and arousal. The balance between the various adrenoceptor subtypes may be important for the final effect of catecholamines in BAT in different physiological states.     

Effects of amino acid composition, finite size of proteins, and sparse statistics on distance-dependent statistical pair potentials

Statistical distance dependent pair potentials are frequently used in a variety of folding, threading, and modeling studies of proteins. The applicability of these types of potentials is tightly connected to the reliability of statistical observations. We explored the possible origin and extent of false positive signals in statistical potentials by analyzing their distance dependence in a variety of randomized protein-like models. While on average potentials derived from such models are expected to equal zero at any distance, we demonstrate that systematic and significant distortions exist. These distortions originate from the limited statistical counts in local environments of proteins and from the limited size of protein structures at large distances. We suggest that these systematic errors in statistical potentials are connected to the dependence of amino acid composition on protein size and to variation in protein sizes. Additionally, atom-based potentials are dominated by a false positive signal that is due to correlation among distances measured from atoms of one residue to atoms of another residue. The significance of residue-based pairwise potentials at various spatial pair separations was assessed in this study and it was found that as few as approximately 50% of potential values were statistically significant at distances below 4 A, and only at most approximately 80% of them were significant at larger pair separations. A new definition for reference state, free of the observed systematic errors, is suggested. It has been demonstrated to generate statistical potentials that compare favorably to other publicly available ones.     

Widespread positive selection in the photosynthetic Rubisco enzyme

Background  

Rubisco enzyme catalyzes the first step in net photosynthetic CO₂ assimilation and photorespiratory carbon oxidation and is responsible for almost all carbon fixation on Earth. The large subunit of Rubisco is encoded by the chloroplast rbcL gene, which is widely used for reconstruction of plant phylogenies due to its conservative nature. Plant systematicists have mainly used rbcL paying little attention to its function, and the question whether it evolves under Darwinian selection has received little attention. The purpose of our study was to evaluate how common is positive selection in Rubisco among the phototrophs and where in the Rubisco structure does positive selection occur.     

Rab27b regulates mast cell granule dynamics and secretion

The Rab GTPase family regulates membrane domain organization and vesicular transport pathways. Recent studies indicate that one member of the family, Rab27a, regulates transport of lysosome-related organelles in specialized cells, such as melanosomes and lytic granules. Very little is known about the related isoform, Rab27b. Here we used genetically modified mice to study the involvement of the Rab27 proteins in mast cells, which play key roles in allergic responses. Both Rab27a and Rab27b isoforms are expressed in bone marrow-derived mast cells (BMMC) and localize to secretory granules. Nevertheless, secretory defects as measured by beta-hexosaminidase release in vitro and passive cutaneous anaphylaxis in vivo were found only in Rab27b and double Rab27 knockout (KO) mice. Immunofluorescence studies suggest that a subset of Rab27b and double Rab27-deficient BMMCs exhibit mild clustering of granules. Quantitative analysis of live-cell time-lapse imaging revealed that BMMCs derived from double Rab27 KO mice showed almost 10-fold increase in granules exhibiting fast movement (>1.5 microm/s), which could be disrupted by nocodazole. These results suggest that Rab27 proteins, particularly Rab27b, play a crucial role in mast cell degranulation and that their action regulates the transition from microtubule to actin-based motility.     

AZT 5'-Cholinephosphate as an anti-HIV agent: the study of biochemical properties and metabolic transformations using its 32P-labelled counterpart

Biochemical and metabolic transformations of 3'-azido-3'-deoxythymidine 5'-choline phosphate (1) were studied using its 32P-labelled counterpart for the evaluation of possible reasons for its enhanced anti-HIV activity. An effective synthesis of 32P-labelled 1 with a specific activity >1,000 Ci/mmol was developed by esterification of 32P-phosphoric acid with choline in the presence of BrCN followed by the coupling of the resulting choline phosphate with 3'-azido-3'-deoxythymidine (AZT). Chemical and enzymatic stabilities of 1 as well as the dynamics of penetration through HL-60 cell membranes were studied at the concentrations comparable to its antiviral concentrations. The products of intracellular transformations of the studied nucleotide were identified.     

Two hypotheses of the evolution of endemic sponges in Lake Baikal (Lubomirskiidae)

Complete and nearly complete mtDNA genome sequences were used to resolve differences between two palaeontology‐based hypotheses on timing of the origin of the Baikal endemic sponge family Lubomirskiidae (Haplosclerida, Demospongiae). Bayesian ratio test, when coupled with estimates of substitution rates based on known palaeontological findings, provided strong evidence for the Miocene origin over the Late Oligocene one. The common ancestor of the present day sponges in Lake Baikal diverged about 2,3 million years ago (Ma), while Lubomirskia baicalensis, Rezinkovia echinata, Baikalospongia intermedia profundalis and B. bacillifera split in the Pleistocene about 0,7 Ma. A phylogenetic analysis within the family suggested that speciation may have coincided with the occurrence of cold climatic conditions. We argue that the cause of speciation may be niche splitting due to temperature, depth and possibly feeding preferences.