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.     

Wnt directs the endosomal flux of LDL-derived cholesterol and lipid droplet homeostasis

The Wnt pathway, which controls crucial steps of the development and differentiation programs, has been proposed to influence lipid storage and homeostasis. In this paper, using an unbiased strategy based on high-content genome-wide RNAi screens that monitored lipid distribution and amounts, we find that Wnt3a regulates cellular cholesterol. We show that Wnt3a stimulates the production of lipid droplets and that this stimulation strictly depends on endocytosed, LDL-derived cholesterol and on functional early and late endosomes. We also show that Wnt signaling itself controls cholesterol endocytosis and flux along the endosomal pathway, which in turn modulates cellular lipid homeostasis. These results underscore the importance of endosome functions for LD formation and reveal a previously unknown regulatory mechanism of the cellular programs controlling lipid storage and endosome transport under the control of Wnt signaling.