Glutamate 85 and glutamate 228 contribute to the pH-response of the soluble form of chloride intracellular channel 1

The chloride intracellular channel protein, CLIC1, is synthesised as a soluble monomer that can reversibly bind membranes. Soluble CLIC1 is proposed to respond to the low pH found at a membrane surface by partially unfolding and restructuring into a membrane-competent conformation. This transition is proposed to be controlled by strategically located “pH-sensor” residues that become protonated at acidic pH. In this study, we investigate the role of two conserved glutamate residues, Glu85 in the N-domain and Glu228 in the C-domain, as pH-sensors. E85L and E228L CLIC1 variants were created to reduce pH sensitivity by permanently breaking the bonds these residues form. The structure and stability of each variant was compared to the wild type at both pH 7.0 and pH 5.5. Neither substitution significantly altered the structure but both decreased the conformational stability. Furthermore, E85L CLIC1 formed a urea-induced unfolding intermediate state at both pH 7 and pH 5.5 compared to wild-type and E228L CLIC1 which only formed the intermediate at pH 5.5. We conclude that Glu85 and Glu228 are two of the five pH-sensor residues of CLIC1 and contribute to the pH-response in different ways. Glu228 lowers the stability of the native state at pH 5.5, while Glu85 contributes both to the stability of the native state and to the formation of the intermediate state. By putting these interactions into the context of the three previously described CLIC1 pH-sensor residues, we propose a mechanism for the conversion of CLIC1 from the soluble state to the pre-membrane form.     

Zidovudine (azido dideoxythymidine) inhibits characteristic early alterations of lymphoid cell populations in retrovirus-induced murine AIDS

Using flow cytometry technology and multiparameter analyses, we report early and characteristic alterations in lymphoid cell profile in spleen and lymph nodes due to LP-BM5 retrovirus disease (murine AIDS (MAIDS)) and the effect of azido dideoxythymidine, a nucleoside inhibitor, on these changes. MAIDS has been characterized by rapid and profound lymphoproliferation accompanied by hypergammaglobulinemia and immunosuppression. As early as 2 wk postinfection, there is a selective depletion of CD8+ cells whereas the total number of CD4+ cells increases throughout the first 8 wk of infection although the frequency is relatively stable. These population changes were partially delayed by oral AZT therapy for 6 wk postinfection. Ly-6C (AL-21) is expressed on roughly 50% of CD4+ and CD8+ cells in C57BL/6 mice. In MAIDS, the residual population of CD8+ cells is primarily Ly-6C+. The CD4+ cells have a transient increase in ratio of Ly-6C+/Ly-6C- cells at 2 wk postinfection but by 6 wk are primarily Ly-6C-. There was an increase in both the total number and percentage of Mac 1+ cells and a selective depletion of certain splenic B cell subpopulations. Azido dideoxythymidine delays these early population changes.     

The utility of wing morphometrics for assigning type specimens to cryptic bumblebee species

Since the beginning of taxonomy, species have been described based on morphology, but the advent of using semio-chemicals and genetics has led to the discovery of cryptic species (i.e. morphologically similar species). When a new cryptic species is described, earlier type specimens have to be re-evaluated, although this process can be challenging as only nondestructive methods ought to be used in order to preserve the integrity of the type specimens. Methods should allow comparison with recently collected specimens clustered based on chemical, ethological and/or genetic traits with old specimens (i.e. type specimens) where only morphological traits are available. Here we develop a method based on geometric morphometric analyses of wing shape for a taxonomically challenging group of bumblebees, the subgenus Alpinobombus Skorikov. We consider nine monophyletic taxa (including several cryptic species) to assess the accuracy of this method to discriminate the taxa based on their wing shape and then to attribute type specimens using a leave-one-out cross-validation procedure. We show that, for these bees, wing shape is taxon-specific, except for two sister taxa for which the species status is still debated. Moreover, for most of the taxa, type specimens were correctly attributed with high posterior probabilities of attribution, except for a few type specimens corresponding to the same two sister taxa where taxa delimitation based on wing shape was previously the subject of discussion. Our study highlights the potential of geometric morphometric analyses to help in the re-attribution of type specimens when the existence of cryptic species is revealed.     

beta, a novel repetitive DNA element associated with tRNA genes in the pathogenic yeast Candida albicans

We have identified a novel 399 bp repetitive DNA element (which we designate beta  ) 9 bp upstream of a seryl-tRNA_CAG gene in the genome of Candida albicans . There are two copies of the seryl-tRNA_CAG gene, one on each homologue of chromosome VI, and the beta element is found upstream of one copy of the gene in C. albicans strain 2005E. The beta element is not present upstream of either copy of the seryl-tRNA_CAG gene in eight other laboratory strains of C. albicans tested, but was detected in this location in several fresh clinical isolates. Southern blot analysis indicated that there are approximately eight copies of the beta element per diploid C. albicans genome and that it is a mobile element, being present on at least two different chromosomes. Three unique genomic DNA clones containing the beta element were isolated from strain 2005E; in each case, a different tRNA gene was found immediately adjacent to the beta element. Three new tRNA genes from C. albicans have thus been identified: tRNA^Asp, tRNA^Ala and tRNA^Ile. The beta element shows no significant sequence homology to other known prokaryotic or eukaryotic repetitive elements, although an 8 bp repeat at the 3' end of the element is identical to that of the Ty3 retrotransposable element of Saccharomyces cerevisiae . We propose that the beta element is a solo long terminal repeat (LTR) sequence of a Ty3/gypsy-like transposable element in C. albicans that is closely associated with tRNA genes.     

Commentary: Chiral Symmetry-Breaking by Crystallization

Origins of Life and Evolution of Biospheres -     

Direct Regulation of Osteocytic Connexin 43 Hemichannels through AKT Kinase Activated by Mechanical Stimulation

Connexin (Cx) 43 hemichannels in osteocytes are thought to play a critical role in releasing bone modulators in response to mechanical loading, a process important for bone formation and remodeling. However, the underlying mechanism that regulates the opening of mechanosensitive hemichannels is largely unknown. We have recently shown that Cx43 and integrin α5 interact directly with each other, and activation of PI3K appears to be required for Cx43 hemichannel opening by mechanical stimulation. Here, we show that mechanical loading through fluid flow shear stress (FFSS) increased the level of active AKT, a downstream effector of PI3K, which is correlated with the opening of hemichannels. Both Cx43 and integrin α5 are directly phosphorylated by AKT. Inhibition of AKT activation significantly reduced FFSS-induced opening of hemichannels and disrupted the interaction between Cx43 and integrin α5. Moreover, AKT phosphorylation on Cx43 and integrin α5 enhanced their interaction. In contrast to the C terminus of wild-type Cx43, overexpression of the C-terminal mutant containing S373A, a consensus site previously shown to be phosphorylated by AKT, failed to bind with α5 and hence could not inhibit hemichannel opening. Together, our results suggest that AKT activated by FFSS directly phosphorylates Cx43 and integrin α5, and Ser-373 of Cx43 plays a predominant role in mediating the interaction between these two proteins and Cx43 hemichannel opening, a crucial step to mediate the anabolic function of mechanical loading in the bone.     

Physiographic and climatic events in the Chihuahuan Desert lead to the speciation and distinct demographic patterns of two sister Sceloporus lizards

The biogeographic history of the Chihuahuan Desert is known to be complex, and there is evidence of the effects of physiographic and climatic events in species diversification and demographic population changes in many taxa. Here, using DNA sequence data, we studied the influence of the physiographic and climatic events that occurred in the Chihuahuan Desert during the Pliocene–Pleistocene transition on the speciation and evolutionary history of the sister lizard species Sceloporus cyanostictus and S. gadsdeni. First, based on mtDNA and nDNA sequences, we estimated the divergence times of the sister species. Then, based on mtDNA sequences, we investigated the demographic history of both species within a phylogeographic framework. The divergence time was inferred to be 1.48 Mya, date that corresponds to the existence of a large lake in the Mapimian subprovince, between the current geographic locations of S. cyanostictus and S. gadsdeni. This lake could have acted as a barrier, leading to the speciation of both species. For the demographic history of the two species, we identified two distinct patterns: the population expansion of S. gadsdeni within the Last Glacial Maximum and the potential population decline of S. cyanostictus. Our results can be used as a guide for the study of other aspects that could be critical to developing conservation actions that ensure the survival of not only S. gadsdeni and S. cyanostictus, but also other co‐occurring lizard species.