Bestrophin-1 enables Ca2+-activated Cl- conductance in epithelia

Epithelial cells express calcium-activated Cl(-) channels of unknown molecular identity. These Cl(-) channels play a central role in diseases such as secretory diarrhea, polycystic kidney disease, and cystic fibrosis. The family of bestrophins has been suggested to form calcium-activated Cl(-) channels. Here, we demonstrate molecular and functional expression of bestrophin-1 (BEST1) in mouse and human airways, colon, and kidney. Endogenous calcium-activated whole cell Cl(-) currents coincide with endogenous expression of the Vmd2 gene product BEST1 in murine and human epithelial cells, whereas calcium-activated Cl(-) currents are absent in epithelial tissues lacking BEST1 expression. Blocking expression of BEST1 with short interfering RNA or applying an anti-BEST1 antibody to a patch pipette suppressed ATP-induced whole cell Cl(-) currents. Calcium-dependent Cl(-) currents were activated by ATP in HEK293 cells expressing BEST1. Thus, BEST1 may form the Ca2+-activated Cl(-) current, or it may be a component of a Cl(-) channel complex in epithelial tissues.     

Conformational changes in switch I of EF‐G drive its directional cycling on and off the ribosome

We have trapped elongation factor G (EF-G) from Escherichia coli in six, functionally defined states, representing intermediates in its unidirectional catalytic cycle, which couples GTP hydrolysis to tRNA–mRNA translocation in the ribosome. By probing EF-G with trypsin in each state, we identified a substantial conformational change involving its conserved switch I (sw1) element, which contacts the GTP substrate. By attaching FeBABE (a hydroxyl radical generating probe) to sw1, we could monitor sw1 movement (by ∼20 Å), relative to the 70S ribosome, during the EF-G cycle. In free EF-G, sw1 is disordered, particularly in GDP-bound and nucleotide-free states. On EF-G•GTP binding to the ribosome, sw1 becomes structured and tucked inside the ribosome, thereby locking GTP onto EF-G. After hydrolysis and translocation, sw1 flips out from the ribosome, greatly accelerating release of GDP and EF-G from the ribosome. Collectively, our results support a central role of sw1 in driving the EF-G cycle during protein synthesis.     

Phylogenomic analyses support the monophyly of Taphrinomycotina, including Schizosaccharomyces fission yeasts

Several morphologically dissimilar ascomycete fungi includingSchizosaccharomyces, Taphrina, Saitoella, Pneumocystis, andNeolecta have been grouped into the taxon Taphrinomycotina (Archiascomycotaor Archiascomycotina), originally based on rRNA phylogeny. Theseanalyses lack statistically significant support for the monophylyof this grouping, and although confirmed by more recent multigeneanalyses, this topology is contradicted by mitochondrial phylogenies.To resolve this inconsistency, we have assembled phylogenomicmitochondrial and nuclear data sets from four distantly relatedtaphrinomycotina taxa: Schizosaccharomyces pombe, Pneumocystiscarinii, Saitoella complicata, and Taphrina deformans. Our phylogenomicanalyses based on nuclear data (113 proteins) conclusively supportthe monophyly of Taphrinomycotina, diverging as a sister groupto Saccharomycotina + Pezizomycotina. However, despite the improvedtaxon sampling, Taphrinomycotina continue to be paraphyleticwith the mitochondrial data set (13 proteins): Schizosaccharomycesspecies associate with budding yeasts (Saccharomycotina) andthe other Taphrinomycotina group as a sister group to Saccharomycotina+ Pezizomycotina. Yet, as Schizosaccharomyces and Saccharomycotinaspecies are fast evolving, the mitochondrial phylogeny may beinfluenced by a long-branch attraction (LBA) artifact. Afterremoval of fast-evolving sequence positions from the mitochondrialdata set, we recover the monophyly of Taphrinomycotina. Ourcombined results suggest that Taphrinomycotina is a legitimatetaxon, that this group of species diverges as a sister groupto Saccharomycotina + Pezizomycotina, and that phylogeneticpositioning of yeasts and fission yeasts with mitochondrialdata is plagued by a strong LBA artifact.     

Analysis of structure and function of the giant protein Pf332 in Plasmodium falciparum

Virulence of Plasmodium falciparum , the most lethal parasitic disease in humans, results in part from adhesiveness and increased rigidity of infected erythrocytes. Pf332 is trafficked to the parasite-infected erythrocyte via Maurer's clefts, structures for protein sorting and export in the host erythrocyte. This protein has a domain similar to the Duffy-binding-like (DBL) domain, which functions by binding to receptors for adherence and invasion. To address structure of the Pf332 DBL domain, we expressed this region, and validated its fold on the basis of the disulphide bond pattern, which conformed to the generic pattern for DBL domains. The modelled structure for Pf332 DBL had differences compared with the erythrocyte-binding region of the αDBL domain of Plasmodium knowlesi Duffy-binding protein (Pkα-DBL). We addressed the function of Pf332 by constructing parasites that either lack expression of the protein or express an altered form. We found no evidence that Pf332 is involved in cytoadhesion or merozoite invasion. Truncation of Pf332 had a significant effect on deformability of the P. falciparum -infected erythrocyte, while loss of the full protein deletion did not. Our data suggest that Pf332 may contribute to the overall deformability of the P. falciparum -infected erythrocyte by anchoring and scaffolding.     

Mutations in LOXHD1, an Evolutionarily Conserved Stereociliary Protein, Disrupt Hair Cell Function in Mice and Cause Progressive Hearing Loss in Humans

Hearing loss is the most common form of sensory impairment in humans and is frequently progressive in nature. Here we link a previously uncharacterized gene to hearing impairment in mice and humans. We show that hearing loss in the ethylnitrosourea (ENU)-induced samba mouse line is caused by a mutation in Loxhd1. LOXHD1 consists entirely of PLAT (polycystin/lipoxygenase/α-toxin) domains and is expressed along the membrane of mature hair cell stereocilia. Stereociliary development is unaffected in samba mice, but hair cell function is perturbed and hair cells eventually degenerate. Based on the studies in mice, we screened DNA from human families segregating deafness and identified a mutation in LOXHD1, which causes DFNB77, a progressive form of autosomal-recessive nonsyndromic hearing loss (ARNSHL). LOXHD1, MYO3a, and PJVK are the only human genes to date linked to progressive ARNSHL. These three genes are required for hair cell function, suggesting that age-dependent hair cell failure is a common mechanism for progressive ARNSHL.     

Transport of glutathione transferase-fold structured proteins into living cells

Glutathione transferases are a family of enzymes that are traditionally known to contribute to the phase II class of detoxification reactions. However, a novel property of the Schistosoma japonicum glutathione transferase (Sj.GST26) involves its translocation from the external medium into a variety of different cell types. Here we explore the efficiency and mechanism of cell entry for this class of protein. Using flow cytometry and confocal microscopy, we have examined the internalisation of Sj.GST26 into live cells under a variety of conditions designed to shed light on the mode of cellular uptake. Our results show that Sj.GST26 can effectively enter cells through an energy-dependent event involving endocytosis. More specifically, Sj.GST26 was found to colocalise with transferrin within the cell indicating that the endocytosis process involves clathrin-coated pits. A comprehensive study into the cellular internalisation of proteins from other classes within the GST structural superfamily has also been conducted. These experiments suggest that the ‘GST-fold’ structural motif influences cellular uptake, which presents a novel glimpse into an unknown aspect of GST function.