Dynamic functional assembly of the Torsin AAA+ ATPase and its modulation by LAP1

Torsins are essential AAA+ proteins of the endoplasmic reticulum and nuclear envelope (NE). We now show that Torsin homo-oligomers are essential for Torsin function at the NE and that Torsin’s oligomeric state is negatively modulated by its cofactors, representing a novel regulation mechanism for AAA+ proteins.

TorsinA is an essential AAA+ ATPase requiring LAP1 or LULL1 as cofactors. The dynamics of the Torsin/cofactor system remain poorly understood, with previous models invoking Torsin/cofactor assemblies with fixed stoichiometries. Here we demonstrate that TorsinA assembles into homotypic oligomers in the presence of ATP. Torsin variants mutated at the “back” interface disrupt homo-oligomerization but still show robust ATPase activity in the presence of its cofactors. These Torsin mutants are severely compromised in their ability to rescue nuclear envelope defects in Torsin-deficient cells, suggesting that TorsinA homo-oligomers play a key role in vivo. Engagement of the oligomer by LAP1 triggers ATP hydrolysis and rapid complex disassembly. Thus the Torsin complex is a highly dynamic assembly whose oligomeric state is tightly controlled by distinctively localized cellular cofactors. Our discovery that LAP1 serves as a modulator of the oligomeric state of an AAA+ protein establishes a novel means of regulating this important class of oligomeric ATPases.

Torsin ATPases: Harnessing Dynamic Instability for Function

Torsins are essential, disease-relevant AAA+ (ATPases associated with various cellular activities) proteins residing in the endoplasmic reticulum and perinuclear space, where they are implicated in a variety of cellular functions. Recently, new structural and functional details about Torsins have emerged that will have a profound influence on unraveling the precise mechanistic details of their yet-unknown mode of action in the cell. While Torsins are phylogenetically related to Clp/HSP100 proteins, they exhibit comparatively weak ATPase activities, which are tightly controlled by virtue of an active site complementation through accessory cofactors. This control mechanism is offset by a TorsinA mutation implicated in the severe movement disorder DYT1 dystonia, suggesting a critical role for the functional Torsin-cofactor interplay in vivo. Notably, TorsinA lacks aromatic pore loops that are both conserved and critical for the processive unfolding activity of Clp/HSP100 proteins. Based on these distinctive yet defining features, we discuss how the apparent dynamic nature of the Torsin-cofactor system can inform emerging models and hypotheses for Torsin complex formation and function. Specifically, we propose that the dynamic assembly and disassembly of the Torsin/cofactor system is a critical property that is required for Torsins' functional roles in nuclear trafficking and nuclear pore complex assembly or homeostasis that merit further exploration. Insights obtained from these future studies will be a valuable addition to our understanding of disease etiology of DYT1 dystonia.

Molecular mechanism of membrane binding of the GRP1 PH domain

The pleckstrin homology (PH) domain of the general receptor of phosphoinositides 1 (GRP1) protein selectively binds to a rare signaling phospholipid, phosphatidylinositol (3,4,5)-trisphosphate (PIP3), in the membrane. The specific PIP3 lipid docking of GRP1 PH domain is essential to protein cellular function and is believed to occur in a stepwise process, electrostatic-driven membrane association followed by the specific PIP3 binding. By a combination of all-atom molecular dynamics (MD) simulations, coarse-grained analysis, electron paramagnetic resonance (EPR) membrane docking geometry, and fluorescence resonance energy transfer (FRET) kinetic studies, we have investigated the search and bind process in the GRP1 PH domain at the molecular scale. We simulated the two membrane binding states of the GRP1 PH domain in the PIP3 search process, before and after the GRP1 PH domain docks with the PIP3 lipid. Our results suggest that the background anionic phosphatidylserine lipids, which constitute around one-fifth of the membrane by composition, play a critical role in the initial stages of recruiting protein to the membrane surface through non-specific electrostatic interactions. Our data also reveal a previously unseen transient membrane association mechanism that is proposed to enable a two-dimensional "hopping" search of the membrane surface for the rare PIP3 target lipid. We further modeled the PIP3-bound membrane-protein system using the EPR membrane docking structure for the MD simulations, quantitatively validating the EPR membrane docking structure and augmenting our understanding of the binding interface with atomic-level detail. Several observations and hypotheses reached from our MD simulations are also supported by experimental kinetic studies.

Pregnancy outcomes in sickle cell disease: a retrospective cohort study from two tertiary centres in the UK

The objective of this retrospective cohort study from two tertiary centres in the UK was to describe the pregnancy outcomes of women with sickle cell disease (SCD) who booked at these centres between 2004 and 2008, and to compare this with historical data. The study population comprised 122 singleton pregnancies in women with SCD: homozygous sickle cell disease 64, sickle cell haemoglobin C disease 45, sickle b plus thalassaemia 11, sickle cell haemoglobin E disease 1 and sickle cell delta disease 1 from 2004 to 2008 managed in the joint haematology/obstetric antenatal clinics in two tertiary teaching hospitals. The main outcome measures were the frequency of sickle cell crises and obstetric complications. Age and gestation at booking were 18-43 years (mean 29.7) and 9-36 weeks gestation (mean 17.3), respectively. Complications of SCD occurred in 25% of pregnancies. Fifty-four percent of women had induction of labour and 39% were delivered by emergency caesarean section. Thirty-three percent had a postpartum haemorrhage. Nineteen percent of women delivered before 37 completed weeks. Birth weight below 2500 g occurred in 20% of singleton pregnancies. Three neonates developed transient complications related to maternal opiate exposure postnatally. Three intrauterine deaths occurred at 24, 29 and 34 weeks. Two of these had congenital defects, and the other severe intrauterine growth restriction. No maternal deaths occurred. Successful pregnancy outcomes can be achieved in SCD. There has been an improvement in fetal and maternal morbidity and mortality compared with historical data. Pregnancy in women with SCD remains high risk. Early access to antenatal care and to expertise in SCD is essential. A matched control population from the same time period and prospective data collection is needed to address confounders such as ethnicity and deprivation.

Ovarian sickling as a proposed mechanism for premature ovarian failure necessitating ovum donation

Iron overload in female patients with sickle cell disease (SCD) has been reported to result in gonadal dysfunction. To date there has been no report in the literature of ovarian sickling being a reason for gonadodysgenesis (premature ovarian failure [POF]) in women. This case report describes POF in a woman with SCD and suggests ovarian sickling as its cause. We propose that frequent episodes of intravascular sickling, vessel occlusion and infarction as well as tissue hypoxia associated with chronic anaemia could account for the ovarian dysgenesis and hence POF.

Design, synthesis, and evaluation of biotinylated opioid derivatives as novel probes to study opioid pharmacology

A generally applicable strategy of chemically labeling (-)-morphine (1) is described. The synthesis starts from commercially available starting materials and can be completed in two steps with an overall yield of 23%. In silico simulation and NMR results show that the binding of (-)-morphine to one of its molecular targets, toll-like receptor 4 (TLR4), was not affected by the modification. Secreted embryonic alkaline phosphatase (SEAP) reporter assay results demonstrate that C(3) biotinylated and unmodified (-)-morphine show similar biological activities in live cells. To our knowledge, these studies provide the first practical and concise method to label various opioid derivatives, a group of important therapeutics in pain management, for biochemical/pharmacological studies.

Reliable operant apparatus for fish: audio stimulus generator, response button, and pellet-dispensing nipple

As part of ongoing research into the ability of koi to categorize complex auditory stimuli, we have had to develop novel apparatus. The stimulus generator presents sound from two CD drives under computer control through a new underwater speaker. The operant manipulandum is a horizontal button that eliminates spurious triggering by water turbulence and problematic response topographies. The button's design has also been adapted for use by tilapia in an aquacultural food-preference study. The feeder uses a nipple to dispense food pellets reliably under water. In this paper, the apparatus is described in detail. Also discussed are methodological issues related to its design, as well as its usage in a pilot study in which koi learned to discriminate music from silence by using a single manipulandum with food reinforcement.

Heterogeneity of Xanthomonas campestris pv. hederae Strains from Araliaceous Hosts

ABSTRACT Xanthomonas campestris pv. hederae (synonym X. hortorum pv. hederae) strains (59 total) were collected from plants in the araliaceae family. Strains were isolated from Hedera helix, Schefflera arboricola, Brassaia actinophylla, and Polyscias spp. from Florida, California, Hawaii, and New Zealand. All strains produced yellow mucoid growth; hydrolyzed esculin, starch, casein and gelatin; were pectolytic; produced urease; and grew on minimal media containing asparagine. All bacterial strains were pathogenic on H. helix (English ivy), B. actinophylla (dwarf schefflera), and Polyscias fruticosa (ming aralia). No differences in symptomatology were detected among strains; however, severity of symptoms usually was greatest on the host of origin. In planta growth rates of representative strains isolated from H. helix, B. actinophylla, and Polyscias spp. also were compared among these three hosts. In all cases, populations grew more rapidly when strains were inoculated to their original host species. All 59 bacterial strains were compared by 95-carbon source GN microplate, fatty acid methyl ester (FAME), and restriction fragment-length polymorphisms (RFLP), with the pulse-field gel electrophoresis method, analyses. All three analyses grouped strains into two distinct groups that correlated with the host of origin. Using metabolic profiles, 75% of the H. helix strains were separated from strains isolated from Brassaia and Schefflera and 95% of the Polyscias strains. FAME analysis separated strains into two distinct groups, with 96% of the H. helix strains placed in one group. RFLP analysis placed all of the H. helix and Schefflera strains in one group, as well as 33% of the Brassaia strains, whereas the other group contained all of the Polyscias strains and the remainder of the Brassaia strains. It is apparent that the pathovar hederae is made up of heterogeneous populations that can be separated by biochemical, pathological, genetic, and physiological analyses into two groups that are closely associated with the host of origin.

beta-adrenergic receptor sensitivity in cultured vascular smooth muscle cells: effect of age and of dietary restriction

The effect of age and of dietary restriction on vascular beta-receptor sensitivity was investigated using cultured smooth muscle cells from rat aortas. The growth rate was slower in cells obtained from 36-month-old rats than in cells obtained from 24-month-old rats and the cells from older animals achieved lower densities. The dietary restriction did not affect growth of cells from 24-month-old rats but increased cell numbers in 36-month-old rats. The elevation of the cyclic AMP level in response to epinephrine was decreased with age. Cells from dietary restricted animals responded more to epinephrine than cells from animals of the same age fed ad libitum.

Quantitation of cannabinoids in biological fluids by radioimmunoassay

A tritium based radioimmunoassay for delta9THC and its metabolites has been developed for the use of investigators studying the epidemiological, medical, clinical, and research aspects of cannabis use. The assay is sufficiently sensitive to detect cannabinoids in the urine of marijuana smokers for several days after their last exposure to the drug. The results obtained from a 28 day study indicate that the assay reflects the administration and removal of oral doses of THC. The specificity of the antisera, as determined in cross reactivity studies, allows not only the assay of metabolites in biological samples without interference from other drugs, but also the evaluation of extracts of other kinds of samples which may contain unmetabolized delta9THC. The technique of radioimmunoassay has many advantages over other methods of analysis. It is simple to perform and can be readily applied to the rapid analysis of large numbers of samples. It can be used in the direct analysis of physiological fluids and other biological samples which ordinarily have to be processed before other techniques can be applied. The method is non-destructive abd obviates the need to use radiolabelled drugs in man during metabolic and other studies. This radioimmunoassay has been designed with particular emphasis on ease of use by other investigators. We anticipate that it will prove useful to investigators and scientists for determining the absence, or presence and amount, of THC metabolite in a biological specimen, for epidemiologists in determining the full extent of cannabis use and to the medical/clinical community for establishing the minimum effective dose of delta9THC for each patient. The widespread application of a single method of analysis should also remove a great deal of the controversy surrounding marijuana studies performed to date.