Multiple environmental changes induce interactive effects on bacterial degradation activity in the Arctic Ocean

The Arctic Ocean faces multiple environmental changes induced by climate change on both global and regional scale. In addition to global changes in seawater temperature and pH, Arctic waters receive organic matter enrichment due to increasing pelagic primary production, enhanced sea ice melting and increasing terrestrial carbon loads. We experimentally tested individual and combined effects of warming, acidification and organic matter amendment on growth, biomass production and extracellular enzyme activities of bacterioplankton in Fram Strait during early summer. Results reveal pH optima of 6.7–7.6 for extracellular leucine-aminopeptidase and below pH 6.0 for beta-glucosidase in the West Spitsbergen Current. These optima well below the current seawater pH imply increasing hydrolytic activity with ongoing ocean acidification. However, the new synthesis of extracellular enzymes during 4-d incubations obscured the biochemical pH effects. Elevated temperature and carbohydrate supply had strongly interactive effects on bacterial biomass production in both Atlantic Water of the West Spitsbergen Current and Polar Water of the East Greenland Current. Activation energies ranged from 45 kJ mol−1 to 52 kJ mol−1 at in situ substrate concentration, while substantially higher values of 122–174 kJ mol−1 could be estimated from incubations with carbohydrate addition. The net loss of total amino acids in carbohydrate-amended incubations was significantly reduced at elevated temperature in all experiments, suggesting enhanced de novo synthesis. Our findings show that the complexity of combined effects must be considered to better assess the potential of climate change to alter biogenic carbon and energy fluxes in marine systems

Regulation of dynamic polarity switching in bacteria by a Ras-like G-protein and its cognate GAP

The rod-shaped cells of the bacterium Myxococcus xanthus move uni-directionally and occasionally undergo reversals during which the leading/lagging polarity axis is inverted. Cellular reversals depend on pole-to-pole relocation of motility proteins that localize to the cell poles between reversals. We show that MglA is a Ras-like G-protein and acts as a nucleotide-dependent molecular switch to regulate motility and that MglB represents a novel GTPase-activating protein (GAP) family and is the cognate GAP of MglA. Between reversals, MglA/GTP is restricted to the leading and MglB to the lagging pole defining the leading/lagging polarity axis. For reversals, the Frz chemosensory system induces the relocation of MglA/GTP to the lagging pole causing an inversion of the leading/lagging polarity axis. MglA/GTP stimulates motility by establishing correct polarity of motility proteins between reversals and reversals by inducing their pole-to-pole relocation. Thus, the function of Ras-like G-proteins and their GAPs in regulating cell polarity is found not only in eukaryotes, but also conserved in bacteria

Epilepsy surgery in drug resistant temporal lobe epilepsy associated with neuronal antibodies

We assessed the outcome of patients with drug resistant epilepsy and neuronal antibodies who underwent epilepsy surgery. Retrospective study, information collected with a questionnaire sent to epilepsy surgery centers. Thirteen patients identified, with antibodies to GAD (8), Ma2 (2), Hu (1), LGI1 (1) or CASPR2 (1). Mean age at seizure onset: 23 years. Five patients had an encephalitic phase. Three had testicular tumors and five had autoimmune diseases. All had drug resistant temporal lobe epilepsy (median: 20 seizures/month). MRI showed unilateral temporal lobe abnormalities (mainly hippocampal sclerosis) in 9 patients, bilateral abnormalities in 3, and was normal in 1. Surgical procedures included anteromesial temporal lobectomy (10 patients), selective amygdalohippocampectomy (1), temporal pole resection (1) and radiofrequency ablation of mesial structures (1). Perivascular lymphocytic infiltrates were seen in 7/12 patients. One year outcome available in all patients, at 3 years in 9. At last visit 5/13 patients (38.5%) (with Ma2, Hu, LGI1, and 2 GAD antibodies) were in Engel's classes I or II. Epilepsy surgery may be an option for patients with drug resistant seizures associated with neuronal antibodies. Outcome seems to be worse than that expected in other etiologies, even in the presence of unilateral HS. Intracranial EEG may be required in some patients

Epilepsy, hippocampal sclerosis and febrile seizures linked by common genetic variation around SCN1A

Epilepsy comprises several syndromes, amongst the most common being mesial temporal lobe epilepsy with hippocampal sclerosis. Seizures in mesial temporal lobe epilepsy with hippocampal sclerosis are typically drug-resistant, and mesial temporal lobe epilepsy with hippocampal sclerosis is frequently associated with important co-morbidities, mandating the search for better understanding and treatment. The cause of mesial temporal lobe epilepsy with hippocampal sclerosis is unknown, but there is an association with childhood febrile seizures. Several rarer epilepsies featuring febrile seizures are caused by mutations in SCN1A, which encodes a brain-expressed sodium channel subunit targeted by many anti-epileptic drugs. We undertook a genome-wide association study in 1018 people with mesial temporal lobe epilepsy with hippocampal sclerosis and 7552 control subjects, with validation in an independent sample set comprising 959 people with mesial temporal lobe epilepsy with hippocampal sclerosis and 3591 control subjects. To dissect out variants related to a history of febrile seizures, we tested cases with mesial temporal lobe epilepsy with hippocampal sclerosis with (overall n = 757) and without (overall n = 803) a history of febrile seizures. Meta-analysis revealed a genome-wide significant association for mesial temporal lobe epilepsy with hippocampal sclerosis with febrile seizures at the sodium channel gene cluster on chromosome 2q24.3 [rs7587026, within an intron of the SCN1A gene, P = 3.36 × 10−9, odds ratio (A) = 1.42, 95% confidence interval: 1.26-1.59]. In a cohort of 172 individuals with febrile seizures, who did not develop epilepsy during prospective follow-up to age 13 years, and 6456 controls, no association was found for rs7587026 and febrile seizures. These findings suggest SCN1A involvement in a common epilepsy syndrome, give new direction to biological understanding of mesial temporal lobe epilepsy with hippocampal sclerosis with febrile seizures, and open avenues for investigation of prognostic factors and possible prevention of epilepsy in some children with febrile seizure

Genome-wide identification and phenotypic characterization of seizure-associated copy number variations in 741,075 individuals

Copy number variants (CNV) are established risk factors for neurodevelopmental disorders with seizures or epilepsy. With the hypothesis that seizure disorders share genetic risk factors, we pooled CNV data from 10,590 individuals with seizure disorders, 16,109 individuals with clinically validated epilepsy, and 492,324 population controls and identified 25 genome-wide significant loci, 22 of which are novel for seizure disorders, such as deletions at 1p36.33, 1q44, 2p21-p16.3, 3q29, 8p23.3-p23.2, 9p24.3, 10q26.3, 15q11.2, 15q12-q13.1, 16p12.2, 17q21.31, duplications at 2q13, 9q34.3, 16p13.3, 17q12, 19p13.3, 20q13.33, and reciprocal CNVs at 16p11.2, and 22q11.21. Using genetic data from additional 248,751 individuals with 23 neuropsychiatric phenotypes, we explored the pleiotropy of these 25 loci. Finally, in a subset of individuals with epilepsy and detailed clinical data available, we performed phenome-wide association analyses between individual CNVs and clinical annotations categorized through the Human Phenotype Ontology (HPO). For six CNVs, we identified 19 significant associations with specific HPO terms and generated, for all CNVs, phenotype signatures across 17 clinical categories relevant for epileptologists. This is the most comprehensive investigation of CNVs in epilepsy and related seizure disorders, with potential implications for clinical practice

Painfully Energetic : A tale of two proteins potentially connected

NADH:quinone oxidoreductase (Complex I) is the first enzyme of the respiratory chain and is involved in energy conservation generating an electro-chemical gradient across a membrane. The enzyme can be divided into a membrane spanning domain and a hydrophilic domain, which protrudes from the membrane. In the hydrophilic domain electrons from NADH oxidation are transported via a wire of iron-sulfur (Fe-S ) clusters to quinone, which is reduced. While the membrane domain is responsible for proton translocation to maintain the proton motive force, which is important for ATP synthesis. Large protein complexes like complex I have evolved from an assembly of discrete functional building blocks of which there are extant homologs. Two very different protein families, the Mrpantiporter and membrane bound [NiFe]-hydrogenases contain subunits which are homologous to complex I subunits. Part one of this work aimed to better understand the functional relationship between the related protein subunits of complex I, Mrp-antiporter and [NiFe]-hydrogenases. This knowledge will help us to elucidate the proton translocation pathway in complex I. First we compared the functional differentiation of complex I antiporter-like subunits with transporter subunits of the Hyc and Hyf hydrogenases and the 11-subunit complex I. For that we tested if the different subunits could rescue the growth of two salt sensitive Bacillus subtilis strain, which each lacked one of the two large Mrp-antiporter subunits (MrpA/MrpD). The 11-subunit complex I subunits could restore the growth in a similar manner as the complex I subunits, whereas the hydrogenase subunits could substitute equally well for the two MrpA and MrpD. We confirmed that 11-subunit complex I is a bona fide complex I. and that the hydrogenase subunits have intermediate forms of the antiporter-like subunits. Secondly we examined the functional relationship of the two homologous proteins MrpA from the Mrp-antiporter and NuoL from complex I. We located a stretch of amino acid residues which is conserved only in NuoL and MrpA, but not in the other complex I antiporter-like subunits or in MrpD. These residues were subjected to site directed mutagenesis and any resulting effects were examined in vivo by B. subtilis complementation studies and 23Na-NMR. Only one mutation (M258I/M225I) showed differences in the efficiency of cell growth and sodium efflux in both subunits, the other mutants were all able to cope with high salt levels.Ion channels are important for many processes in the cell and critically depend on gradients over membranes to execute their functions. They are involved in the detection of changes in the environment, which is an important survival mechanism for every organism. One of these ion channels is TRPA1, which belongs to the TRP superfamily of non-selective cation channels. TRPA1 can be activated by changes in temperature and voltage, as well as by a wide range of electrophilic and non-electrophilic chemicals. As structural information is limited, the exact activation mechanism is still elusive. The aim of the second part was to study the structural and functional changes of TRPA1 upon activation by temperature and chemical activators. We studied the effect of increased temperature and ligands on the conformation of mosquito TRPA1 (AgTRPA1), using intrinsic tryptophan fluorescence, SRCD and nanoDSF. We showed that the electrophilic ligands tested were quenching the tryptophan flourescence in the same way, suggesting a similar binding mechanism. We propose a putative model how temperature and ligand can activate AgTRPA1.Furthermore, we truncated the C-terminal region of human TRPA1, in an attempt to narrow down the minimal structural and functional unit of hTRPA1. This will facilitate future structural and functional studies of the activation mechanism

Functional differentiation of antiporter-like polypeptides in complex I; a site-directed mutagenesis study of residues conserved in MrpA and NuoL but Not in MrpD, NuoM, and NuoN

It has long been known that the three largest subunits in the membrane domain (NuoL, NuoM and NuoN) of complex I are homologous to each other, as well as to two subunits (MrpA and MrpD) from a Na+ /H+ antiporter, Mrp. MrpA and NuoL are more similar to each other and the same is true for MrpD and NuoN. This suggests a functional differentiation which was proven experimentally in a deletion strain model system, where NuoL could restore the loss of MrpA, but not that of MrpD and vice versa. The simplest explanation for these observations was that the MrpA and MrpD proteins are not antiporters, but rather single subunit ion channels that together form an antiporter. In this work our focus was on a set of amino acid residues in helix VIII, which are only conserved in NuoL and MrpA (but not in any of the other antiporter-like subunits.) and to compare their effect on the function of these two proteins. By combining complementation studies in B. subtilis and 23Na-NMR, response of mutants to high sodium levels were tested. All of the mutants were able to cope with high salt levels; however, all but one mutation (M258I/M225I) showed differences in the efficiency of cell growth and sodium efflux. Our findings showed that, although very similar in sequence, NuoL and MrpA seem to differ on the functional level. Nonetheless the studied mutations gave rise to interesting phenotypes which are of interest in complex I research