MIND-DEPENDENT CONFORMATIONAL CHANGES IN MINE REGULATE THE MIN OSCILLATION

The min system comprised of MinC, MinD, and MinE in Escherichia coli ensures that cell division occurs at the midcell position by preventing the assembly of FtsZ into a Z-ring at the poles. MinD is a member of the deviant walker A motif family that dimerizes on the membrane in an ATP-dependent fashion. MinC forms an inhibitory complex with MinD on the membrane to antagonize Z-ring formation. MinE functions as a spatial regulator that displaces MinC from MinD and activates MinD ATPase. The dynamic interplay of the Min proteins culminates in a pole to pole oscillation by which a time-averaged MinCD concentration is the lowest at mid cell, thus allowing Z ring assembly there. MinD is at the heart of the Min system since MinD-ATP on the membrane recruits both MinC and MinE. In this study, MinD-D40A d10, an ATP hydrolysis-deficient MinD truncated for the C-terminal amphipathic helix involved in membrane binding, was crystallized in the presence of ATP. The structure resolved at 2.4Å resolution showed that MinD-ATP is a dimer. Furthermore, our mutagenesis studies demonstrate that the MinC and MinE binding sites form upon MinD dimerization and that MinE has a higher affinity for MinD than MinC. Prior to this study, E.coli MinE was thought to consist of two functionally autonomous domains. The N-terminal domain called anti-MinCD (MinE-CD) that suppresses MinCD activity is a nascent alpha helix. The C-terminal domain, known as the topological specificity domain (MinE-TSD) required for cell division at midcell, exists as a 4 beta stranded structure. However, recently determined structures of H. pylori and Neisseria gonorrhoeae MinE revealed that MinE exists as a 6 beta stranded form and part of MinE-CD is sequestered at the dimeric interface as a beta strand, thus raising question on how MinE interacts with MinD. We isolated MinE suppressor mutants that overcome some MinD mutants. These MinE mutants have substitutions at I24 position. Through a series of genetic and biochemical approaches we demonstrated that these substitutions for I24 release the sequestered part of MinE-CD, thereby converting the 6 beta to a 4 beta structure. The structures of MinD-D40A d10-MinE I24N and MinD-D40A d10-MinE peptide12-31, resolved at 4.2Å and 2.6Å resolution respectively, verified that MinE releases the beta strand upon MinD binding which is stabilized as an alpha helix at the MinD dimeric interface. In addition, we show that the N-terminal region of MinE-CD is a membrane targeting sequence (MTS) that is released during MinD-induced conformational alteration of MinE. Finally, we propose the Tarzan of the jungle model to explain how MinE can sequentially interact with multiple MinDs. MinE binding to MinD-ATP on the membrane triggers MinD ATPase activation, however, the mechanistic basis of the activation is still elusive. To get a sense of how MinE induces ATP hydrolysis in MinD, we compared the structure of MinD-D40A d10 with MinD-D40A d10 complexed with MinE12-31 peptide. Our analysis shows that MinE binding to MinD causes alterations in switch regions and conformational changes in some residues constituting MinDE binding interface. The MinD ATPase activation by MinE requires the binding of MinE-CD to the dimeric interface of a MinD dimer. Nonetheless, it was unknown whether MinE-CD binding to one side of the two dimeric interfaces is sufficient to stimulate MinD ATPase. To test this possibility, we created a MinD heterodimer composed of wild type MinD and a mutant form of MinD deficient in MinE binding. Our results show that both ATP molecules bound to a MinD heterodimer are hydrolyzed, suggesting that MinE-CD binding to one side of a MinD dimer induces ATP hydrolysis in both MinD subunits. Moreover, ATP hydrolysis was also observed in a heterodimer of the hydrolytic-deficient MinD-D40A mutant and the MinD mutant deficient in MinE binding. Taken together, we propose an asymmetric activation model where MinD hydrolyzes ATP upon MinE-CD binding to one side of the MinD dimer

Photothermal Polymer Nanocomposites of Tungsten Bronze Nanorods with Enhanced Tensile Elongation at Low Filler Contents

We present polymer nanocomposites of tungsten bronze nanorods (TBNRs) and ethylene propylene diene monomers (EPDM). The combination of these components allows the simultaneous enhancement in the mechanical and photothermal properties of the composites at low filler contents. The as-synthesized TBNRs had lengths and diameters of 14.0 +/- 2.4 nm and 2.5 +/- 0.5 nm, respectively, and were capped with oleylamine, which has a chemical structure similar to EPDM, making the TBNRs compatible with the bulk EPDM matrix. The TBNRs absorb a wide range of near-infrared light because of the sub-band transitions induced by alkali metal doping. Thus, the nanocomposites of TBNRs in EPDM showed enhanced photothermal properties owing to the light absorption and subsequent heat emission by the TBNRs. Noticeably, the nanocomposite with only 3 wt% TBNRs presented significantly enhanced tensile strain at break, in comparison with those of pristine EPDM, nanocomposites with 1 and 2 wt % TBNRs, and those with tungsten bronze nanoparticles, because of the alignment of the nanorods during tensile elongation. The photothermal and mechanical properties of these nanocomposites make them promising materials for various applications such as in fibers, foams, clothes with cold weather resistance, patches or mask-like films for efficient transdermal delivery upon heat generation, and photoresponsive surfaces for droplet transport by the thermocapillary effect in microfluidic devices and microengines

Metal-organic frameworks constructed from flexible ditopic ligands: Conformational diversity of an aliphatic ligand

The solvothermal reaction of adipic acid as a flexible ditopic ligand and the metal ions MnII, CoII, and TbIII afforded three novel metal-organic frameworks (MOFs), {[Mn2(adipate) 2(DMA)]} (1), {[Co2(adipate)2(DMF)] ??1DMF??1.5H2O} (2), and {[Tb3(adipate) 4.5(DMF)2]} (3) (DMA = N,N-dimethylacetamide; DMF = N,N-dimethylformamide), respectively, which were structurally characterized by single-crystal X-ray diffraction. Depending on the kind of metal ion and solvent system, the conformations and coordination modes of the adipate ligands were diverse and governed the entire MOF structure. Compound 1 consists of the secondary building units (SBUs) of Mn-O chains that were linked by adipate ligands extending in two-dimensional sheets, which were infinitely stacked in a layer-by-layer manner. Compound 2 presented a three-dimensional MOF constructed from Co-O chains and bridging adipate ligands extending in four different directions. Compound 3 also had a three-dimensional structure which was formed by Tb-O chains connected with adipate ligands in six directions. From these structures, ten different adipate ligands with diverse conformations were found, and the potential energy of each conformation was calculated by the first-principles density function. In addition, the luminescence properties of the Tb-based MOF 3 were investigated in the solid state at room temperature.close0

Global Imbalances: Time for Action

The world economy faces a grave danger from the large imbalances in current account positions. Policymakers should not wait until financial markets force global adjustment. They should initiate a credible, comprehensive adjustment program to reduce the risks of a crisis, which could produce a world recession and disruptions to the global trading system. Participants in a February 2007 workshop, held in Washington and sponsored by Brussels-based Bruegel, Seoul-based Korea Institute for International Economic Policy, and Washington-based Peterson Institute for International Economics, outlined how an orderly reduction in global imbalances can be achieved. They presented estimates of the exchange rate implications of current account adjustment scenarios in which the US current account deficit narrowed to 3 percent of GDP in the medium term and the world growth rate was unchanged. Most of the adjustment would be borne by China, Japan, other Asian economies, a few high-surplus European economies not in the euro area, and the oil-exporting countries. The combined role of the smaller surplus economies in Asia and Europe (outside of the euro area) in the adjustment process will be more important than the role of either China or Japan. The adjustment would require a rebalancing of world demand with both higher saving in the United States and higher consumption in East Asia, as well as effective appreciations of the currencies of China, Japan, and other surplus countries in East Asia and Europe and bilateral appreciations against the dollar by other currencies. The problem is multilateral in nature and needs to be addressed in a multilateral context such as that potentially provided by the International Monetary Fund.

Schwannoma Mimicking Laryngocele

A schwannoma of the larynx is a rare benign tumor that usually presents as a submucosal mass in the pyriform sinus and the aryepiglottic space, and this type of schwannoma constitutes a diagnostic and therapeutic challenge for otolaryngologists. We present here two cases of supraglottic schwannomas that were misdiagnosed as laryngoceles. Both were excised through a lateral thyrotomy approach without a tracheostomy, and the laryngeal function was successfully maintained. We discuss the clinical and imaging findings and the management of this rare neoplasm with focusing on the differential diagnosis of laryngeal schwannoma and laryngocele. We also review the relevant medical literature

Association between polymorphisms of arachidonate 12-lipoxygenase (ALOX12) and schizophrenia in a Korean population

Arachidonic acid (AA), an essential polyunsaturated fatty acid, is one of the major components of neural membranes, which show an altered phospholipid composition in schizophrenia. Arachidonate 12-lipoxygenase (ALOX12), an important enzyme, metabolizes AA to 12-HPETE, which affects catecholamine synthesis. However, research has yet to show the genetic association between ALOX12 and schizophrenia. Therefore, we investigated single nucleotide polymorphisms (SNP) of the ALOX12 gene in schizophrenia, recruiting patients with schizophrenia (n = 289) and normal controls (n = 306) from a Korean population. We selected three SNPs (rs1126667, rs434473, and rs1042357) of the ALOX12 gene and genotyped them by direct sequencing. We reviewed the schizophrenic patients' medical records and assessed them clinically using the Brief Psychiatric Rating Scale (BPRS), the Scale for the Assessment of Negative Symptoms (SANS), and the Operational Criteria Checklist (OPCRIT). Then we statistically analyzed the genetic associations between the SNPs and schizophrenia, finding a genetic association between both rs1126667 and rs1042357 and schizophrenia, in the recessive model (p = 0.015 and 0.015, respectively). We also found an association between rs434473 and negative symptoms, defined through a factor analysis of the OPCRIT data (p = 0.040). Consequently, we suggest that SNPs of the ALOX12 gene might be associated with schizophrenia and negative symptoms in this Korean population. These weak positives require additional study

Global imbalances: time for action

Increasing nervousness in world financial markets give new relevance to the long-standing issues of global current account adjustment. It reminds policymakers that this adjustment, if improperly managed, could lead to further drops in assets prices, disruptions in the global trading system, and possible world recession. The authors of this Policy Brief assess how to achieve an orderly reduction in the large and unsustainable global current account imbalances. The Policy Brief is the result of a joint conference held in Washington, D.C. on February 8 and 9 2007.