Membrane transporters that use energy stored in sodium gradients to drive nutrients into cells constitute a major class of proteins. We report the crystal structure of a member of the solute sodium symporters (SSS), the Vibrio parahaemolyticus sodium/galactose symporter (vSGLT). The ~3.0Å structure contains 14 transmembrane helices in an inward facing conformation with a core structure of inverted repeats of 5 TM helices (TM2-TM6 and TM7-TM11). Galactose is bound in the center of the core, occluded from the outside solutions by hydrophobic residues. Surprisingly, the architecture of the core is similar to the leucine transporter (LeuT) from a different gene family. Modeling the outward-facing conformation based on the LeuT structure, in conjunction with biophysical data, provides insight into structural rearrangements for active transport.

Membrane co-transport proteins that utilize a 5-helix inverted repeat motif have recently emerged as one of the largest structural class of secondary active transporters1,2. However, despite many structural advances there is no clear evidence as to how ion and substrate transport are coupled. Here, we report a comprehensive study of the Sodium-Galactose Transporter from Vibrio parahaemolyticus (vSGLT) consisting of molecular dynamics simulations, biochemical characterization, and a new crystal structure of the inward-open conformation at 2.7 Å resolution. Our data show that sodium exit causes a reorientation of transmembrane helix 1 (TM1) opening an inner gate required for substrate exit, while also triggering minor rigid body movements in two sets of transmembrane helical bundles. This cascade of events, initiated by sodium release, ensures proper timing of ion and substrate release. Once set in motion, these molecular changes weaken substrate binding to the transporter and allow galactose to readily enter the intracellular space. Additionally, we identify an allosteric pathway between the sodium binding sites, the unwound portion of TM1, and the substrate binding site that is essential in the coupling of co-transport.

The objective of this paper is to offer experimental evidence which shows that the process of excitation in the nerve is accompanied by a transient change in optical properties of the nervous tissue. The optical properties examined include fluorescence, turbidity, and birefringence.Changes in fluorescence were examined after nervous tissues were stained with the dye 8-anilinonaphthalene-1-sulfonic acid (ANS).1 Our search for fluorescence under these conditions was prompted by the work of Aronson, Detert, and Morales,2 who demonstrated that the fluorescence of ANS is extremely sensitive to conformational changes of various macromolecules.Our attempt to measure turbidity changes of the nerve during excitation was made with a view to extending the work reported by Cohen and Keynes3 by the use of monochromatic light.The observation by Inoue and Sato4 of rapid changes in the mitotic figure of the Pectinaria obcyte under a polarizing microscope aroused our interest in the birefringent properties of the nerve during excitation. Our experiments along this line were greatly accelerated when we encountered a very significant paper by Cohen et al.5 on this subject in the early stages of our investigation.Changes in the optical properties of the nerve during excitation are very small. In fluorescence and turbidity studies, optical signs of nerve excitation could not be measured without the use of a computer to average multiple responses. However, in birefringence studies, it was possible to record optical signs of nerve excitation directly on an oscillograph screen.

Novel APOBEC1 target 1 (Nat1) (also known as "p97," "Dap5," and "Eif4g2") is a ubiquitously expressed cytoplasmic protein that is homologous to the C-terminal two thirds of eukaryotic translation initiation factor 4G (Eif4g1). We previously showed that Nat1-null mouse embryonic stem cells (mES cells) are resistant to differentiation. In the current study, we found that NAT1 and eIF4G1 share many binding proteins, such as the eukaryotic translation initiation factors eIF3 and eIF4A and ribosomal proteins. However, NAT1 did not bind to eIF4E or poly(A)-binding proteins, which are critical for cap-dependent translation initiation. In contrast, compared with eIF4G1, NAT1 preferentially interacted with eIF2, fragile X mental retardation proteins (FMR), and related proteins and especially with members of the proline-rich and coiled-coilcontaining protein 2 (PRRC2) family. We also found that Nat1-null mES cells possess a transcriptional profile similar, although not identical, to the ground state, which is established in wild-type mES cells when treated with inhibitors of the ERK and glycogen synthase kinase 3 (GSK3) signaling pathways. In Nat1-null mES cells, the ERK pathway is suppressed even without inhibitors. Ribosome profiling revealed that translation of mitogen-activated protein kinase kinase kinase 3 (Map3k3) and son of sevenless homolog 1 (Sos1) is suppressed in the absence of Nat1. Forced expression of Map3k3 induced differentiation of Nat1-null mES cells. These data collectively show that Nat1 is involved in the translation of proteins that are required for cell differentiation.Nat1 | Eif4g1 | translation control | Map3k3 | mouse embryonic stem cells

Transmission across the septal junctions of the segmented giant axons of crayfish is accounted for quantitatively by a simple equivalent circuit. The septal membranes are passive, resistive components and transmission is ephaptic, by the electrotonic spread of the action current of the pre-septal spike. The electrotonic spread appears as a septal potential, considerably smaller than the pre-septal spike, but usually still large enough to initiate a new spike in the post-septal segments. The septal membranes do not exhibit rectification, at least over a range of 4-25 mv polarization and this accounts for their capacity for bidirectional transmission. The commissural branches, which are put forth by each lateral axon, make functional connections between the two axons. Transmission across these junctions can also be bidirectional and is probably also ephaptic. Under various conditions, the ladder-like network of crossconnections formed by the commissural junctions can give rise to circus propagation of impulses from one axon to the other. This can give rise to reverberatory activity of both axons at frequencies as high as 400/sec. I N T R O D U C T I O NT h e discovery of segmented septate giant axons in crayfish (55) and earthw o r m (76) raised a new type of p r o b l e m regarding the n a t u r e of transmissional processes. Like other giant axons of invertebrates (cf. reference 86) the septate nerves arise by fusion of small fibers of m a n y ceils. In the septate axons, however, the fused process originates from a segmental group of cells and the fiber p r o d u c e d in each segment abuts its neighbors in the segments fore and aft. A l t h o u g h in some forms the axons of several segments m a y fuse, in crayfish the axons of the individual segments are separated by m e m b r a n e s or septa. T h e m e m b r a n e s have been studied with the electron microscope recently by H a m a (48). Unlike the septal surfaces of earthworms (47, but of. 45 • I 9 6 r tissue. They form a layer about 2 ~ thick in the crayfish. There are occasional patches or "windows," however, where the two axonal membranes come together to lie only about 100 A apart. It was inferred (55, 76) that the segmented giant axons, which run the length of the animal, were through conducting systems of considerable importance to nervous functioning. The septa appeared to be so different in structure from synapses that Johnson (55) thought they also represented a different mode of transmissional activity. Stough (76) and Holmes (53), however, held that the septal membranes formed synaptic structures.Electrophysiological data demonstrated that the segmented axons conducted impulses in both directions in earthworm (14,24,74) and in crayfish (85). These findings emphasized the difference between the bidirectional septa and unidirectional synapses, and the former were termed "unpolarized synapses" (cf. reference 15). Wiersma (85) noted that transmissional delay at the septa was brief, whereas a significant delay ranging up to several millisec...

BACKGROUND AND PURPOSE:Spontaneous intracranial hypotension (SIH) presents with orthostatic headache, and the diagnosis is made on the basis of low CSF pressure and brain MR imaging findings characteristic of the disorder. However, a broad spectrum of symptoms and MR imaging findings of SIH is recognized, and some cases have no typical MR imaging abnormalities. SIH is believed to be caused by CSF leakage from the spinal dural sac, whereas the usefulness of MR imaging of the spine remains unclear. Our aim was to elucidate the diagnostic value of brain and spinal MR imaging

Lysophosphatidylcholine (lysoPC) evokes diverse biological responses in vascular cells including Ca(2+) mobilization, production of reactive oxygen species, and activation of the mitogen-activated protein kinases, but the mechanisms linking these events remain unclear. Here, we provide evidence that the response of mitochondria to the lysoPC-dependent increase in cytosolic Ca(2+) leads to activation of the extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase through a redox signaling mechanism in human umbilical vein endothelial cells. ERK activation was attenuated by inhibitors of the electron transport chain proton pumps (rotenone and antimycin A) and an uncoupler (carbonyl cyanide p-trifluoromethoxyphenylhydrazone), suggesting that mitochondrial inner membrane potential plays a key role in the signaling pathway. ERK activation was also selectively attenuated by chain-breaking antioxidants and by vitamin E targeted to mitochondria, suggesting that transduction of the mitochondrial hydrogen peroxide signal is mediated by a lipid peroxidation product. Inhibition of ERK activation with MEK inhibitors (PD98059 or U0126) diminished induction of the antioxidant enzyme heme oxygenase-1. Taken together, these data suggest a role for mitochondrially generated reactive oxygen species and Ca(2+) in the redox cell signaling path-ways, leading to ERK activation and adaptation of the pathological stress mediated by oxidized lipids such as lysoPC.

The dimensions of the 10 triangles around the cavernous sinus were measured to define the anatomical characteristics of the triangles and to compare their consistency in shape and area. Twelve tissue blocks containing the bilateral cavernous sinuses and medial two-thirds of the middle cranial fossae were obtained from Japanese adults at autopsy, fixed to a stereotactic frame, and examined with an operative microscope. The dimensions of each triangle were measured with calipers and compared, based on the same point and border. The anteromedial triangle and the superolateral (Parkinson's) triangle were more consistent in shape than the paramedial and oculomotor triangles, but the oculomotor triangle was larger in area than these other triangles. The posteromedial (Kawase's) triangle was more consistent in shape and larger than the anterolateral, lateral, and the posterolateral (Glasscock's) triangles. The anteromedial and superolateral (Parkinson's) triangles are important for the combined epi- and subdural approach to cavernous sinus lesions. The posteromedial (Kawase's) triangle is important for gaining access to the posterior cranial fossa from the middle cranial fossa.