17 research outputs found
An NLR paralog Pit2 generated from tandem duplication of Pit1 fine-tunes Pit1 localization and function
NLR family proteins act as intracellular receptors. Gene duplication amplifies the number of NLR genes, and subsequent mutations occasionally provide modifications to the second gene that benefits immunity. However, evolutionary processes after gene duplication and functional relationships between duplicated NLRs remain largely unclear. Here, we report that the rice NLR protein Pit1 is associated with its paralogue Pit2. The two are required for the resistance to rice blast fungus but have different functions: Pit1 induces cell death, while Pit2 competitively suppresses Pit1-mediated cell death. During evolution, the suppression of Pit1 by Pit2 was probably generated through positive selection on two fate-determining residues in the NB-ARC domain of Pit2, which account for functional differences between Pit1 and Pit2. Consequently, Pit2 lost its plasma membrane localization but acquired a new function to interfere with Pit1 in the cytosol. These findings illuminate the evolutionary trajectory of tandemly duplicated NLR genes after gene duplication
Dynamic Regulation of Myosin Light Chain Phosphorylation by Rho-kinase
Myosin light chain (MLC) phosphorylation plays important roles in various cellular functions such as cellular morphogenesis, motility, and smooth muscle contraction. MLC phosphorylation is determined by the balance between activities of Rho-associated kinase (Rho-kinase) and myosin phosphatase. An impaired balance between Rho-kinase and myosin phosphatase activities induces the abnormal sustained phosphorylation of MLC, which contributes to the pathogenesis of certain vascular diseases, such as vasospasm and hypertension. However, the dynamic principle of the system underlying the regulation of MLC phosphorylation remains to be clarified. Here, to elucidate this dynamic principle whereby Rho-kinase regulates MLC phosphorylation, we developed a mathematical model based on the behavior of thrombin-dependent MLC phosphorylation, which is regulated by the Rho-kinase signaling network. Through analyzing our mathematical model, we predict that MLC phosphorylation and myosin phosphatase activity exhibit bistability, and that a novel signaling pathway leading to the auto-activation of myosin phosphatase is required for the regulatory system of MLC phosphorylation. In addition, on the basis of experimental data, we propose that the auto-activation pathway of myosin phosphatase occurs in vivo. These results indicate that bistability of myosin phosphatase activity is responsible for the bistability of MLC phosphorylation, and the sustained phosphorylation of MLC is attributed to this feature of bistability
Liliequist Membrane: Three-dimensional Constructive Interference in Steady State MR Imaging
PURPOSE: To evaluate the Liliequist membrane in healthy volunteers by using three-dimensional (3D) Fourier transformation constructive interference in steady state (CISS) magnetic resonance (MR) imaging. MATERIALS AND METHODS: In 31 volunteers, the authors performed 3D CISS MR imaging. They divided the membrane into three segments: the sellar, diencephalic, and mesencephalic segments. MR images were evaluated to identify the segments, superior and inferior attachments, lateral border, and thickness of the Liliequist membrane. RESULTS: Three-dimensional CISS MR imaging depicted the sellar, diencephalic, and mesencephalic segments of the Liliequist membrane in the sagittal plane in 25 (81%), 16 (52%), and five (16%) of the 31 subjects, respectively. Transverse MR imaging depicted these segments in 24 (77%), 10 (32%), and two (6%) subjects, respectively, and coronal MR imaging depicted them in 24 (77%), 12 (39%), and two (6%) subjects, respectively. Clear attachment of the membrane to the dorsum sellae was observed in 22 (88%) of 25 subjects in whom the sellar segment was identified. Clear attachment to the mamillary body was identified in eight (50%) of 16 subjects in whom the diencephalic segment was identified. The Liliequist membrane was attached to the oculomotor nerve on seven (14%) of 50 sides of the lateral border and to the arachnoid membrane around the oculomotor nerve on 28 (56%) sides. In the sagittal plane, the thickness of the membrane was less than one-half the thickness of the third ventricle floor in 22 (88%) of 25 subjects. CONCLUSION: The Liliequist membrane can be visualized by using 3D CISS MR sequences
The Evolution of Intermolecular Energy Bands of Occupied and Unoccupied Molecular States in Organic Thin Films
In
organic semiconductors, the hole and electron transport occurs
through the intermolecular overlaps of highest occupied molecular
orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO), respectively.
A measure of such intermolecular electronic coupling is the transfer
integral, which can experimentally be observed as energy level splittings
or the width of the respective energy bands. Quantum chemistry textbooks
describe how an energy level splits into two levels in molecular dimers,
into three levels in trimers and evolves into an energy band in infinite
systems, a process that has never been observed for the LUMO or beyond
dimers for the HOMO. In this work, our new technique, low-energy inverse
photoelectron spectroscopy, was applied to observe the subtle change
of the spectral line shape of a LUMO-derived feature while we used
ultraviolet photoelectron spectroscopy to investigate the occupied
states. We show at first that tin-phthalocyanine molecules grow layer-by-layer
in quasi-one-dimensional stacks on graphite, and then discuss a characteristic
and systematic broadening of the spectral line shapes of both HOMO
and LUMO. The results are interpreted as energy-level splittings due
to the intermolecular electronic couplings. On the basis of the Hückel
approximation, we determined the transfer integrals for HOMO–1,
HOMO, and LUMO to be ≤15 meV, (100 ± 10) meV, and (128
± 10) meV, respectively
The Complex Polymorphism and Thermodynamic Behavior of a Seemingly Simple System: Naphthalene on Cu(111)
Naphthalene,
C<sub>10</sub>H<sub>8</sub>, is a polycyclic aromatic
hydrocarbon (PAH) consisting of two fused benzene rings. From previous
studies, it is known to form three different commensurate structures
in thin epitaxial films on Cu(111), depending on the preparation conditions.
One of these structures even exhibits a chiral motif of molecular
rotations within the unit cell. In an attempt to elucidate this polymorphism,
we performed in situ low-energy electron diffraction (LEED) as a function
of temperature and surface coverage, revealing an unexpected and extraordinarily
complex structural and thermodynamic behavior. We present experimental
evidence for a phase transition from a two-dimensional gas to a highly
ordered molecular solid via an intermediate metastable phase with
moderate order (extending over a few lattice constants only) which
undergoes a reversible orientational shift upon temperature variation.
At monolayer coverage and above, we find that two different point-on-line
(POL) coincident epitaxial relations constitute the dominant structures.
This is remarkable because, so far, POL structures of naphthalene
on Cu(111) and other substrates have either not been recognized or
not obtained under the respective experimental conditions. Our results
are corroborated by the analysis of characteristic moiré patterns
observed in scanning tunneling microscopy (STM), indicative of a noncommensurate
epitaxial registry
Decay of the Exciton in Quaterthiophene-Terminated Alkanethiolate Self-Assembled Monolayers on Au(111)
The dynamics of the
photoexcited states in the quaterthiophene-terminated
alkanethiolate self-assembled monolayer (SAM) on Au(111) are investigated
using time-resolved two-photon photoemission (2PPE) spectroscopy.
For SAMs with various alkylene (−(CH<sub>2</sub>)<sub><i>n</i></sub>−) chain lengths, a common stand-up configuration
of the quaterthiophene (4T) group is confirmed by infrared reflection
absorption spectroscopy (IRAS); the −(CH<sub>2</sub>)<sub><i>n</i></sub>– length controls the distance between 4T
and Au. Although the binding energies of the occupied and unoccupied
electronic levels of the 4T moiety are similar for all SAMs, the decay
dynamics of the photoexcited electrons at 4T strongly depends on the
−(CH<sub>2</sub>)<sub><i>n</i></sub>– length;
the lifetime changes from 0.2 to 3.9 ps by changing <i>n</i> from 3 to 13. The <i>n</i> dependent decay is explained
by the excitation transfer from 4T to the Au substrate