A novel concept of a light-emitting diode (LED) is proposed and demonstrated in which the active region of the device is placed in a resonant optical cavity. As a consequence, the optical emission from the active region is restricted to the modes of the cavity. Resonant cavity light-emitting diodes (RCLED) have higher spectral purity and higher emission intensity as compared to conventional light emitting diodes. Results on a top-emitting RCLED structure with AlAs/Al,Gai _ As quarter wave mirrors grown by molecular beam epitaxy are presented. The experimental emission linewidth is 17 meV (0.65 kT) at room temperature. The top-emission intensity is a factor of 1.7 higher as compared to conventional LEDs.

Using a combination of protease protection, glycosylation, and carbonate extraction assays, we have characterized the topogenic determinants encoded by Kv1.3 segments that mediate translocation events during endoplasmic reticulum (ER) biogenesis. Transmembrane segments S1, S2, S3, S5, and S6 initiate translocation, only S1 and S2 strongly (>60%) anchor themselves in the membrane, S5 exhibits signal anchor activity and contains a cryptic cleavage site, and S3 and S6 fail to integrate into the membrane. Elongation of each single-transmembrane construct to include multiple transmembrane segments alters integration and translocation efficiencies, indicating that multiple topogenic determinants cooperate during Kv1. 3 topogenesis and assembly. Several surprising findings emerged from these studies. First, in the presence of T1, the N-terminal recognition domain, S1 was unable to initiate either translocation or membrane integration. As a result, S2 likely functions as the initial signal sequence to establish Kv1.3 N-terminus topology. Second, S4 independently integrates into the membrane. Third, S6 plus the C-terminus of Kv1.3 is a secretory protein but can be converted to a membrane-integrated protein with a correctly oriented, cytosolic C-terminus by linking S6 to S5 and the pore loop. These results have implications for the role of the N-terminus in Kv biogenesis and on the mechanisms of dominant negative suppression of Kv1.3 by truncated Kv1.3 fragments [Tu et al. (1996) J. Biol. Chem. 271, 18904-18911].

No abstract

Dislocation-free vertical GaN pillars in nanoscale were grown on Si (111) surface through self-assembly by molecular-beam epitaxy. No extra catalytic or nanostructural assistance has been employed. These nanorods have a lateral dimension from ≲10 nm to ∼800 nm and a height of ≲50 nm to ≳3 μm protruding above the film, depending on the growth parameters. The top view of the nanorods has a hexagonal shape from scanning electron microscopy. Transmission electron microscopy shows that the nanorods are hexagonal, single crystal GaN along the c-axis. An extra peak at 363 nm originated from nanorods was observed in photoluminescence spectra at 66 K, which is ascribed to the surface states according to the results of surface passivation. Micro-Raman spectroscopy on a single nanorod reveals E1 and E2 modes at 559.0 and 567.4 cm−1, respectively. Large strain was observed in both the transmission electron micrograph and the Raman shift. A possible growth mechanism is discussed.

Voltage-gated K+ channels are tetrameric, but how the four subunits assemble is not known. We analyzed inactivation kinetics and peak current levels elicited for a variety of wild-type and mutant Kv1.3 subunits, expressed singly, in combination, and as tandem constructs, to show that 1) the dominant pathway involves a dimerization of dimers, and 2) dimer-dimer interaction may involve interaction sites that differ from those involved in monomer-monomer association. Moreover, using nondenaturing gel electrophoresis, we detected dimers and tetramers, but not trimers, in the translation reaction of Kv1.3 monomers.

The T1 recognition domains of voltage-gated K(+) (Kv) channel subunits form tetramers and acquire tertiary structure while still attached to their individual ribosomes. Here we ask when and in which compartment secondary and tertiary structures are acquired. We answer this question using biogenic intermediates and recently developed folding and accessibility assays to evaluate the status of the nascent Kv peptide both inside and outside of the ribosome. A compact structure (likely helical) that corresponds to a region of helicity in the mature structure is already manifest in the nascent protein within the ribosomal tunnel. The T1 domain acquires tertiary structure only after emerging from the ribosomal exit tunnel and complete synthesis of the T1-S1 linker. These measurements of ion channel folding within the ribosomal tunnel and its exit port bear on basic principles of protein folding and pave the way for understanding the molecular basis of protein misfolding, a fundamental cause of channelopathies.

Conversion of mechanical energy into electric energy has been demonstrated in GaN nanorods. The measurement was achieved by deflecting GaN nanorods with a conductive atomic force microscope PtIr tip in contact. The mechanism relies on the coupling between piezoelectric and semiconducting properties in GaN nanorod, which creates a strain field and drives the charge flow across the nanorod. The result shown here opens up an opportunity for harvesting electricity from wasted mechanical energies in the ambient environment, which may lead to the realization of self-powered nanodevices.

Folding of membrane proteins begins in the ribosome as the peptide is elongated. During this process, the nascent peptide navigates along 100 Å of tunnel from the peptidyltransferase center to the exit port. Proximal to the exit port is a ‘folding vestibule’ that permits the nascent peptide to compact and explore conformational space for potential tertiary folding partners. The latter occurs for cytosolic subdomains, but has not yet been shown for transmembrane segments. We now demonstrate, using an accessibility assay and an improved, intramolecular crosslinking assay, that the helical transmembrane S3b-S4 hairpin (‘paddle’) of a voltage-gated potassium (Kv) channel, a critical region of the Kv voltage sensor, forms in the vestibule. S3-S4 hairpin interactions are detected at an early stage of Kv biogenesis. Moreover, this vestibule hairpin is consistent with a closed-state conformation of the Kv channel in the plasma membrane.