A New Transmitted Reference Pulse Cluster Based Ultra-Wideband Transmitter Design

An energy efficient ultra-wideband (UWB) transmitter based on the novel transmitted reference pulse cluster (TRPC) modulation scheme is presented. The TRPC-UWB transmitter integrates, namely, wideband active baluns, wideband I-Q modulator based up-conversion mixer, and differential to single-ended converter. The integrated circuits of TRPC-UWB front end is designed and implemented in the 130-nm CMOS process technology. the measured worst-case carrier leakage suppression is 22.4 dBc, while the single sideband suppression is higher than 31.6 dBc, operating at the frequency from 3.1 GHz to 8.2 GHz. With adjustable data rate of 10 to 300 Mbps, the transmitter achieves a high energy efficiency of 38.4 pJ/pulse.Comment: 4 page, 8 figure

Structural and Mechanistic Studies on à-Amino ?-Carboxymuconate î-Semialdehyde Decarboxylase and à-Aminomuconate î-Semialdehyde Dehydrogenase

α-Amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD) and α-aminomuconate-ε-semialdehyde dehydrogenase (AMSDH) are two neighboring enzymes in the L-tryptophan and 2-nitrobenzoic acid degradation pathways. The substrates of the two enzymes, α-amino-β-carboxymuconate-ε-semialdehyde (ACMS) and α-aminomuconate-ε-semialdehyde (2-AMS), are unstable and spontaneously decay to quinolinic acid and picolinic acid, respectively. ACMSD utilizes a divalent zinc metal as cofactor and is a member of the amidohydrolase superfamily. In this dissertation work, we have identified an important histidine residue in the active site that plays dual roles in tuning metal selectivity and activating a metal bound water ligand using mutagenesis, resonance Raman, EPR, crystallography, and ICP metal analysis techniques. The crystal structures of ACMSD from Pseudomonas fluorescens (PfACMSD) have been solved as homodimers in our laboratory while human ACMSD (hACMSD) was annotated as a monomer by another group. To resolve this structural difference, we used two conserved active site arginine residues as probes to study the oligomeriztion state of ACMSD and demonstrated that these two arginine residues are involved in substrate binding and that both Pf- and h- ACMSD are catalytically active only in the dimeric state. Subsequently, we solved the crystal structure of hACMSD and found it to be a homodimer in both catalytically active and inhibitor-bound forms. AMSDH is an NAD+ dependent enzyme and belongs to the aldehyde dehydrogenase superfamily. Due to the high instability of its substrate, AMSDH has not been studied at the molecular level prior to our work. We have cloned and expressed PfAMSDH in E. coli. The purified protein has high activity towards both 2-AMS and 2-hydroxymuconate semialdehyde (2-HMS), a stable substrate analog. We have successfully crystallized AMSDH with/without NAD+ and solved the crystal structure at up to 1.95 Å resolution. Substrate bound ternary complex structures were obtained by soaking the NAD+ containing crystals with 2-AMS or 2-HMS. Notably, two covalently bound catalytic intermediates were captured and characterized using a combination of crystallography, stopped-flow, single crystal spectroscopy, and mass spectrometry. The first catalytic working model of AMSDH has been proposed based on our success in structural and spectroscopic characterization of the enzyme in five catalytically relevant states in this dissertation work

Structural and Mechanistic Studies on α-Amino β-Carboxymuconate ε-Semialdehyde Decarboxylase and α-Aminomuconate ε-Semialdehyde Dehydrogenase

α-Amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD) and α-aminomuconate-ε-semialdehyde dehydrogenase (AMSDH) are two neighboring enzymes in the L-tryptophan and 2-nitrobenzoic acid degradation pathways. The substrates of the two enzymes, α-amino-β-carboxymuconate-ε-semialdehyde (ACMS) and α-aminomuconate-ε-semialdehyde (2-AMS), are unstable and spontaneously decay to quinolinic acid and picolinic acid, respectively. ACMSD utilizes a divalent zinc metal as cofactor and is a member of the amidohydrolase superfamily. In this dissertation work, we have identified an important histidine residue in the active site that plays dual roles in tuning metal selectivity and activating a metal bound water ligand using mutagenesis, resonance Raman, EPR, crystallography, and ICP metal analysis techniques. The crystal structures of ACMSD from Pseudomonas fluorescens (PfACMSD) have been solved as homodimers in our laboratory while human ACMSD (hACMSD) was annotated as a monomer by another group. To resolve this structural difference, we used two conserved active site arginine residues as probes to study the oligomeriztion state of ACMSD and demonstrated that these two arginine residues are involved in substrate binding and that both Pf- and h- ACMSD are catalytically active only in the dimeric state. Subsequently, we solved the crystal structure of hACMSD and found it to be a homodimer in both catalytically active and inhibitor-bound forms. AMSDH is an NAD+ dependent enzyme and belongs to the aldehyde dehydrogenase superfamily. Due to the high instability of its substrate, AMSDH has not been studied at the molecular level prior to our work. We have cloned and expressed PfAMSDH in E. coli. The purified protein has high activity towards both 2-AMS and 2-hydroxymuconate semialdehyde (2-HMS), a stable substrate analog. We have successfully crystallized AMSDH with/without NAD+ and solved the crystal structure at up to 1.95 Å resolution. Substrate bound ternary complex structures were obtained by soaking the NAD+ containing crystals with 2-AMS or 2-HMS. Notably, two covalently bound catalytic intermediates were captured and characterized using a combination of crystallography, stopped-flow, single crystal spectroscopy, and mass spectrometry. The first catalytic working model of AMSDH has been proposed based on our success in structural and spectroscopic characterization of the enzyme in five catalytically relevant states in this dissertation work

Modeling mGluR1 Mediated Synaptic Depression in Cerebellar Purkinje Cells

In our previous study, we have successfully simulated mGluR1 mediated sEPSP based on experimental and is associated with parallel fiber – Purkinje cell LTD [1, 2, 3]. Recent studies have shown that the mGluR1 mediated sEPSP is generated by calcium signaling through the TRPC channel which is crucial in cerebellar LTD induction [4]. Behavior study using mutant mice that lack this type of LTD has shown no motor learning impairment [5]. We hypothesize that cerebellar TRPC mediated synaptic depression shifts the excitatory and inhibitory balance to down regulate ongoing simple-spike activity. To test our hypothesis we modified our previous model of a Purkinje cell [6, 7] to have TRPC channel current signal linked to the AMPA channel conductance through Kinetikit [8]

Cerebellar nuclei neurons show only small excitatory responses to optogenetic olivary stimulation in transgenic mice: in vivo and in vitro studies

BACKGROUND: To study the olivary input to the cerebellar nuclei (CN) we used optogenetic stimulation in transgenic mice expressing channelrhodopsin-2 (ChR2) in olivary neurons. We obtained in vivo extracellular Purkinje cell (PC) and CN recordings in anesthetized mice while stimulating the contralateral inferior olive (IO) with a blue laser (single pulse, 10 - 50 ms duration). Peri-stimulus histograms were constructed to show the spike rate changes after optical stimulation. Among 29 CN neurons recorded, 15 showed a decrease in spike rate of variable strength and duration, and only 1 showed a transient spiking response. These results suggest that direct olivary input to CN neurons is usually overridden by stronger Purkinje cell inhibition triggered by climbing fiber responses. To further investigate the direct input from the climbing fiber collaterals we also conducted whole cell recordings in brain slices, where we used local stimulation with blue light. Due to the expression of ChR2 in Purkinje cell axons as well as the IO in our transgenic line, strong inhibitory responses could be readily triggered with optical stimulation (13 of 15 neurons). After blocking this inhibition with GABAzine, only in 5 of 13 CN neurons weak excitatory responses were revealed. Therefore our in vitro results support the in vivo findings that the excitatory input to CN neurons from climbing fiber collaterals in adult mice is masked by the inhibition under normal conditions