Regional increase in the expression of the BCAT proteins in Alzheimer's disease brain: Implications in glutamate toxicity

BACKGROUNDThe human branched chain aminotransferases (hBCATm, mitochondrial and hBCATc, cytosolic) are major contributors to brain glutamate production. This excitatory neurotransmitter is thought to contribute to neurotoxicity in neurodegenerative conditions such as Alzheimer's disease (AD) but the expression of hBCAT in this disease has not previously been investigated.OBJECTIVEThe objective of investigating hBCAT expression is to gain insight into potential metabolic pathways that may be dysregulated in AD brain, which would contribute to glutamate toxicity.METHODSWestern blot analysis and immunohistochemistry were used to determine the expression and localization of hBCAT in postmortem frontal and temporal cortex from AD and matched control brains.RESULTSWestern blot analysis demonstrated a significant regional increase in hBCATc expression in the hippocampus (↑ 36%; p-values of 0.012), with an increase of ↑ 160% reported for hBCATm in the frontal and temporal cortex (p-values = 4.22 × 10-4 and 2.79 × 10-5, respectively) in AD relative to matched controls, with evidence of post-translational modifications to hBCATm, more prominent in AD samples. Using immunohistochemistry, a significant increase in immunopositive labelling of hBCATc was observed in the CA1 and CA4 region of the hippocampus (p-values = 0.011 and 0.026, respectively) correlating with western blot analysis. Moreover, the level of hBCATm in the frontal and temporal cortex correlated significantly with disease severity, as indicated by Braak staging (p-values = 5.63 × 10-6 and 9.29 × 10-5, respectively).CONCLUSIONThe expression of the hBCAT proteins is significantly elevated in AD brain. This may modulate glutamate production and toxicity, and thereby play a role in the pathogenesis of the disease

Mid-infrared resolution of a 3 AU-radius debris disk around Zeta Leporis

We present subarcsecond-resolution mid-infrared images of the debris disk surrounding the 230 Myr- old A star Zeta Lep. Our data obtained with T-ReCS at Gemini South show the source to be unresolved at 10.4 microns but clearly extended at 18.3 microns. Quadratic subtraction of the PSF profile from that of Zeta Lep implies a characteristic radius for the dust disk of 3 AU, which is comparable in size to our solar system's asteroid belt. Simple models suggest that the 18 micron flux is well approximated by two contiguous annuli of mid-infrared-emitting dust from 2-4 and 4-8 AU with a 3:1 flux ratio for the annuli, respectively. We consider two scenarios for the collisions that must be resupplying the dust population: (1) continuous "steady state" grinding of planetesimals, and (2) an isolated cataclysmic collision. We determine that radiation pressure and subsequent collisions are the dominant determinants of the disk morphology in either case, and that Poynting-Robertson drag is comparatively insignificant.Comment: 4 pages, 1 figure, accepted for publication in ApJ Letter

The ROTSE-III Robotic Telescope System

The observation of a prompt optical flash from GRB990123 convincingly demonstrated the value of autonomous robotic telescope systems. Pursuing a program of rapid follow-up observations of gamma-ray bursts, the Robotic Optical Transient Search Experiment (ROTSE) has developed a next-generation instrument, ROTSE-III, that will continue the search for fast optical transients. The entire system was designed as an economical robotic facility to be installed at remote sites throughout the world. There are seven major system components: optics, optical tube assembly, CCD camera, telescope mount, enclosure, environmental sensing & protection and data acquisition. Each is described in turn in the hope that the techniques developed here will be useful in similar contexts elsewhere.Comment: 19 pages, including 4 figures. To be published in PASP in January, 2003. PASP Number IP02-11

The Roles of the Chaperone-like Protein CpeZ and the Phycoerythrobilin Lyase CpeY in Phycoerythrin Biogenesis

Phycoerythrin (PE) present in the distal ends of light-harvesting phycobilisome rods in Fremyella diplosiphon (Tolypothrix sp. PCC 7601) contains five phycoerythrobilin (PEB) chromophores attached to six cysteine residues for efficient green light capture for photosynthesis. Chromophore ligation on PE subunits occurs through bilin lyase catalyzed reactions, but the characterization of the roles of all bilin lyases for phycoerythrin is not yet complete. To gain a more complete understanding about the individual functions of CpeZ and CpeY in PE biogenesis in cyanobacteria, we examined PE and phycobilisomes purified from wild type F. diplosiphon, cpeZ and cpeY knockout mutants. We find that the cpeZ and cpeY mutants accumulate less PE than wild type cells. We show that in the cpeZ mutant, chromophorylation of both PE subunits is affected, especially the Cys-80 and Cys-48/Cys-59 sites of CpeB, the beta-subunit of PE. The cpeY mutant showed reduced chromophorylation at Cys-82 of CpeA. We also show that, in vitro, CpeZ stabilizes PE subunits and assists in refolding of CpeB after denaturation. Taken together, we conclude that CpeZ acts as a chaperone-like protein, assisting in the folding/stability of PE subunits, allowing bilin lyases such as CpeY and CpeS to attach PEB to their PE subunit

Observations of the Optical Counterpart to XTE J1118+480 During Outburst by the ROTSE-I Telescope

The X-ray nova XTE J1118+480 exhibited two outbursts in the early part of 2000. As detected by the Rossi X-ray Timing Explorer (RXTE), the first outburst began in early January and the second began in early March. Routine imaging of the northern sky by the Robotic Optical Transient Search Experiment (ROTSE) shows the optical counterpart to XTE J1118+480 during both outbursts. These data include over 60 epochs from January to June 2000. A search of the ROTSE data archives reveal no previous optical outbursts of this source in selected data between April 1998 and January 2000. While the X-ray to optical flux ratio of XTE J1118+480 was low during both outbursts, we suggest that they were full X-ray novae and not mini-outbursts based on comparison with similar sources. The ROTSE measurements taken during the March 2000 outburst also indicate a rapid rise in the optical flux that preceded the X-ray emission measured by the RXTE by approximately 10 days. Using these results, we estimate a pre-outburst accretion disk inner truncation radius of 1.2 x 10^4 Schwarzschild radii.Comment: 9 pages, 1 table, 2 figure

CpeT is the Phycoerythrobilin Lyase for Cys-165 on Beta-Phycoerythrin from Fremyella Diplosiphon and the Chaperone-like Protein CpeZ Greatly Improves its Activity.

Bilin lyases are enzymes which ligate linear tetrapyrrole chromophores to specific cysteine residues on light harvesting proteins present in cyanobacteria and red algae. The lyases responsible for chromophorylating the light harvesting protein phycoerythrin (PE) have not been fully characterized. In this study, we explore the role of CpeT, a putative bilin lyase, in the biosynthesis of PE in the cyanobacterium Fremyella diplosiphon. Recombinant protein studies show that CpeT alone can bind phycoerythrobilin (PEB), but CpeZ, a chaperone-like protein, is needed in order to correctly and efficiently attach PEB to the beta-subunit of PE. MS analyses of the recombinant beta-subunit of PE coexpressed with CpeT and CpeZ show that PEB is attached at Cys-165. Purified phycobilisomes from a cpeT knockout mutant and wild type (WT) samples from F. diplosiphon were analyzed and compared. The cpeT mutant contained much less PE and more phycocyanin than WT cells grown under green light, conditions which should maximize the production of PE. In addition, Northern blot analyses showed that the cpeCDESTR operon mRNAs were upregulated while the cpeBcpeA mRNAs were downregulated in the cpeT mutant strain when compared with WT, suggesting that CpeT may also play a direct or indirect regulatory role in transcription of these operons or their mRNA stability, in addition to its role as a PEB lyase for Cys-165 on beta-PE

ROTSE All Sky Surveys for Variable Stars I: Test Fields

The ROTSE-I experiment has generated CCD photometry for the entire Northern sky in two epochs nightly since March 1998. These sky patrol data are a powerful resource for studies of astrophysical transients. As a demonstration project, we present first results of a search for periodic variable stars derived from ROTSE-I observations. Variable identification, period determination, and type classification are conducted via automatic algorithms. In a set of nine ROTSE-I sky patrol fields covering about 2000 square degrees we identify 1781 periodic variable stars with mean magnitudes between m_v=10.0 and m_v=15.5. About 90% of these objects are newly identified as variable. Examples of many familiar types are presented. All classifications for this study have been manually confirmed. The selection criteria for this analysis have been conservatively defined, and are known to be biased against some variable classes. This preliminary study includes only 5.6% of the total ROTSE-I sky coverage, suggesting that the full ROTSE-I variable catalog will include more than 32,000 periodic variable stars.Comment: Accepted for publication in AJ 4/00. LaTeX manuscript. (28 pages, 11 postscript figures and 1 gif

Review of Top Quark Physics Results

As the heaviest known fundamental particle, the top quark has taken a central role in the study of fundamental interactions. Production of top quarks in pairs provides an important probe of strong interactions. The top quark mass is a key fundamental parameter which places a valuable constraint on the Higgs boson mass and electroweak symmetry breaking. Observations of the relative rates and kinematics of top quark final states constrain potential new physics. In many cases, the tests available with study of the top quark are both critical and unique. Large increases in data samples from the Fermilab Tevatron have been coupled with major improvements in experimental techniques to produce many new precision measurements of the top quark. The first direct evidence for electroweak production of top quarks has been obtained, with a resulting direct determination of $V_{tb}$. Several of the properties of the top quark have been measured. Progress has also been made in obtaining improved limits on potential anomalous production and decay mechanisms. This review presents an overview of recent theoretical and experimental developments in this field. We also provide a brief discussion of the implications for further efforts.Comment: 119 pages, 55 figure

CpeF is the Bilin Lyase that Ligates the Doubly Linked Phycoerythrobilin on Phycoerythrin in the Cyanobacterium Fremyella Diplosiphon

Phycoerythrin (PE) is a green light-absorbing protein present in the light-harvesting complex of cyanobacteria and red algae. The spectral characteristics of PE are due to its prosthetic groups, or phycoerythrobilins (PEBs), that are covalently attached to the protein chain by specific bilin lyases. Only two PE lyases have been identified and characterized so far, and the other bilin lyases are unknown. Here, using in silico analyses, markerless deletion, biochemical assays with purified and recombinant proteins, and site-directed mutagenesis, we examined the role of a putative lyase-encoding gene, cpeF, in the cyanobacterium Fremyella diplosiphon. Analyzing the phenotype of the cpeF deletion, we found that cpeF is required for proper PE biogenesis, specifically for ligation of the doubly linked PEB to Cys-48/Cys-59 residues of the CpeB subunit of PE. We also show that in a heterologous host, CpeF can attach PEB to Cys-48/Cys-59 of CpeB, but only in the presence of the chaperone-like protein CpeZ. Additionally, we report that CpeF likely ligates the A ring of PEB to Cys-48 prior to the attachment of the D ring to Cys-59. We conclude that CpeF is the bilin lyase responsible for attachment of the doubly ligated PEB to Cys-48/Cys-59 of CpeB and together with other specific bilin lyases contributes to the post-translational modification and assembly of PE into mature light-harvesting complexes