The Location and Nature of General Anesthetic Binding Sites on the Active Conformation of Firefly Luciferase; A Time Resolved Photolabeling Study

Firefly luciferase is one of the few soluble proteins that is acted upon by a wide variety of general anesthetics and alcohols; they inhibit the ATP–driven production of light. We have used time–resolved photolabeling to locate the binding sites of alcohols during the initial light output, some 200 ms after adding ATP. The photolabel 3-azioctanol inhibited the initial light output with an IC50 of 200 µM, close to its general anesthetic potency. Photoincorporation of [3H]3-azioctanol into luciferase was saturable but weak. It was enhanced 200 ms after adding ATP but was negligible minutes later. Sequencing of tryptic digests by HPLC–MSMS revealed a similar conformation–dependence for photoincorporation of 3-azioctanol into Glu-313, a residue that lines the bottom of a deep cleft (vestibule) whose outer end binds luciferin. An aromatic diazirine analog of benzyl alcohol with broader side chain reactivity reported two sites. First, it photolabeled two residues in the vestibule, Ser-286 and Ile-288, both of which are implicated with Glu-313 in the conformation change accompanying activation. Second, it photolabeled two residues that contact luciferin, Ser-316 and Ser-349. Thus, time resolved photolabeling supports two mechanisms of action. First, an allosteric one, in which anesthetics bind in the vestibule displacing water molecules that are thought to be involved in light output. Second, a competitive one, in which anesthetics bind isosterically with luciferin. This work provides structural evidence that supports the competitive and allosteric actions previously characterized by kinetic studies

The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) Survey Design, Reductions, and Detections

We describe the survey design, calibration, commissioning, and emission-line detection algorithms for the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). The goal of HETDEX is to measure the redshifts of over a million Lyα emitting galaxies between 1.88 < z < 3.52, in a 540 deg2 area encompassing a comoving volume of 10.9 Gpc3. No preselection of targets is involved; instead the HETDEX measurements are accomplished via a spectroscopic survey using a suite of wide-field integral field units distributed over the focal plane of the telescope. This survey measures the Hubble expansion parameter and angular diameter distance, with a final expected accuracy of better than 1%. We detail the project’s observational strategy, reduction pipeline, source detection, and catalog generation, and present initial results for science verification in the Cosmological Evolution Survey, Extended Groth Strip, and Great Observatories Origins Deep Survey North fields. We demonstrate that our data reach the required specifications in throughput, astrometric accuracy, flux limit, and object detection, with the end products being a catalog of emission-line sources, their object classifications, and flux-calibrated spectra

Residues photolabeled in a tryptic fragment of Japanese Firefly Luciferase (340-QGYGLTETT<b>S</b>AIIITPEG<b>D</b>DKPGASGK-366)^a<i>ⁿ</i> identified by LTQ–FT mass spectrometry and MSMS.

a–d<p>Same as <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029854#pone-0029854-t001" target="_blank">Table 1</a>.</p>e<p>Photoincorporation was either in Ser-249 or Ala-250. The latter residue is rarely labeled by aromatic diazirines.</p

Identification of photolabeled residues in the peptide Gln-340 – Lys-366.

<p>Conditions are as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029854#pone-0029854-g004" target="_blank">Fig. 4</a>. <b>A.</b> 3-azibutanol (1 mM) photolabels Asp-358. <b>B.</b> TFD-benzyl alcohol (100 µM) photolabels Ser-349.</p

The structure of Japanese luciferase in the vicinity of the main photolabeled residues.

<p>The structure is shown as a cross section through the luciferin pocket with DSLA bound in the luciferin and ATP sites (2D1S.pdb). Panel A shows a close up view. Panel B is the same view zoomed out (note the 10 Å scale bars) to show the luciferin and ATP pockets. Panel C was obtained by rotating panel B 180° on the y-axis without scaling, viewing the pocket from the opposite side. Cross sections through the protein are capped in white mesh, revealing the residues behind. DSLA is shown with golden carbons. The main photolabeled residues are shown in ball & stick representation with cyan carbons; note that Ser-316 shows two rotamers with each oxygen assigned half occupancy. Important residues for the activity of luciferase that may have been photolabeled are shown with green carbons in stick representation. Hydrogen bonds to ligands and water are shown in panel A by green dashed lines. Surface colors are: white, carbon (except for photolabeled residues, cyan or green); blue, nitrogen; red, oxygen. The upper inset in panel A shows the interaction between Ser-349 and DSLA and the hydrogen bonded water. The lower inset shows the hydrogen bonding network linking the major residues interacting with DSLA through water molecules. Hydrogen bonds shown range from 2.5 to 3.0 Å in length.</p

Ligand-induced changes in the vestibule and grotto region of luciferase.

<p>The “active” DSLA bound (left, 2D1S.pdb) and ATP bound (right, 2D1Q.pdb) structures are compared from the same viewing points. Upper panels show a cross section through the vestibule and grotto region beyond the luciferin binding pocket (compare <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029854#pone-0029854-g007" target="_blank">Fig. 7</a>). The lower panels show the vestibule as viewed from the luciferin pocket; the left panel shows the O10 of DLSA for orientation. Water molecules are shown in red in the +ATP structure and in gold in the DSLA structure (one of the eight water molecules is partially hidden in panel C and is indicated with a circle). The cross-section surface capping is semitransparent. Surface coloring is grey for carbon, red for oxygen and blue for nitrogen. DSLA (gold carbons in A) is a surrogate for luciferin (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029854#pone-0029854-g001" target="_blank">Fig. 1B</a>). Similar changes are seen in American luciferase (3IES.pdb and 3IEP.pdb).</p