UCSF-Chimera/C3/Structure-Analysis/English-timed

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Time Narration
00:01 Welcome to this tutorial on Structure Analysis.
00:05 In this tutorial, we will learn to : measure distance between atoms in the structure, show Hydrogen bonds, identify non-polar interactions,
00:16 and rotate bonds in the residues to get different rotamers.
00:21 To follow this tutorial, you should be familiar with Chimera interface. If not, for relevant tutorials, please visit our website.
00:30 Here, I am using Ubuntu OS version. 14.04 ,Chimera version 1.10.2 , Mozilla firefox browser 42.0 and a working internet connection.
00:46 Here, I have opened a Chimera window.
00:49 Using command line, open a structure of Squalene Synthase. It is a Transferace enzyme with a pdb code 3w7f.
01:00 On the command line, type Open space 3w7f. Press Enter.
01:09 A model of the enzyme is displayed on the panel.
01:12 Change the display to Interactive 1, using Presets menu.
01:18 The protein is displayed as two copies.
01:21 To delete one of the copies, type delete colon dot a, press Enter.
01:29 To delete solvent molecules from the structure, type: delete solvent. Press Enter.
01:37 In this structure, the ligand is farnesyl thiopyrophosphate.
01:43 Label the ligand residues using commands. Type: rlabel space ligand. Press Enter.
01:53 There are two farnesyl thiopyrophosphate, that is, FPS for short in this structure.
02:01 The structures are shown in sticks display.
02:05 Rotate the structure and zoom-in.
02:08 There are several side chains that can donate hydrogen bonds to phosphate oxygens of FPS.
02:15 Place the cursor over the atoms in the side-chain residues.
02:21 Locate Serine 21 residue.
02:23 Now, let's measure the distance between oxygen of Serine 21 and nearest phosphate oxygen of FPS.
02:32 To measure the distance, select oxygen of Serine 21 residue.
02:37 While pressing the CTRL key, click on the side chain oxygen of Serine 21.
02:43 While pressing CTRL and Shift keys simultaneously, double-click on the nearest phosphate oxygen of FPS.
02:52 Select Show Distance from the context menu.
02:56 Observe the panel. The distance between two atoms is displayed. Clear selection.
03:04 Similarly, measure distance between side-chain oxygen of Tyrosine and the same phosphate oxygen of FPS.
03:15 The distances seem consistent with hydrogen bonds.
03:20 Hydrogen bonds with donor and acceptor distances of 2.2 to 2.5 Angstroms are classified as strong, 2.5 to 3.2 as moderate, 3.2 to 4.0 as weak.
03:36 Now, select the ligand using Select menu.
03:40 Scroll down to residue option, click on FPS from the sub-menu.
03:46 The easy way to find hydrogen bonds formed by FPS is to use Find Hydrogen bond feature from Tools menu.
03:55 Click on FindHbond in the Structure Analysis option.
04:01 A H-Bond Parameters dialog opens.
04:05 Fix the color of the hydrogen bond by clicking on the colored box.
04:09 Fix the line width to 3.0 for a thicker line.
04:13 Click on the check box against Label Hydrogen bond with distance.
04:21 Click on Only find H-bonds with at least one end selected.
04:26 And, click on Write information to reply log.
04:31 Click on OK button.
04:33 Observe the panel. Hydrogen bonds are shown as pseudo-bonds of specified color and line width.
04:42 Details of the bonds can be viewed on the Reply log.
04:45 Open Reply log using Favorites menu.
04:49 Information about each hydrogen bond is given here.
04:53 Close the dialog box.
04:55 If you want to remove the hydrogen bonds from the structure- on the command line, type: The Tilda symbol followed by hbond. Press Enter.
05:07 There is another feature in the Tools menu, under Structure Analysis option.
05:13 It is Findclashes/contacts. A dialog box opens.
05:19 This feature identifies non-polar interactions such as Clashes and Contacts.
05:26 Clashes are unfavorable interactions where atoms are too close together.
05:33 Contacts are all direct interactions, polar and non-polar, favorable and unfavorable (including clashes).
05:43 Let us identify contacts of the FPS residues with all other atoms.
05:48 Select FPS residue using Select menu.
05:52 Click on Designate in the Find Clashes/Contacts dialog box.
05:58 It shows 48 atoms designated.
06:02 Click on the radio button against “All other atoms”.
06:06 Set the Clash/Contact Parameters to default Contact.
06:11 Under Treatment of Clash/Contact Atoms, click on the following check boxes. Select, Draw pseudo-bonds, If endpoint atom hidden, and Write information to reply log.
06:27 Click on OK button. Observe the panel.
06:32 All the contacts of FPS residues are shown.
06:37 Open the Reply Log. . Atom-atom contacts are listed here.
06:44 Close the dialog box.
06:46 Now let's display some clashes.
06:49 Let us focus on the residue Tyrosine 248.
06:54 On the command line, type: focus space colon 248. Press Enter.
07:03 Clear the selection.
07:06 Now select Tyrosine 248 residue.
07:10 While pressing the CTRL key, click on any atom in Tyrosine 248.
07:15 Press up-arrow key on the keyboard to select the entire molecule.
07:20 Now, we will rotate the side-chain Tyrosine 248 interactively and check for Clashes.
07:27 Display residues within 4 Angstroms of Tyrosine 248.
07:32 On the command line, type: display, disp space colon 248 space z less than four. (disp :248 z<4) Press Enter.
07:45 To display the clashes, select FindClashes/Contacts option from the Tools menu.
07:53 click on Designate.
07:55 Click the button against “All other atoms”.
07:59 Set the Clash/Contact Parameters to Clash. . The Treatment of Clash/Contact Atoms to Select, Draw pseudobonds, If end point atom hidden.
08:11 And set the Frequency of Checking to Continuously.
08:15 Hide the dialog box.
08:18 To rotate the side-chain of Tyrosine 248 interactively-
08:22 while pressing CTRL key, double-click on the bond that is attached to the ribbon.
08:29 Choose rotate bond option from the context menu.
08:33 A Build structure dialog opens.
08:36 Rotate the bond by dragging the pointer on the dial.
08:41 Alternatively, click on the black arrowheads to edit the angle values.
08:47 Observe the panel. As the side-chain moves, new pseudo-bonds are formed or disappear.
08:55 To revert bond back to the original position: click the entry under Bond. Choose Revert.
09:03 Again click on the bond then Deactivate to make the bond no longer rotate-able.
09:09 Close the dialog box.
09:11 We can compare all the rotamers of Tyrosine 248 using the option in the Tools menu.
09:18 First select Tryrosine 248.
09:22 Click on Tools menu, scroll down to Structure editing.
09:26 Click on Rotamers option.
09:29 In the Rotamer dialog box, select Dunbrack from the rotamer library.
09:36 Click on OK button.
09:38 The rotamers are shown as wire representation on the panel.
09:43 Another dialog opens. Click on the lines in the dialog box to display the rotamer. Observe the panel.
09:52 We can also detect Clash and hydrogen bonds for the rotamers.
09:58 Click on Columns ,then Add. Select Clashes.
10:03 Click on OK in the dialog box.
10:06 Now, to add Hydrogen bonds: click on Columns, scroll down to Add, and select hydrogen bonds.
10:15 Click on OK in the Hydrogen bonds dialog box.
10:19 Observe the dialog, two new columns are added.
10:24 Now each rotamer forms several Clashes but no hydrogen bonds.
10:30 Try finding rotamers by rotating bonds in a different residue.
10:35 Let's summarize. In this tutorial, we have learnt to- measure distance between atoms in the structure,
10:43 show Hydrogen bonds, identify non-polar interactions,
10:48 rotate bonds in the residues to find clashes and contacts and compare different rotamers.
10:56 For the assignment- open a structure of Squalene Synthase, pdb code 3w7f .
11:03 Rotate bonds in Tyrosine 41, residue to determine Clashes and Contacts. And compare the rotamers.
11:11 The video at the following link summarizes the Spoken Tutorial project. Please download and watch it.
11:17 The Spoken Tutorial project team conducts workshops and gives certificates for those who pass an on line test. For more details, please write to us.
11:27 Spoken Tutorial project is funded by NMEICT, MHRD, Government of India. More information on this mission is available at the link shown.
11:37 This is Snehalatha from IIT Bombay, signing off. Thank you for joining.

Contributors and Content Editors

Jyotisolanki, PoojaMoolya, Sandhya.np14