Calculate structure: Difference between revisions
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After Jmol completes the ''calculate structure'' computation the results of the computation is printed in the upper box of the console. One part of that output is a summary of the different types of secondary structure with each type having a one letter identifier. It is possible for a residue or a segment of residues to be assigned more than one structural type, for this reason the key list given below is rank ordered in decreasing priority of assignment. With bend having the lowest priority in assignment a structure is identified as a bend only if it is not assigned any other structural type. Below is a copy of the summary for myohemerytherin (2mhr): (<scene name='Globular_Proteins/Anti_helix_erythrin2/1'>Restore initial scene</scene>) | After Jmol completes the ''calculate structure'' computation the results of the computation is printed in the upper box of the console. One part of that output is a summary of the different types of secondary structure with each type having a one letter identifier. It is possible for a residue or a segment of residues to be assigned more than one structural type, for this reason the key list given below is rank ordered in decreasing priority of assignment. With bend having the lowest priority in assignment a structure is identified as a bend only if it is not assigned any other structural type. Below is a copy of the summary for myohemerytherin (2mhr): (<scene name='Globular_Proteins/Anti_helix_erythrin2/1'>Restore initial scene</scene>) | ||
The user is urged to use the above directions to open Jmol version 12 and to run the ''calculate structure'' and the accompanying commands so that the resulting display can be compared with the summary below. Without displaying the images generated by ''calculate structure'' and ''calculate hbonds structure'' the activities and comparisons described below can not be performed. After displaying the secondary structure formed by ''calculate structure'' the displayed α-helices and 3<sub>10</sub>-helices can easily be associated with peptide segments in the summary. The turns need some additional explanation. One might expect that the segments in the summary that have one residue, two residues, and three residues are the interior residues of 3-turns, 4-turn and 5-turns, respectively. This is often the case, but in many cases it is not this simple. The turn may overlap or partially overlap with a structure that has higher priority, so that a one residue segment in the summary | The user is urged to use the above directions to open Jmol version 12 and to run the ''calculate structure'' and the accompanying commands so that the resulting display can be compared with the summary below. Without displaying the images generated by ''calculate structure'' and ''calculate hbonds structure'' the activities and comparisons described below can not be performed. After displaying the secondary structure formed by ''calculate structure'' the displayed α-helices and 3<sub>10</sub>-helices can easily be associated with peptide segments in the summary. The turns need some additional explanation. One might expect that the segments in the summary that have one residue, two residues, and three residues are the interior residues of 3-turns, 4-turn and 5-turns, respectively. This is often the case, but in many cases it is not this simple. The turn may overlap or partially overlap with a structure that has higher priority, so that a one residue segment in the summary could represent a 4-turn. Another possibility could be that one turn is nested in a second one. In order to clarify the specific nature of the turn on needs to determine between which two residues the hbond occurs and thereby which type of n-turn is present. Looking closely at a blue colored trace find the dashed line representing a hbond, and hovering over the trace where the dashed line meets the trace reveals the number of the residue that is hydrogen bonded. Go to the other end of the dashed line and determine the residue number at that end. The two numbers should be ''i'' and ''i + n''. Another clarifying determination is to measure the values of the torsional angles (Directions [[Psi_and_Phi_Angles#More Detail on Psi and Phi |to display these angles]]) of the interior residues of the turn. These values can be used to classify the turn as a β-turn or γ-turn. | ||
The second T in the summary is identified as segment A:68_A:69. This turn (Display with green link below) serves to illustrate that most often 4-turns (β-turns) are identified in the summary by their two central residues. Most of the β-turns in myohemerythrin are exceptions to this generalization, but in glycogen phosphorylase (below) it does hold in the majority of cases. Displaying the hbonds after clicking the green link as described below shows that the first residue is hydrogen bonded to the last residue of the turn. This bond qualifies it as a 4-turn, and the phi and psi angles of residues 2 and 3 make it a class I β-turn. Notice, however, that part of residues 67 and 68 are colored white rather than blue. The first T is identified by a two residue segment, but the two residues, A:65_A:66, are the last two in the turn (Display with green link below). Displaying the hbond shows that it is between residues A:63-A:66 which qualifies it for a 4-turn and the torsional angles classify it as type I β-turn. As shown by their coloration the first two residues also qualify as α-helix and are displayed as such since a helix has priority over a turn. The last T identifies a three residue segment with ''calculate hbonds structure'' showing hbonds between 114 and 117 (4-turn and type II β-turn) and between 114 and 118 (5-turn). A β-turn is nested in a 5-turn. Residue 114 is part of the 3<sub>10</sub>-helix so it is not colored blue. | The second T in the summary is identified as segment A:68_A:69. This turn (Display with green link below) serves to illustrate that most often 4-turns (β-turns) are identified in the summary by their two central residues. Most of the β-turns in myohemerythrin are exceptions to this generalization, but in glycogen phosphorylase (below) it does hold in the majority of cases. Displaying the hbonds after clicking the green link as described below shows that the first residue is hydrogen bonded to the last residue of the turn. This bond qualifies it as a 4-turn, and the phi and psi angles of residues 2 and 3 make it a class I β-turn. Notice, however, that part of residues 67 and 68 are colored white rather than blue. The first T is identified by a two residue segment, but the two residues, A:65_A:66, are the last two in the turn (Display with green link below). Displaying the hbond shows that it is between residues A:63-A:66 which qualifies it for a 4-turn and the torsional angles classify it as type I β-turn. As shown by their coloration the first two residues also qualify as α-helix and are displayed as such since a helix has priority over a turn. The last T identifies a three residue segment with ''calculate hbonds structure'' showing hbonds between 114 and 117 (4-turn and type II β-turn) and between 114 and 118 (5-turn). A β-turn is nested in a 5-turn. Residue 114 is part of the 3<sub>10</sub>-helix so it is not colored blue. | ||
