Dss - Revision history

Pyadmin: 13 revisions

2014-03-28T01:21:24Z

13 revisions

Speleo3: arguments

2011-06-28T17:29:29Z

arguments

New page

'''dss''' ''d''efines ''s''econdary ''s''tructure based on backbone geometry and hydrogen bonding patterns.

With PyMOL, heavy emphasis is placed on cartoon aesthetics, and so both hydrogen bonding patterns and backbone geometry are used in the assignment process. Depending upon the local context, helix and strand assignments are made based on geometry, hydrogen bonding, or both.

This command will generate results which differ slightly from DSSP and other programs. Most deviations occur in borderline or transition regions. Generally speaking, PyMOL is more strict, thus assigning fewer helix/sheet residues, except for partially distorted helices, which PyMOL tends to tolerate.

WARNING: This algorithm has not yet been rigorously validated.

===USAGE===
dss [selection [, state]]

=== ARGUMENTS ===

* selection = string: atom selection {default: (all)}
* state = integer: state-index if positive number or any of these:
** state = 0: consensus over all states {default}
** state = -1: current state
** state = -2: consensus over effective object states (implemented?)
** state = -3: no consensus, residue gets assignment from earliest state that is not 'L'
** state = -4: consensus over first and last state

===EXAMPLES===
<source lang="python">
# determine secondary structures in
# all loaded objects in PyMOL
dss
</source>

===NOTES===
If you dislike one or more of the assignments made by dss, you can use the alter command to make changes (followed by "rebuild").
For example:
<source lang="python">
# set residues 123-125 as being loops
alter 123-125/, ss='L'

# set the secondary structure of selection (pk1) to beta sheet
alter pk1, ss='S'

# set residue 90 to be alpha-helical
alter 90/, ss='H'

# update the scene in PyMOL to reflect the changes.
rebuild
</source>

====Secondary Structure Determination====
As is typical with PyMOL, the secondary structure assignment engine is ad hoc and empirically tuned to produce desirable aesthetics. Though there are some phi/psi's that are clearly helix/sheet and others that are clearly not, there are certain regions of phi/psi space were the assignment is subjective or arbitrary. In my experience, algorithms based on strict definitions tend to operate poorly in such regions, and so PyMOL's algorithm is "fuzzy" in that there is a grey area where residues may be accepted or rejected as helix/sheet depending upon the surrounding context.

There aren't any hard & fast definitions. But you are welcome to check out the collection of settings beginning with "ss_helix" and "ss_strand", noting that the include and exclude settings are deviations around the target in degrees. If you think PyMOL is incorrectly assigning secondary structure, then you might try varying these.

[[Category:Commands|Dss]]
[[Category:Biochemical_Properties|Dss]]
[[Category:States|Dss]]

Vinnyrose at 13:47, 20 June 2009

2009-06-20T13:47:08Z

New page

===DESCRIPTION===
'''dss''' ''d''efines ''s''econdary ''s''tructure based on backbone geometry and hydrogen bonding patterns.

With PyMOL, heavy emphasis is placed on cartoon aesthetics, and so both hydrogen bonding patterns and backbone geometry are used in the assignment process. Depending upon the local context, helix and strand assignments are made based on geometry, hydrogen bonding, or both.

This command will generate results which differ slightly from DSSP and other programs. Most deviations occur in borderline or transition regions. Generally speaking, PyMOL is more strict, thus assigning fewer helix/sheet residues, except for partially distorted helices, which PyMOL tends to tolerate.

WARNING: This algorithm has not yet been rigorously validated.

===USAGE===
dss selection, state

state = state-index or 0 for all states

===EXAMPLES===
<source lang="python">
# determine secondary structures in
# all loaded objects in PyMOL
dss
</source>

===NOTES===
If you dislike one or more of the assignments made by dss, you can use the alter command to make changes (followed by "rebuild").
For example:
<source lang="python">
# set residues 123-125 as being loops
alter 123-125/, ss='L'

# set the secondary structure of selection (pk1) to beta sheet
alter pk1, ss='S'

# set residue 90 to be alpha-helical
alter 90/, ss='H'

# update the scene in PyMOL to reflect the changes.
rebuild
</source>

====Secondary Structure Determination====
As is typical with PyMOL, the secondary structure assignment engine is ad hoc and empirically tuned to produce desirable aesthetics. Though there are some phi/psi's that are clearly helix/sheet and others that are clearly not, there are certain regions of phi/psi space were the assignment is subjective or arbitrary. In my experience, algorithms based on strict definitions tend to operate poorly in such regions, and so PyMOL's algorithm is "fuzzy" in that there is a grey area where residues may be accepted or rejected as helix/sheet depending upon the surrounding context.

There aren't any hard & fast definitions. But you are welcome to check out the collection of settings beginning with "ss_helix" and "ss_strand", noting that the include and exclude settings are deviations around the target in degrees. If you think PyMOL is incorrectly assigning secondary structure, then you might try varying these.

[[Category:Commands|Dss]]
[[Category:Biochemical_Properties|Dss]]
[[Category:States|Dss]]

Tree at 05:42, 21 February 2005

2005-02-21T05:42:08Z

Tree at 05:41, 21 February 2005

2005-02-21T05:41:44Z

Tree at 05:41, 21 February 2005

2005-02-21T05:41:27Z

New page

===DESCRIPTION===

"dss" defines secondary structure based on backbone geometry
and hydrogen bonding patterns.

With PyMOL, heavy emphasis is placed on cartoon aesthetics, and so
both hydrogen bonding patterns and backbone geometry are used in
the assignment process. Depending upon the local context, helix
and strand assignments are made based on geometry, hydrogen
bonding, or both.

This command will generate results which differ slightly from DSSP
and other programs. Most deviations occur in borderline or
transition regions. Generally speaking, PyMOL is more strict, thus
assigning fewer helix/sheet residues, except for partially
distorted helices, which PyMOL tends to tolerate.

WARNING: This algorithm has not yet been rigorously validated.

===USAGE===

dss selection, state

state = state-index or 0 for all states

===EXAMPLES===
dss

===NOTES===
If you dislike one or more of the assignments made by dss, you can
use the alter command to make changes (followed by "rebuild").
For example:
alter 123-125/, ss='L'
alter pk1, ss='S'
alter 90/, ss='H'
rebuild

[[:Category:Commands dss]]

← Older revision		Revision as of 05:42, 21 February 2005
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	rebuild		rebuild

−	[[Category:Commands dss]]	+	[[Category:Commands\|dss]]

← Older revision		Revision as of 05:41, 21 February 2005
Line 36:		Line 36:
	rebuild		rebuild

−	[[:Category:Commands dss]]	+	[[Category:Commands dss]]

← Older revision	Revision as of 01:21, 28 March 2014
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