Property Selectors

Property Selectors

PyMOL reads data files written in PDB, MOL/SDF, Macromodel, ChemPy Model, and Tinker XYZ formats. Some of the data fields in these formats allow PyMOL to assign properties to atoms. You can group and select atoms according to these properties using property selectors and identifiers: the selectors correspond to the fields in the data files, and the identifiers correspond to the target words to match, or the target numbers to compare.

General

The items in a list of identifiers are separated by plus signs (+) only. Do not add spaces within a list of identifiers. The selector resi takes (+)-separated lists of identifiers, as in

PyMOL> select nterm, resi 1+2+3

or, alternatively, it may take a range given with a dash

PyMOL> select nterm, resi 1-3

However, you will get an error message if you try to combine a list and a range in an identifier to a resi as in

PyMOL> select mistake, resi 1-3+6      <--This is WRONG

The identifier for a blank field in an input file is and empty pair of quotes

PyMOL> select unstruct, ss ""   # A named selection is created
                                # to contain all atoms that are not assigned 
                                # a secondary structure.

Property Selector Table

Most property selectors select matches to their identifiers

Matching Property Selector	Short Form Selector	Identifier and Example
symbol	e.	chemical-symbol-list list of 1- or 2-letter chemical symbols from the periodic table PyMOL> select polar, symbol o+n
name	n.	atom-name-list list of up to 4-letter codes for atoms in proteins or nucleic acids PyMOL> select carbons, name ca+cb+cg+cd
resn	r.	residue-name-list list of 3-letter codes for amino acids PyMOL> select aas, resn asp+glu+asn+gln or list of up to 2-letter codes for nucleic acids PyMOL> select bases, resn a+g
resi	i.	residue-identifier-list list of up to 4-digit residue numbers PyMOL> select mults10, resi 1+10+100+1000 residue-identifier-range PyMOL> select nterm, resi 1-10
alt	alt	alternate-conformation-identifier-list list of single letters PyMOL> select altconf, alt a+""
chain	c.	chain-identifier-list list of single letters or sometimes numbers PyMOL> select firstch, chain a
segi	s.	segment-identifier-list list of up to 4 letter identifiers PyMOL> select ligand, segi lig
flag	f.	flag-number a single integer from 0 to 31 PyMOL> select f1, flag 0
numeric_type	nt.	type-number a single integer PyMOL> select type1, nt. 5
text_type	tt.	type-string a list of up to 4 letter codes PyMOL> select subset, text_type HA+HC
id	id	external-index-number a single integer PyMOL> select idno, id 23
index	idx.	internal-index-number a single integer PyMOL> select intid, index 11
ss	ss	secondary-structure-type list of single letters PyMOL> select allstrs, ss h+s+l+""

Numeric Selector Table

Other property selectors select by comparison to numeric identifiers

Numeric Selector	Short Form	Argument and Example
b	b	comparison-operator b-factor-value a real number PyMOL> select fuzzy, b > 10
q	q	comparison-operator occupancy-value a real number PyMOL> select lowcharges, q <0.50
formal_charge	fc.	comparison-operator formal charge-value an integer PyMOL> select doubles, fc. = -1
partial_charge	pc.	comparison-operator partial charge-value a real number PyMOL> select hicharges, pc. > 1

User Notes

Select by PDB Assigned Atom Number

To select atoms by their PDB ATOM number, use the id selector:

 select Nt, id 1-30

makes a new selection called Nt and puts in it the first 30 atoms (assuming your PDB starts numbering at 1).

Selecting via a Negative Identifier

If you have a residue id < 0, eg. resi -55, then you have to escape the minus sign or renumber the atoms:

select i. \-55

Alternate Locations

Select All Alternate Locations

• To select all residues with alternate locations (alt, alt loc), simply do:

select aa, not alt ""

Try it on 1CBN.

Select All Alternate Locations Except the A-Locations

• To select and remove all atoms with alternate locations (ALT, alt loc) that aren't the A record try the following. This removes all alt locations that are not the original A location. For example given the following pdb record,

 1 ATOM    949  N   ARG A 124       6.039   8.484   9.313  1.00  9.82           N
 2 ATOM    950  CA  ARG A 124       5.839   7.071   8.980  1.00 10.05           C
 3 ATOM    951  C   ARG A 124       6.009   6.809   7.493  1.00  9.18           C
 4 ATOM    952  O   ARG A 124       5.803   7.715   6.648  1.00  9.06           O
 5 ATOM    953  CB  ARG A 124       4.437   6.660   9.425  1.00 10.61           C
 6 ATOM    954  CG AARG A 124       4.381   6.539  10.955  0.50 12.54           C
 7 ATOM    955  CG BARG A 124       4.170   6.743  10.930  0.50 14.58           C
 8 ATOM    956  CD AARG A 124       2.996   6.418  11.561  0.50 11.86           C
 9 ATOM    957  CD BARG A 124       2.700   7.091  11.242  0.50 17.41           C
10 ATOM    958  NE AARG A 124       2.110   7.506  11.144  0.50 13.01           N
11 ATOM    959  NE BARG A 124       2.229   6.746  12.588  0.50 19.94           N
12 ATOM    960  CZ AARG A 124       0.912   7.729  11.654  0.50 12.21           C
13 ATOM    961  CZ BARG A 124       2.123   5.510  13.067  0.50 21.42           C
14 ATOM    962  NH1AARG A 124       0.433   6.958  12.627  0.50 12.93           N
15 ATOM    963  NH1BARG A 124       2.470   4.470  12.319  0.50 24.35           N
16 ATOM    964  NH2AARG A 124       0.185   8.735  11.188  0.50 11.89           N
17 ATOM    965  NH2BARG A 124       1.658   5.310  14.313  0.50 18.28           N

the command below will remove the (not A so) B-locations (lines 7, 9, 11, 13, 15, 17).

# select & remove all non A altlocs
remove not (alt ''+A)
# reset the PDB information
alter all, alt=''

See also, removeAlt for a script to do this for you.

See Also

• Single-word Selectors
• Selection Macros
• Selection_Algebra