[gmx-users] Joining groups for simultaneous analysis in DSSP

[Ali Naqvi]

Hi all,
I have a 25 amino acid peptide that contains 4 phosphoserines. The
forcefield that I have been using is the ff43ap which was modified to
include these groups. So during pdb2gmx I have the rtp and itp files for the
forcefield in the folder in order for the software to find the appropriate
charges. Anyway, simulation is all honkey dory but the problem is in DSSP
analysis which separates the SEP from the protein.

So the entire protein is 252 atoms but when I run the do_dssp program it is
separated into two:
Protein 208 atoms &
SEP is 44 atoms

I can run the dssp separately on the two groups, but since dssp uses
information about adjacent sequence of amino acids, I would say separating
the analysis in the SEP region 16-19 would be wrong as secondary structure
would not be additive like lets say dihedral angles or rmsf.

For results, in the SEP region I am getting the random coil (white as
coloured by xpm2ps) which is equivalent to no secondary structure. Although
I don't have a hard time believing this, just to be a devils advocate of my
own results, I would like to process them together instead of separately. So
my question is how to I join atoms into one group instead of having them
separated?

Cordially,
Ali
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