ahmet yıldırım wrote:
Dear Justin,

Firstly thanks for your valuable information. Now, is there any error?
Please see the following commands:

protein and ligand are merged by make_ndx

g_sas -f run.xtc -s run.tpr -o area_protein.xvg -n protein_ligand.ndx
Select a group for calculation of surface and a group for output
*select a group: 1 (protein_ligand)*
*select a group: 2 (protein)*
*I have protein SASA.*

g_sas -f run.xtc -s run.tpr -o area_ligand.xvg -n protein_ligand.ndx
Select a group for calculation of surface and a group for output
*select a group: 1 (protein_ligand)*
*select a group: 2 (ligand)
I have ligand SASA.*

g_sas -f run.xtc -s run.tpr -o area_protein_ligand.xvg -n protein_ligand.ndx
Select a group for calculation of surface and a group for output
*select a group: 1 (protein_ligand)*
*select a group: 2 (protein_ligand)
I have protein_ligand SASA.*

*(SASA between protein and ligand)=(protein)+(ligand)-(protein_ligand)*


I'm sorry, I read the first post wrong. Your equation will yield an answer of zero if you do this. I was thinking of your problem backwards. You do indeed want to calculate all of these quantities individually, as you proposed in method #2 previously. That way, you can get the interior cavity surface area, not the exterior components as I was thinking.

-Justin

Thanks

2011/7/3 Justin A. Lemkul <jalem...@vt.edu <mailto:jalem...@vt.edu>>



    ahmet yıldırım wrote:

        Dear users,

        I want to compute SASA between protein and ligand.
        *1.)*
        protein and ligand are merged by make_ndx
        g_sas -f run.xtc -s run.tpr -o protein_ligand.xvg -n
        protein_ligand.ndx
        Select a group for calculation of surface and a group for output
        select a group: 1 (protein+ligand)
        select a group: 2 (ligand)
        is this correct?

        *2.)*
        or
        g_sas -f run.xtc -s run.tpr -o protein_protein.xvg
        Select a group for calculation of surface and a group for output
        select a group: 1 (protein)
        select a group: 2 (protein)
        I have protein SASA.

        g_sas -f run.xtc -s run.tpr -o ligand_ligand.xvg
        Select a group for calculation of surface and a group for output
        select a group: 1 (ligand)
        select a group: 2 (ligand)
        I have ligand SASA.

        protein and ligand are merged by make_ndx
        g_sas -f run.xtc -s run.tpr -o protein_ligand.xvg -n
        protein_ligand.ndx
        Select a group for calculation of surface and a group for output
        select a group: 1 (protein_ligand)
        select a group: 2 (protein_ligand)
        I have protein_ligand SASA.

        (SASA between protein and
        ligand)=(protein)+(ligand)-(__protein_ligand)

        I am confused. which of choices is correct?


    Neither.  Your equation is right, but your method of calculating
    each of the quantities is not.  The group for the surface
    calculation should always be all non-solvent atoms (per the
    instructions in g_sas -h).  The output group can then be whatever
    you like, a subset of that surface.  So you will need three
    calculations (sort of like option #2), but in each case the
    calculation group should always be the protein-ligand merged group.

    -Justin

-- ==============================__==========

    Justin A. Lemkul
    Ph.D. Candidate
    ICTAS Doctoral Scholar
    MILES-IGERT Trainee
    Department of Biochemistry
    Virginia Tech
    Blacksburg, VA
    jalemkul[at]vt.edu <http://vt.edu> | (540) 231-9080
    http://www.bevanlab.biochem.__vt.edu/Pages/Personal/justin
    <http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin>

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--
Ahmet YILDIRIM

--
========================================

Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
MILES-IGERT Trainee
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

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