### Script to immerse ubiquitin in a sphere of water just large enough ### to cover it set molname ubq mol new ${molname}.psf mol addfile ${molname}.pdb ### Determine the center of mass of the molecule and store the coordinates set cen [measure center [atomselect top all] weight mass] set x1 [lindex $cen 0] set y1 [lindex $cen 1] set z1 [lindex $cen 2] set max 0 ### Determine the distance of the farthest atom from the center of mass foreach atom [[atomselect top all] get index] { set pos [lindex [[atomselect top "index $atom"] get {x y z}] 0] set x2 [lindex $pos 0] set y2 [lindex $pos 1] set z2 [lindex $pos 2] set dist [expr pow(($x2-$x1)*($x2-$x1) + ($y2-$y1)*($y2-$y1) + ($z2-$z1)*($z2-$z1),0.5)] if {$dist > $max} {set max $dist} } mol delete top ### Solvate the molecule in a water box with enough padding (15 A). ### One could alternatively align the molecule such that the vector ### from the center of mass to the farthest atom is aligned with an axis, ### and then use no padding package require solvate solvate ${molname}.psf ${molname}.pdb -t 15 -o del_water resetpsf package require psfgen mol new del_water.psf mol addfile del_water.pdb readpsf del_water.psf coordpdb del_water.pdb ### Determine which water molecules need to be deleted and use a for loop ### to delete them set wat [atomselect top "same residue as {water and ((x-$x1)*(x-$x1) + (y-$y1)*(y-$y1) + (z-$z1)*(z-$z1))<($max*$max)}"] set del [atomselect top "water and not same residue as {water and ((x-$x1)*(x-$x1) + (y-$y1)*(y-$y1) + (z-$z1)*(z-$z1))<($max*$max)}"] set seg [$del get segid] set res [$del get resid] set name [$del get name] for {set i 0} {$i < [llength $seg]} {incr i} { delatom [lindex $seg $i] [lindex $res $i] [lindex $name $i] } writepsf ${molname}_ws.psf writepdb ${molname}_ws.pdb mol delete top mol new ${molname}_ws.psf mol addfile ${molname}_ws.pdb puts "CENTER OF MASS OF SPHERE IS: [measure center [atomselect top all] weight mass]" puts "RADIUS OF SPHERE IS: $max" mol delete top