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Re: [modeller_usage] A problem for using loop models: the metal ions came together too close

wayj86 wayj86 wrote:
> After running again I found that althought in some models the overall 
> quality factor did increase, in all of them the metal ions were almost
> merged. Their coordinates were taken too close together. So I was
> wondering was it because the resid for ions were numbered after the
> protein residues (in my model the resid for ions were 312, 313, 314 and
> 315) and loop modelling tended to put them together? If so how should I
> modify the script and multiple alignment file ( in multiple alignment
> file for the target the initial and final residues must be designated,
> like "sequence:MPD:1    : :311   : ::: :", if I hope to redefine the
> resids for ions, some change may also be required in this file) ? Thank
> you very much for any help.

Loop modeling will only move the atoms in the loop itself, and loops by
default are defined as insertions in your alignment of standard amino
acid residues. (You cannot do loop modeling of metal ions, because there
are no statistics collected for non-standard residues.) So what you should
see if you look at the output models is that metal ion coordinates in each
loop model (MPD.BL00010001.pdb, MPD.BL00020001.pdb etc.) are
exactly the same as in the corresponding input model
(MPD.B99990001.pdb). (If this is not the case, something very odd is
happening.) So your problem is not with the loop modeling, but with
the homology modeling.

Without seeing your input files, I will have to guess, but there are two
possibilities. Either the initial coordinates of the metal ions are wrong
(check the MPD.ini file) in which case it's most likely a problem with
your input file (usually using the wrong atom names - Modeller uses
PDB v3 atom naming and so the atom names in your input and MPD.ini
file will be different if this is the problem) or the initial
coordinates are
fine but they are incorrect in the optimized models (MPD.B99990001.pdb
etc.). In the latter case, there must be a problem with your set of
restraints. Modeller generates restraints automatically to keep ligands,
ions etc. in the correct location, but it may be getting confused,
if you have the ions in different positions in each of your templates
(you should probably only use the ions from one template). Alternatively,
you may have conflicts with other user-specified restraints, which you
can check by looking at the violations in the log file.

Finally, I recommend that you use Modeller 9v6.

	Ben Webb, Modeller Caretaker
Modeller mail list: http://salilab.org/mailman/listinfo/modeller_usage