[modeller_usage] Using frcmod+off non-standard residue in modeller.

Hello,

I'm using Modeller to mutate only. I was wondering how hard it would be to mutate any position into a non-standard residue. I have my residues in Amber format (frcmod+off), and I read that I must create the definitions in CHARMM (RST) format, so modeller understands its topology+charges,etc.

I also have a PDB file and PRMTOP with the non-standard residue. How hard would it be to make this work in Modeller?. Has anybody done it before?

I see that ParmED (for example) can import the Amber files and generate RST files from them, but I didn't fully understand how many files I must modify in modeller, or whether I should use the BLK option, but it is not very well documented how to do so.

Thanks in advance for any info on this. Pedro