help requested with modified amino acid param files

[Jennifer Ekstrom]

Hello,

I'm refining a protein with a pyruvate group (modified amino 
acid) bound through a peptide link to the N-terminus of 
the protein chain.  I've downloaded topology and parameter
files from the library, but I'm having problems getting 
through check without crashing.  If I include the pvl 
group in the segment with the protein chain it is part 
of, I get missing bond parameter errors (bond energy
constant missing & target bond length missing). 

 %CODBON-ERR: missing bond parameters %%%%%%%%%%%%%%%%%%%%%%%%%%
  bond energy constant missing.
  target bond length missing.
  ATOM1: SEGId="D   ",  RESId="79  ",  NAME="C   ",  CHEMical="CX3 "
  ATOM2: SEGId="D   ",  RESId="80  ",  NAME="N   ",  CHEMical="NH1 "
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %CODBON-ERR: missing bond parameters %%%%%%%%%%%%%%%%%%%%%%%%%%
  bond energy constant missing.
  target bond length missing.
  ATOM1: SEGId="N   ",  RESId="79  ",  NAME="C   ",  CHEMical="CX3 "
  ATOM2: SEGId="N   ",  RESId="80  ",  NAME="N   ",  CHEMical="NH1 "
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %CODBON-ERR: program will be aborted.
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 BOMLEV=    0 reached.  Program execution will be terminated.
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 Subroutine DIE called . Terminating


Is it possible to get Xplor to treat this group as an amino acid?
Do I need to do a patch?  (And if so, how?)


        Thanks in advance for any ideas,


Jennifer Ekstrom
Cornell Structural Biology
jennifer at bio.cornell.edu
(607)277-9440