/usr/share/massxpert/pol-chem-defs/protein-1-letter/pdb-code-conversion.dic is in massxpert-data 3.4.1-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | # Converts from code on the left of '>' to code on the right.
# Number of letters allowed in each code is
# described with syntax 1>3 and that line should be the first
# non-comment line in this file.
3>1
ALA>A
CYS>C
ASP>D
GLU>E
PHE>F
GLY>G
HIS>H
ILE>I
LYS>K
LEU>L
MET>M
ASN>N
PRO>P
GLN>Q
ARG>R
SER>S
THR>T
VAL>V
TRP>W
TYR>Y
|