    New chain ID            Original chain ID

7b6u-pdb-bundle1.pdb:
           A                       AAA
           B                       BBB
           C                       CCC
           D                       DDD
           E                       EEE
           F                       FFF
           G                       GGG
           H                       HHH
           I                       III
           J                       JJJ
           K                       AaA
           L                       AdA
           M                       BbB
           N                       CaC
           O                       DaD
           P                       DdD
           Q                       EaE
           R                       FaF
           S                       FdF
           T                       GaG
           U                       HaH
           V                       HdH
           W                       IaI
           X                       JaJ
           Y                       JdJ
