    New chain ID            Original chain ID

6x6l-pdb-bundle1.pdb:
           A                        AX
           B                        BX
           C                        CX
           D                        DX
           E                        EX
           F                        FX
           G                        GX
           H                        HX
           I                        IX
           J                        JX
           K                        KX
           L                        LX
           M                        MX
           N                        NX
           O                        OX
           P                        PX
           Q                        QX
           R                        AY
           S                        BY
           T                        CY
           U                        DY
           V                        EY
           W                        FY
           X                        GY
           Y                        HY
           Z                        IY
           a                        JY
           b                        KY
           c                        LY
           d                        MY
           e                        NY
           f                        OY
           g                        PY
           h                        QY
