Is this what you mean?
This will match any line which starts with either 'ATOM' or 'HETATM',
followed by any string of arbitrary characters, followed by the string
This indeed works but I do think I need to be a bit more specific.
Lets look again at the line:
ATOM 14 CA GLN A 2 -27.648 -9.581 30.325 1.00 10.00
My goal is to have both the 'ATOM' string and the 'GLN' string colored
Using ^(ATOM|HETATM)\b I can color the ATOM part.
Using \bGLN\b I can color the GLN part.
The problem is that I only want the GLN part to be colored if the line
starts with ATOM. In your reply the complete part starting with ATOM
up to GLN gets colored.