[BioPython] protein-ligand interactions

[mitlox]

Hello,
I have a solved structure (1E8W) with a ligand and I would like to know 
which residues are within 3A of the ligand. This 3A is a cut off and 
should be using just for the C-alpha in each residue, but it would be 
great if I know which C-alpha belongs to a residue.

I am newbie in Biopython/Python, maybe anyone know an example how is it 
possible?

Thank you in advance.

Best regards