Biopython PDB: calculate distance between an atom and a point
<p>Using a typical pdb file, I am able to calculate the distance between two atoms in a structure using a method similar to that presented in the Biopython documentation.  Shown here:</p>

<pre><code>from Bio import PDB
parser = PDB.PDBParser()

pdb1 ='./4twu.pdb' 
structure = parser.get_structure("4twu", pdb1) 
model = structure[0] 
chain = model['A'] 
residue1 = chain[1] 
residue2 = chain[2]
atom1 = residue1['CA'] 
atom2 = residue2['CA'] 

distance = atom1-atom2 

print(distance)
</code></pre>

<p>Is there a method within Biopython to calculate the distance from an atom to a fixed point with xyz coordinates?  If not Biopython, what would be the best method to solve this problem?  Thanks.</p>