How to extract residues from specific chain of interest from multiple pdb files?

Question

I'm new to biopython & I'm trying to extract residues from specific chain of each file from a list of 316 pdb files. Eg: 1d8t has four chains A, B, C & D of which my interest is to extract just the residues of C chain. As the chain of interest differs for different files, I'm not knowing how to extract specific chain residue from each file and save it separately.

from Bio import *
from Bio.PDB.PDBParser import PDBParser
from Bio.PDB.Polypeptide import PPBuilder
structure = PDBParser().get_structure('1d8t', '1d8t.pdb')    


model = structure[0]
chain = model['C']

for i in chain.get_residues():
    print(i)

With the above code I was able to extract the residues of C chains not sure how to proceed for multiple files in python.

Answer 1

Create a function and run it for each pdb file.

from Bio.PDB import PDBParser

def print_residues(name, pdb_file, chain_key, out_file):
    parser = PDBParser()
    structure = parser.get_structure(name, pdb_file)
    model = structure[0]
    chain = model[chain_key]
    with open(out_file, 'w') as fp:
        for i in chain.get_residues():
            print(i, file=fp)

Then run the function for all pdb files.

print_residues('1d8t', '1d8t.pdb', 'C', '1d8t.txt')
# ...