How can single-digit values from an array be used to replace the B-factor 5-digit values in a PDB file?

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To replace the B-factor 5-digit values in a PDB file with single-digit values from an array, you can use a programming language or script that supports file input/output and string manipulation. Here are steps you can follow:

1. Load the PDB file into memory as a string or list of strings.
2. Read the single-digit values from the array into a list.
3. Loop through each line of the PDB file string or list and parse out the B-factor value (which is located in columns 61-66 of each ATOM or HETATM line).
4. Replace the B-factor value in the line with a single-digit value from the array, using the same column formatting.
5. Write the modified PDB file string or list back to disk.

Here's some sample Python code that demonstrates the approach:

# Load PDB file into memory
with open('protein.pdb', 'r') as f:
    pdb_lines = f.readlines()

# Define array of single-digit values
bfactors = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0]

# Loop through each line of PDB file and replace B-factor value
for i, line in enumerate(pdb_lines):
    if line.startswith(('ATOM', 'HETATM')):
        bfactor = float(line[60:66].strip())
        new_bfactor = bfactors[i % len(bfactors)]
        pdb_lines[i] = line[:60] + '{:6.2f}'.format(new_bfactor) + line[66:]

# Write modified PDB file to disk
with open('protein_modified.pdb', 'w') as f:
    f.writelines(pdb_lines)

In this example, the code reads in the PDB file protein.pdb and assumes that every ATOM or HETATM line contains a B-factor value. It also uses a simple cycle to select a single-digit value from the bfactors array for each line of the PDB file. Finally, it writes the modified PDB file as protein_modified.pdb.