def get_alignment_pdb_id(alignment):
    """
    Returns a string of the four letter PDB ID found in alignment
    :param alignment:
    :return: 'pdb id'
    """
    pdb_chain_id = alignment.hit_def.encode('ascii').split()[0]
    pdb_id = pdb_chain_id.split('_')[0].lower()
    return pdb_id