Extract the sequences from the PDB file, perform the alignment,
        and load the coordinates of the CA of the common residues.

def _load_data_alignment(self, chain1, chain2):
        """
        Extract the sequences from the PDB file, perform the alignment,
        and load the coordinates of the CA of the common residues.
        """
        parser = PDB.PDBParser(QUIET=True)
        ppb = PDB.PPBuilder()

        structure1 = parser.get_structure(chain1, self.pdb1)
        structure2 = parser.get_structure(chain2, self.pdb2)

        seq1 = str(ppb.build_peptides(structure1)[0].get_sequence())
        seq2 = str(ppb.build_peptides(structure2)[0].get_sequence())

        # Alignment parameters taken from PconsFold renumbering script.
        align = pairwise2.align.globalms(seq1, seq2, 2, -1, -0.5, -0.1)[0]
        indexes = set(i for i, (s1, s2) in enumerate(zip(align[0], align[1]))
                      if s1 != '-' and s2 != '-')
        coord1 = np.hstack([np.concatenate((r['CA'].get_coord(), (1,)))[:, None]
                            for i, r in enumerate(structure1.get_residues())
                            if i in indexes and 'CA' in r]).astype(DTYPE,
                                                                   copy=False)
        coord2 = np.hstack([np.concatenate((r['CA'].get_coord(), (1,)))[:, None]
                            for i, r in enumerate(structure2.get_residues())
                            if i in indexes and 'CA' in r]).astype(DTYPE,
                                                                   copy=False)

        self.coord1 = coord1
        self.coord2 = coord2
        self.N = len(seq1)