Two different PSG1 mutants were generated. We mutated two residues at positions 93 and 95 within the N-domain of PSG1 to generate PSG1GDD!SDL-FC and three amino acids in positions 64, 70, and 77 to generate PSG1RNN!AAA-FC (see Fig. 6A, lanes 2 and 3, respectively) . The level of purity achieved after protein A purification of all proteins was more than 90%.