The zeta potential decreases from around 15 mV to -9 mV with increasing pH values and crosses 0 mV between pH 6 and 6.3, marking the isoelectric point (IEP) of AP205 VLP (see Figure ). Hence, electrostatic repulsion at pH 6.5 is compromised, which triggers the aggregation process into partially geometrically ordered structures that show Bragg reflections in SAXS.