Residues 55 and 269 in VP1 protein play very important role in hemagglutination of RBCs by Viral Like Particles (VLPs).

Hemagglutination was conducted as described in Materials and Methods using serial dilutions of VLPs starting from 200 µg/ml. VLPs were added to type O RBC and incubated at 4°C for 3 hours. Agglutination is visualized by the lack of a round pellet formed by the settling of RBCs out of suspension. F55 is a VP1 variant with phenylalanine at the position 55 (AAT09831), F269 is a VP1 variant with phenylalanine at the position 269 (BAE0011). WT (AAQ88264) and Mad-1 (P03089) are VP1 variants with leucine and serine at positions 55 and 269 respectively.