Apical membrane antigen 1 (AMA1) plays an essential role in host cell invasion by apicomplexan parasites. A recent study by Collins et al. investigated the mode of action of an anti-AMA1 invasion-inhibitory antibody. They demonstrated the interference of this antibody with invasion complex formation, which was dependent in turn on a single conserved tyrosine residue in AMA1. Their findings reveal important new insights into parasite biology and are highly relevant for rational vaccine design.