Many human pathogens use host cell-surface receptors to attach and invade cells. Often, the
host-pathogen interaction affinity is low, presenting opportunities to block invasion using a
soluble, high-affinity mimic of the host protein. The Plasmodium falciparum reticulocyte-binding
protein homolog 5 (RH5) provides an exciting candidate for mimicry: it is highly conserved and
its moderate affinity binding to the human receptor basigin (KD≥1 μM) is an essential step in
erythrocyte invasion by this malaria parasite. We used deep mutational scanning of a soluble
fragment of human basigin to systematically characterize point mutations that enhance basigin
affinity for RH5 and then used Rosetta to design a variant within the sequence space of
affinity-enhancing mutations. The resulting seven-mutation design exhibited 2,500-fold higher
affinity (KD<1 nM) for RH5 with a very slow binding off rate (0.23 h-1) and reduced the effective
Plasmodium growth-inhibitory concentration by at least tenfold compared to human basigin. The
design provides a favorable starting point for engineering on-rate improvements that are likely
to be essential to reach therapeutically effective growth inhibition. Designed mimics may provide
therapeutic advantages over antibodies, since the mimics bind to essential surfaces on the target
pathogen proteins, reducing the likelihood for the emergence of escape mutants