Pepstatin A, a pentapeptide isolated from Streptomyces sp. is a strong inhibitor of aspartyl proteases such as pepsin, cathepsin D, and renin. Pepstatin is active against HIV-1 and Plasmodium falciparum. HIV-infected H9 cells incubated with pepstatin A at 10-4M for 2, 4 or 10 days had significantly reduced HIV core antigen (p24) and no infectious HIV. Pepstatin A exerts its antimalarial activity via P. falciparum plasmepsin II binding sites. Pepstatin A suppresses NF-​κB ligand (RANKL)​-​induced osteoclast differentiation and decreases the expression of nuclear factor of activated T cells c1 (NFATc1)​, suggesting that suppresses the differentiation of osteoclasts through the blockade of ERK signaling and the inhibition of NFATc1 expression.