Figure 5.

Purfalcamine and SE5 P2 peptide block protease activity. A, i, a synthetic fluorescent peptide substrate, LLVY-AMC, was added to P. falciparum cultures at early schizont stage, and its hydrolysis was visualized by blue fluorescence. DIC, differential interference contrast. ii, the fluorescence signal was inhibited by addition of the PfSERA5 inhibitory peptide SE5 P2 (500 μm), and this change was quantified spectrophotometrically. B, i and ii, hydrolysis of the synthetic substrate peptide was also inhibited by purfalcamine, a known inhibitor of PfCDPK1. This inhibition was captured and quantified using confocal microscopy. Together, these results indicate possible regulation of PfSERA5 activity by phosphorylation.