Structures of plasmepsin X from P. falciparum reveal a novel inactivation mechanism of the zymogen and molecular basis for binding of inhibitors in mature enzyme

Plasmodium falciparum plasmepsin X ( Pf PMX), involved in the invasion and egress of this deadliest malarial parasite, is essential for its survival and hence considered as an important drug target. We report the first crystal structure of Pf PMX zymogen containing a novel fold of its prosegment. A unique twisted loop from the prosegment and arginine 244 from the mature enzyme are involved in zymogen inactivation; such mechanism, not previously reported, might be common for apicomplexan proteases similar to Pf PMX. The maturation of Pf PMX zymogen occurs through cleavage of its prosegment at multiple sites. Our data provide thorough insights into the mode of binding of a substrate and a potent inhibitor 49c to Pf PMX. We present molecular details of inactivation, maturation, and inhibition of Pf PMX that should aid in the development of potent inhibitors against pepsin-like aspartic proteases from apicomplexan parasites. ### Competing Interest Statement The authors have declared no competing interest.