The malaria parasite egress protease SUB1 is a calcium-dependent redox switch subtilisin.

Chrislaine Withers-Martinez,Guy G Dodson,Evangelos Christodoulou,Lesley F Haire,Michael J Blackman,Philip A Walker,Malcolm Strath,Steven A Howell,Fiona Hackett

doi:10.1038/ncomms4726

Abstract

Malaria is caused by a protozoan parasite that replicates within an intraerythrocytic parasitophorous vacuole. Release (egress) of malaria merozoites from the host erythrocyte is a highly regulated and calcium-dependent event that is critical for disease progression. Minutes before egress, an essential parasite serine protease called SUB1 is discharged into the parasitophorous vacuole, where it proteolytically processes a subset of parasite proteins that play indispensable roles in egress and invasion. Here we report the first crystallographic structure of Plasmodium falciparum SUB1 at 2.25 Å, in complex with its cognate prodomain. The structure highlights the basis of the calcium dependence of SUB1, as well as its unusual requirement for interactions with substrate residues on both prime and non-prime sides of the scissile bond. Importantly, the structure also reveals the presence of a solvent-exposed redox-sensitive disulphide bridge, unique among the subtilisin family, that likely acts as a regulator of protease activity in the parasite.

Highlights

Malaria is caused by a protozoan parasite that replicates within an intraerythrocytic parasitophorous vacuole
Repeated cycles of intraerythrocytic replication and egress lead to a gradually increasing parasitaemia and clinical disease. This varies in severity depending on the Plasmodium species, but in the most virulent form of malaria, caused by Plasmodium falciparum, initial febrile episodes can quickly lead to severe pathology including anaemia, hypoglycaemia, respiratory distress, coma and other complications that are often fatal[1]
Our rPfSUB1cat–Prodp9–Fab structure does not provide a complete picture of the molecular structure of the native mature enzyme

Summary

Introduction

Malaria is caused by a protozoan parasite that replicates within an intraerythrocytic parasitophorous vacuole. Repeated cycles of intraerythrocytic replication and egress lead to a gradually increasing parasitaemia and clinical disease This varies in severity depending on the Plasmodium species, but in the most virulent form of malaria, caused by Plasmodium falciparum, initial febrile episodes can quickly lead to severe pathology including anaemia, hypoglycaemia, respiratory distress, coma and other complications that are often fatal[1]. An additional feature of the cleavage sites is the invariable presence of acidic (Glu, Asp) or hydroxyl-containing (Ser, Thr) residues at one or more of the proximal 50-side positions flanking the scissile bond[8] This observation, together with mutational studies and analysis of synthetic substrates based on these cleavage motifs, has indicated that—unusually for a S8A family subtilisin—substrate recognition by PfSUB1 requires interactions with both prime and non-primeside residues of the cleavage site. The proteolytic activity of the mature enzyme is likely suppressed during storage to prevent autolysis, but it is unknown how this is achieved, or how the protease is activated on release into the PV just before egress

Methods

Results

Conclusion