A Plasmodium cysteine protease required for efficient transition from the liver infection stage

Abstract

The transitions between developmental stages are critical points in the Plasmodium life cycle. The development of Plasmodium in the livers of their mammalian hosts bridges malaria transmission and the onset of clinical symptoms elicited by red blood cell infection. The egress of Plasmodium parasites from the liver must be a carefully orchestrated process to ensure a successful switch to the blood stage of infection. Cysteine protease activity is known to be required for liver-stage Plasmodium egress, but the crucial cysteine protease (s) remained unidentified. Here, we characterize a member of the papain-like cysteine protease family, Plasmodium berghei serine repeat antigen 4 (PbSERA4), that is required for efficient initiation of blood-stage infection. Through the generation PbSERA4-specific antisera and the creation of transgenic parasites expressing fluorescently tagged protein, we show that PbSERA4 is expressed and proteolytically processed in the liver and blood stages of infection. Targeted disruption of PbSERA4 results in viable and virulent blood-stage parasites. However, upon transmission from mosquitoes to mice, Pbsera4(-) parasites displayed a reduced capacity to initiate a new round of asexual blood-stage replication. Our results from cultured cells indicate that this defect results from an inability of the PbSERA4-deficient parasites to egress efficiently from infected cells at the culmination of liver-stage development. Protection against infection with wildtype P. berghei could be generated in animals in which Pbsera4(-) parasites failed to establish infection. Our findings confirm that liver-stage merozoite release is an active process and demonstrate that this parasite-encoded cysteine protease contributes to parasite escape from the liver.

Autocatalytic activation of a malarial egress protease is druggable and requires a protein cofactor

“…SERA6-inhibitory compounds may also prove useful beyond the asexual blood stages of the malaria parasite life cycle. Other members of the SERA multigene family have been implicated in egress of liver-stage merozoites from hepatocytes to establish the erythrocytic cycle (Putrianti et al, 2020), as well as in parasite egress within the mosquito vector (Aly & Matuschewski, 2005), with implications for preventing disease transmission. These orthologues may be similarly susceptible to SERA6 inhibitors.…”

Dissecting Disease Tolerance in Plasmodium vivax Malaria Using the Systemic Degree of Inflammatory Perturbation

“…Despite that, in participants with symptomatic malaria, the degree of CCL2 perturbation exhibited two negative correlations, vs. IL-6 and TNF-α. Moreover, ALT was the top node in the matrix calculated for symptomatic malaria, highlighting the relevance of liver inflammatory reaction in P.vivax infection [46, 47]. Importantly, different from our previous publication using absolute concentration values of inflammatory markers, where we had identified a highest number of correlations in matrices from asymptomatic patients [39], here, by imputing MDP values instead, we found that this group of participants exhibit the lowest network density, suggesting that the absence of symptoms in response to P. vivax is associated with a potential uncoupling of the perturbed inflammatory response, probably due to lack of immune activation in peripheral blood.…”

“…;[44][45][46][47][48][49][50];[39][40][41][42][43][44][45][46][47][48][49][50] years, respectively, P<0.001). No differences were noted in regard to sex distribution (P=0.43).…”

Malaria parasite egress at a glance

“…Both PVM rupture and host membrane cytoskeletal changes that lead to merosome formation are inhibited by E64 ( Burda et al, 2017a ), a peptidyl epoxide selective for cysteine proteases. Importantly, very recent reverse genetic work has implicated the cysteine protease-like PbSERA4 (‘group II’ SERA; see Box 2 ) in liver stage egress ( Putrianti et al, 2020 ). Expression and proteolytic processing of the ‘group III SERA’ (see Box 2 ) PbSERA3 has also been demonstrated in liver stage parasites ( Schmidt-Christensen et al, 2008 ), although in this case its importance in egress was not examined.…”