Guanylyl Cyclase Activity Associated with Putative Bifunctional Integral Membrane Proteins in Plasmodium falciparum

Abstract

We report here that guanylyl cyclase activity is associated with two large integral membrane proteins (PfGC␣ and PfGC␤) in the human malaria parasite Plasmodium falciparum. Unusually, the proteins appear to be bifunctional; their amino-terminal regions have strong similarity with P-type ATPases, and the sequence and structure of the carboxyl-terminal regions conform to that of G protein-dependent adenylyl cyclases, with two sets of six transmembrane sequences, each followed by a catalytic domain (C1 and C2). However, amino acids that are enzymatically important and present in the C2 domain of mammalian adenylyl cyclases are located in the C1 domain of the P. falciparum proteins and vice versa. In addition, certain key residues in these domains are more characteristic of guanylyl cyclases. Consistent with this, guanylyl cyclase activity was obtained following expression of the catalytic domains of PfGC␤ in Escherichia coli. In P. falciparum, expression of both genes was detectable in the sexual but not the asexual blood stages of the life cycle, and PfGC␣ was localized to the parasite/parasitophorous vacuole membrane region of gametocytes. The profound structural differences identified between mammalian and parasite guanylyl cyclases suggest that aspects of this signaling pathway may be mechanistically distinct.

The development of malaria parasites in the mosquito midgut

“…In P . falciparum , two integral guanylyl cyclases have been identified, GCα and GCβ (Carucci et al ., 2000). While GCα was refractory to deletion in both P .…”

GTPγS Regulation of a 12-Transmembrane Guanylyl Cyclase Is Retained after Mutation to an Adenylyl Cyclase

“…This hypothesis has been supported experimentally, because mutant GCs without this glutamate have no GC activity (47,48). This glutamate is also present in evolutionary distant GCs, such as GCs from Paramecium, Plasmodium (14,15), and Dictyostelium GCA (13), which most likely have evolved from ACs independently from the traditional GCs. In ACs the counterpart of this glutamate is a lysine (Lys-938 in ACII) that interacts with the N-1 of the P-site inhibitor 2Ј-deoxy-3Ј-AMP in the x-ray structure (1).…”

“…In Paramecium, Tetrahymena, and Plasmodium, GCs with the same topology have been found, but at the N terminus these proteins contain a P-type ATPase, providing an additional 10 membrane-spanning region (14,15). The regulation of GC in these last three organisms is essentially unknown.…”

Phospholipases during membrane dynamics in malaria parasites

“…Once in the mosquito midgut, the intraerythrocytic gametocytes sense the change of hosts due to the perception of environmental factors present in the gut lumen, triggering their egress from the RBC and their transformation into gametes. Initially, a plasmodial guanylyl cyclase becomes activated, leading to the synthesis of cyclic GMP (cGMP) (Carucci et al, 2000;Muhia et al, 2001). The rise of cGMP activates the cGMP-dependent protein kinase G, which regulates the generation of PIP 2 (Alam et al, 2015;Brochet et al, 2014;McRobert et al, 2008).…”