Entamoeba histolyticaEhGEF1 structure and mutational analysis: New specific residues critical for function

EhFP10: A FYVE family GEF interacts with myosin IB to regulate cytoskeletal dynamics during endocytosis in Entamoeba histolytica

Motility and phagocytosis are key processes that are involved in invasive amoebiasis disease caused by intestinal parasite Entamoeba histolytica. Previous studies have reported unconventional myosins to play significant role in membrane based motility as well as endocytic processes. EhMyosin IB is the only unconventional myosin present in E. histolytica, is thought to be involved in both of these processes. Here, we report an interaction between the SH3 domain of EhMyosin IB and c-terminal domain of EhFP10, a Rho guanine nucleotide exchange factor. EhFP10 was found to be confined to Entamoeba species only, and to contain a c-terminal domain that binds and bundles actin filaments. EhFP10 was observed to localize in the membrane ruffles, phagocytic and macropinocytic cups of E. histolytica trophozoites. It was also found in early pinosomes but not early phagosomes. A crystal structure of the c-terminal SH3 domain of EhMyosin IB (EhMySH3) in complex with an EhFP10 peptide and co-localization studies established the interaction of EhMySH3 with EhFP10. This interaction was shown to lead to inhibition of actin bundling activity and to thereby regulate actin dynamics during endocytosis. We hypothesize that unique domain architecture of EhFP10 might be compensating the absence of Wasp and related proteins in Entamoeba, which are known partners of myosin SH3 domains in other eukaryotes. Our findings also highlights the role of actin bundling during endocytosis.

G protein signaling in the parasite Entamoeba histolytica

The parasite Entamoeba histolytica causes amebic colitis and systemic amebiasis. Among the known amebic factors contributing to pathogenesis are signaling pathways involving heterotrimeric and Ras superfamily G proteins. Here, we review the current knowledge of the roles of heterotrimeric G protein subunits, Ras, Rho and Rab GTPase families in E. histolytica pathogenesis, as well as of their downstream signaling effectors and nucleotide cycle regulators. Heterotrimeric G protein signaling likely modulates amebic motility and attachment to and killing of host cells, in part through activation of an RGS-RhoGEF (regulator of G protein signaling-Rho guanine nucleotide exchange factor) effector. Rho family GTPases, as well as RhoGEFs and Rho effectors (formins and p21-activated kinases) regulate the dynamic actin cytoskeleton of E. histolytica and associated pathogenesis-related cellular processes, such as migration, invasion, phagocytosis and evasion of the host immune response by surface receptor capping. A remarkably large family of 91 Rab GTPases has multiple roles in a complex amebic vesicular trafficking system required for phagocytosis and pinocytosis and secretion of known virulence factors, such as amebapores and cysteine proteases. Although much remains to be discovered, recent studies of G protein signaling in E. histolytica have enhanced our understanding of parasitic pathogenesis and have also highlighted possible targets for pharmacological manipulation.

Identification and evaluation of inhibitors of the EhGEF1 protein from Entamoeba histolytica

The Dbl family of guanine nucleotide exchange factors (GEFs) is made up of a vast array of members that participate in the activation of the Rho family of small GTPases. Dbl-family proteins promote the exchange of guanosine diphosphate/guanosine triphosphate (GDP/GTP) in their target molecules, resulting in the activation of a variety of signaling pathways involved in diverse cellular events, such as actin-cytoskeleton remodeling, cellular invasion, cell movement, and other functions. It has been reported that members of the Dbl family have important roles in several cellular events in Entamoeba histolytica. These include activation of the actin cytoskeleton, cytokinesis, capping, uroid formation, cellular proliferation, erythrophagocytosis, cell migration, and chemotaxis. Here, we report the identification and testing of inhibitors of the E. histolytica guanine nucleotide exchange factor 1 (EhGEF1) protein (the research compounds 2BYRF, 2BY05, 2BYT6, 2BYLX, and 2BYPD), which decreased the in vitro ability of the protein to exchange GDP/GTP at its target GTPases, EhRacG and EhRho1, by 14.9-85.2%. Interestingly, the drug 1,1'-(1,2-phenylene)-bis-(1H-pyrrole-2,5-dione), which completely inhibits the GEF activity of the Trio protein in human cells, decreases the GEF activity of the EhGEF1 protein on the EhRacG and EhRho1 GTPases by 55.7% and 3.2%, respectively. The identification and evaluation of such inhibitors opens up the possibility of obtaining a new pharmacological tool to study the function of amoeba GEF proteins, their roles in various Rho GTPase-mediated signaling pathways, and the repercussions of modulating their activities with respect to several mechanisms related to E. histolytica pathogenesis.