The Toxoplasma gondii protein MIC3 requires pro-peptide cleavage and dimerization to function as adhesin

Cérède, Odile; Dubremetz, Jean François; Bout, Daniel; Lebrun, Maryse

doi:10.1093/emboj/21.11.2526

Cited by 74 publications

(66 citation statements)

References 26 publications

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“…The majority of micronemal proteins characterized to date form complexes that are important for proper cellular trafficking and secretion (13,23,24,26). For example, soluble microneme proteins such as MIC1 and MIC4 require interaction with the membrane bound protein MIC6 to ensure proper targeting to the micronemes (24).…”

Section: Discussionmentioning

confidence: 99%

The Toxoplasma Proteins MIC2 and M2AP Form a Hexameric Complex Necessary for Intracellular Survival

Jewett

Sibley

2004

Journal of Biological Chemistry

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Toxoplasma gondii parasites gain entry into host cells through a process that depends on apically stored adhesins that are strategically released during invasion. One of these adhesins, microneme protein 2 (MIC2), is a type one transmembrane protein that binds to an accessory protein known as MIC2-associated protein (M2AP). Together the MIC2⅐M2AP complex participates in host cell attachment and invasion. The short cytoplasmic Cdomain of MIC2 is implicated in protein trafficking and mediating an association with the parasite cytoskeleton. To define the role of the cytoplasmic domain of MIC2, proteins lacking the C-domain were expressed in transgenic T. gondii. Surprisingly, protein trafficking and secretion were not affected. We hypothesized that mutant mic2 lacking the C-domain might be escorted to the micronemes by association with endogenous wild-type MIC2 possessing functional transmembrane and cytoplasmic domains. To investigate this interaction, native blue gels and gel filtration were employed to identify a stable macromolecular MIC2⅐M2AP complex of ϳ450 kDa. Our findings reveal that MIC2 and M2AP proteins form stable hexamers consisting of three ␣␤ dimers. Resolution of this complex has implications for how MIC2⅐M2AP associates with host cell receptors and the cytoskeleton to facilitate parasite motility and invasion.Apicomplexan parasites actively gain entry into host cells by a unique mechanism that depends on the cohesive interaction of cytoskeletal proteins and surface adhesins (1). Host cell invasion is fundamental to diseases caused by this phylum of pathogenic organisms that includes Plasmodium falciparum, the etiological agent of severe malaria and Toxoplasma gondii, the causative agent of toxoplasmosis. Tachyzoites (Toxoplasma) and sporozoites (Plasmodium) employ similar adhesins for active entry into host cells. These adhesins define a family of thrombospondin-related anonymous proteins (TRAPs) 1 (2, 3). TRAP family members are type 1 transmembrane proteins that are comprised of adhesive N-terminal domains that harbor integrin-like A-domains and at least one thrombospondin like domain and a short C-terminal cytoplasmic domain (C-domain) (2, 3). Toxoplasma gondii contains a single TRAP family member called MIC2, which is expressed by all of the invasive stages of the parasite. MIC2 is stored in the apically located microneme secretory organelles. Following host cell contact, microneme vesicles fuse with the proximal plasma membrane depositing MIC2 on the surface of the parasite (4 -6). Images of T. gondii captured at various stages of invasion indicate that MIC2 is translocated to the posterior end of the parasite during the rapid process of entry (7). Ultimately, MIC2 is removed from the parasite surface by a protease that cleaves the MIC2 protein within the transmembrane domain (8, 9). Amino acids within and just external to the transmembrane domain are implicated in this processing event (9, 10). Recently, a Drosophila rhomboid protease was found to cleave a chimeric substrate containing the M...

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Section: Discussionmentioning

confidence: 99%

The Toxoplasma Proteins MIC2 and M2AP Form a Hexameric Complex Necessary for Intracellular Survival

Jewett

Sibley

2004

Journal of Biological Chemistry

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“…Although more than one-half of the known microneme proteins are processed by removal of an Nterminal or internal propeptide, little is known about the functions of these transient elements in the Apicomplexa (Brydges et al, 2000;Donahue et al, 2000;Cerede et al, 2001;Miller et al, 2001;Rabenau et al, 2001;Reiss et al, 2001;Harper et al, 2004b showed that the propeptide of TgMIC3 plays a regulatory role in masking lectin activity (Cerede et al, 2002), additional functions for protein maturation remain untested. The lack of sequence conservation among microneme propeptides suggests that they may fulfill additional roles beyond masking adhesion.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…As a member of the phylum Apicomplexa, T. gondii features a distinct apical complex consisting of three types of secretory organelles. Regulated secretion of proteins from the apical micronemes is required for host cell invasion by providing adhesive protein complexes that bind receptors on the host cell surface (Fourmaux et al, 1996;Cerede et al, 2002;Harper et al, 2004a).Similar to regulated secretory proteins in eukaryotes and in other apicomplexan parasites, several Toxoplasma adhesive protein complexes undergo proteolytic maturation while trafficking to the micronemes (Rabenau et al, 2001;Cerede et al, 2002;Binder and Kim, 2004;Dowse and Soldati, 2004). Although more than one-half of the known microneme proteins are processed by removal of an Nterminal or internal propeptide, little is known about the functions of these transient elements in the Apicomplexa (Brydges et al, 2000;Donahue et al, 2000;Cerede et al, 2001;Miller et al, 2001;Rabenau et al, 2001;Reiss et al, 2001;Harper et al, 2004b showed that the propeptide of TgMIC3 plays a regulatory role in masking lectin activity (Cerede et al, 2002), additional functions for protein maturation remain untested.…”

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confidence: 99%

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A Cleavable Propeptide InfluencesToxoplasmaInfection by Facilitating the Trafficking and Secretion of the TgMIC2–M2AP Invasion Complex

Harper

Huynh

Coppens

et al. 2006

MBoC

102

150

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Propeptides regulate protein function and trafficking in many eukaryotic systems and have emerged as important features of regulated secretory proteins in parasites of the phylum Apicomplexa. Regulated protein secretion from micronemes and host cell invasion are inextricably linked and essential processes for the apicomplexan parasite Toxoplasma gondii. TgM2AP is a propeptide-containing microneme protein found in a heterohexameric complex with the microneme protein TgMIC2, a protein that has a demonstrated fundamental role in gliding motility and invasion. TgM2AP function is also central to these processes, because disruption of TgM2AP (m2apKO) results in secretory retention of TgMIC2, leading to reduced TgMIC2 secretion from the micronemes and impaired invasion. Because the TgM2AP propeptide is predicted to be processed in an intracellular site near where TgMIC2 is retained in m2apKO parasites, we hypothesized that the propeptide and its proteolytic removal influence trafficking and secretion of the complex. We found that proTgM2AP traffics through endosomal compartments and that deletion of the propeptide leads to defective trafficking of the complex within or near this site, resulting in aberrant processing and decreased secretion of TgMIC2, impaired invasion, and reduced virulence in vivo, mirroring the phenotypes observed in m2apKO parasites. In contrast, mutation of several cleavage site residues resulted in normal localization, but it affected the stability and secretion of the complex from the micronemes. Therefore, the propeptide and its cleavage site influence distinct aspects of TgMIC2-M2AP function, with both impacting the outcome of infection. INTRODUCTIONEukaryotic secretory proteins use an assortment of luminal or cytoplasmic forward targeting signals to navigate the secretory system for eventual delivery to the extracellular environment. Among the least well understood of the luminal signals are cleavable elements known as propeptides, which are typically positioned either internally or, more commonly, at the N terminus of a protein. Propeptides have been shown to serve in several capacities. They can facilitate the folding of their cognate protein, regulate its activity or oligomeric assembly, or direct it to a particular intracellular compartment within the endolysosomal or secretory system. For proproteins destined for the regulated secretory pathway, proteolytic processing (also termed proteolytic maturation) typically accompanies the condensation of immature secretory granule contents (Orci et al., 1987;Kuiper and Martens, 2000). Yet, the precise role of proteolytic maturation in the biogenesis and discharge of regulated secretory organelles remains contentious (Arvan and Halban, 2004).Toxoplasma gondii, the etiological agent of toxoplasmosis, is a genetically tractable protozoan parasite that causes widespread infection in humans resulting in significant economic losses worldwide (Jones et al., 2001). As a member of the phylum Apicomplexa, T. gondii features a distinct apical complex consis...

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“…As an important member of the MIC family, MIC8 participates in T. gondii invasion through interaction with soluble MIC3 (Cérède et al, 2002;Kessler et al, 2008), and is a potential vaccine candidate against acute and chronic T. gondii infections in a mouse model (Liu et al, 2010;Li et al, 2014). To investigate the genetic diversity of the MIC8 gene, 16 T. gondii strains from different hosts and geographical locations, and two reference isolates were examined in this study.…”

Section: Introductionmentioning

confidence: 99%

Nucleotide variation in the Toxoplasma gondii micronemal protein 8 gene

Song

Wang

et al. 2016

Genet. Mol. Res.

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ABSTRACT. Toxoplasma gondii is a successful opportunistic protozoan distributed worldwide, which can infect all vertebrates, leading to serious infection, blindness, and abortion. Micronemal (MIC) proteins are critically important for T. gondii infection, as they participate in various stages of the Toxoplasma life cycle, including invasion and attachment to host cells. MIC8 secretion relies on the concentration of intracellular calcium, and can mediate the invasion of T. gondii by interacting with soluble MIC3. To investigate genetic diversity of the MIC8 gene, 16 T. gondii strains from different hosts and geographical locations, and two reference isolates (ToxoDB: TGME49_245490 and TGVEG_245490) were examined in this study. The results showed that all the examined MIC8 genes are 2055 bp, with an A+T content ranging from 50.2 to 50.6%. Conversely, lower levels of variation were detected within their nucleotide and amino acid sequences. Phylogenetic analyses indicated that three classical genotypes of T. gondii and the ToxoDB#9 genotype did not group exclusively via Bayesian inference, maximum parsimony, neighbor joining, and/or maximum likelihood assays based on the nucleotide and amino acid sequences of the MIC8 gene. In summary, the T. gondii MIC8 gene is not a suitable marker for population genetic studies of this parasite.

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The Toxoplasma gondii protein MIC3 requires pro-peptide cleavage and dimerization to function as adhesin

Cited by 74 publications

References 26 publications

The Toxoplasma Proteins MIC2 and M2AP Form a Hexameric Complex Necessary for Intracellular Survival

The Toxoplasma Proteins MIC2 and M2AP Form a Hexameric Complex Necessary for Intracellular Survival

A Cleavable Propeptide InfluencesToxoplasmaInfection by Facilitating the Trafficking and Secretion of the TgMIC2–M2AP Invasion Complex

Nucleotide variation in the Toxoplasma gondii micronemal protein 8 gene

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