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Participation of the serine-rich Entamoeba histolytica protein in amebic phagocytosis of apoptotic host cells.

ABSTRACT: Entamoeba histolytica is an intestinal ameba that causes dysentery and liver abscesses. Cytotoxicity and phagocytosis of host cells characterize invasive E. histolytica infection. Prior to phagocytosis of host cells, E. histolytica induces apoptotic host cell death, using a mechanism that requires contact via an amebic galactose-specific lectin. However, lectin inhibition only partially blocks phagocytosis of already dead cells, implicating at least one additional receptor in phagocytosis. To identify receptors for engulfment of apoptotic cells, monoclonal antibodies against E. histolytica membrane antigens were screened for inhibition of phagocytosis. Of 43 antibodies screened, one blocked lectin-independent uptake of apoptotic cells, with >90% inhibition at a dose of 20 microg/ml (P < 0.0003 versus control). The same antibody also inhibited adherence to apoptotic lymphocytes and, to a lesser extent, adherence to and killing of viable lymphocytes. The antigen recognized by the inhibitory antibody was purified by affinity chromatography and identified by liquid chromatography-mass spectrometry as the serine-rich E. histolytica protein (SREHP). Consistent with this, the inhibitory antibody bound to recombinant SREHP present in bacterial lysates on immunoblots. The SREHP is an abundant immunogenic surface protein of unclear function. The results of this unbiased antibody screen strongly implicate the SREHP as a participant in E. histolytica phagocytosis and suggest that it may play an important role in adherence to apoptotic cells.

SUBMITTER: Teixeira JE

PROVIDER: S-EPMC2258814 | biostudies-literature | 2008 Mar

REPOSITORIES: biostudies-literature

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Participation of the serine-rich Entamoeba histolytica protein in amebic phagocytosis of apoptotic host cells.

Teixeira Jose E JE Huston Christopher D CD

Infection and immunity 20071217 3

Entamoeba histolytica is an intestinal ameba that causes dysentery and liver abscesses. Cytotoxicity and phagocytosis of host cells characterize invasive E. histolytica infection. Prior to phagocytosis of host cells, E. histolytica induces apoptotic host cell death, using a mechanism that requires contact via an amebic galactose-specific lectin. However, lectin inhibition only partially blocks phagocytosis of already dead cells, implicating at least one additional receptor in phagocytosis. To id ...[more]

PMID: 18086807

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Project description:BackgroundAmoebiasis is the third most common parasitic cause of morbidity and mortality, particularly in countries with poor hygienic settings. There exists an ambiguity in the diagnosis of amoebiasis, and hence there arises a necessity for a better diagnostic approach. Serine-rich Entamoeba histolyticaprotein (SREHP), peroxiredoxin and Gal/GalNAc lectin are pivotal in E. histolyticavirulence and are extensively studied as diagnostic and vaccine targets. For elucidating the cellular function of these proteins, details regarding their respective quaternary structures are essential. However, studies in this aspect are scant. Hence, this study was carried out to predict the structure of these target proteins and characterize them structurally as well as functionally using appropriate in-silicomethods.MethodsThe amino acid sequences of the proteins were retrieved from National Centre for Biotechnology Information database and aligned using ClustalW. Bioinformatic tools were employed in the secondary structure and tertiary structure prediction. The predicted structure was validated, and final refinement was carried out.ResultsThe protein structures predicted by i-TASSER were found to be more accurate than Phyre2 based on the validation using SAVES server. The prediction suggests SREHP to be an extracellular protein, peroxiredoxin a peripheral membrane protein while Gal/GalNAc lectin was found to be a cell-wall protein. Signal peptides were found in the amino-acid sequences of SREHP and Gal/GalNAc lectin, whereas they were not present in the peroxiredoxin sequence. Gal/GalNAc lectin showed better antigenicity than the other two proteins studied. All the three proteins exhibited similarity in their structures and were mostly composed of loops.DiscussionThe structures of SREHP and peroxiredoxin were predicted successfully, while the structure of Gal/GalNAc lectin could not be predicted as it was a complex protein composed of sub-units. Also, this protein showed less similarity with the available structural homologs. The quaternary structures of SREHP and peroxiredoxin predicted from this study would provide better structural and functional insights into these proteins and may aid in development of newer diagnostic assays or enhancement of the available treatment modalities.

Dataset Information

Participation of the serine-rich Entamoeba histolytica protein in amebic phagocytosis of apoptotic host cells.

Publications

Participation of the serine-rich Entamoeba histolytica protein in amebic phagocytosis of apoptotic host cells.

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