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An ion-channel forming protein produced by Entamoeba histolytica
Abstract:
We have identified a remarkable ion-channel forming material in virulent strains of Entamoeba histolytica that may be responsible for many of the symptoms associated with amoebic dysentery. A polypeptide that we refer to as amoebapore is shed into the growth media and is also found within the amoeba in a high speed sedimentable fraction. Amoebapore has the distinctive property of spontaneously incorporating into lipid bilayers, liposomes, and cells, leading to progressive and irreversible changes in the ion conductance of the target membranes. Exposure of planar lipid bilayers to amoebapore -containing fractions under voltage clamp conditions results in an almost immediate and progressive incorporation of ion channels which continues in an irreversible manner leading to a fall in membrane impedance of up to five orders of magnitude. The ion-channel conductance is moderately cation-selective, voltage dependent, and displays a unit size of 1.6 +/- 0.2 nanoSiemens in 1 M KCl at -10 mV. In the bilayer, the amoebapore -induced conductance exhibits an in situ sensitivity to protease. Amoebapore is mainly concentrated in a fraction sedimenting at 150 000 g. It is insoluble in Triton X-100 but can be dissociated in an active state in 1% SDS. Under these conditions it has an apparent mol. wt. of 13 000 daltons.
Insights
Researchers discovered amoebapore, an ion-channel forming protein in virulent Entamoeba histolytica, which causes irreversible changes in cell membranes and may explain amoebic dysentery symptoms.
Area of Science:
- Molecular biology
- Biophysics
- Parasitology
Background:
- Virulent Entamoeba histolytica causes amoebic dysentery.
- The molecular mechanisms underlying amoebic dysentery pathogenesis are not fully understood.
Purpose of the Study:
- To identify and characterize the ion-channel forming material responsible for Entamoeba histolytica virulence.
- To investigate the properties and function of this material in biological membranes.
Main Methods:
- Isolation and purification of amoebapore from Entamoeba histolytica.
- Incorporation of amoebapore into artificial lipid bilayers and liposomes.
- Electrophysiological measurements (voltage clamp) to assess ion channel activity.
- Protease sensitivity assays and SDS-PAGE for molecular weight determination.
Main Results:
- Identified amoebapore, a polypeptide shed by virulent Entamoeba histolytica.
- Amoebapore spontaneously incorporates into lipid bilayers, liposomes, and cells, altering ion conductance.
- Induced ion channels are cation-selective, voltage-dependent, and exhibit a unit conductance of 1.6 ± 0.2 nS in 1 M KCl.
- Amoebapore is protease-sensitive in situ and has an apparent molecular weight of 13,000 daltons.
Conclusions:
- Amoebapore is a key virulence factor in Entamoeba histolytica.
- Its ion-channel forming activity disrupts membrane integrity, contributing to amoebic dysentery pathology.
- Further research into amoebapore could lead to novel therapeutic strategies against amoebiasis.