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The Vpu protein of human immunodeficiency virus type 1 forms cation-selective ion channels
G D Ewart1, T Sutherland, P W Gage
1John Curtin School of Medical Research, Australian National University, Canberra City, Australian Capital Territory.
Abstract:
Vpu is a small phosphorylated integral membrane protein encoded by the human immunodeficiency virus type 1 genome and found in the endoplasmic reticulum and Golgi membranes of infected cells. It has been linked to roles in virus particle budding and degradation of CD4 in the endoplasmic reticulum. However, the molecular mechanisms employed by Vpu in performance of these functions are unknown. Structural similarities between Vpu and the M2 protein of influenza A virus have raised the question of whether the two proteins are functionally analogous: M2 has been demonstrated to form cation-selective ion channels in phospholipid membranes. In this paper we provide evidence that Vpu, purified after expression in Escherichia coli, also forms ion channels in planar lipid bilayers. The channels are approximately five- to sixfold more permeable to sodium and potassium cations than to chloride or phosphate anions. A bacterial cross-feeding assay was used to demonstrate that Vpu can also form sodium-permeable channels in vivo in the E. coli plasma membrane.
Insights
The human immunodeficiency virus type 1 Vpu protein forms ion channels in cell membranes. This finding suggests a novel mechanism for viral function and potential therapeutic targets.
Area of Science:
- Virology
- Molecular Biology
- Biophysics
Background:
- The Vpu protein from human immunodeficiency virus type 1 (HIV-1) is involved in viral budding and CD4 degradation.
- The precise molecular mechanisms of Vpu's functions remain unclear.
- Structural similarities exist between HIV-1 Vpu and influenza A virus M2 protein, suggesting potential functional analogy, particularly ion channel formation.
Purpose of the Study:
- To investigate whether the HIV-1 Vpu protein possesses ion channel activity.
- To explore the ion selectivity and in vivo functionality of Vpu-mediated channels.
Main Methods:
- Purification of Vpu protein expressed in Escherichia coli.
- Reconstitution of purified Vpu into planar lipid bilayers for electrophysiological measurements.
- Utilizing a bacterial cross-feeding assay to assess Vpu channel function in vivo.
Main Results:
- Purified Vpu forms ion channels in planar lipid bilayers.
- These Vpu-mediated channels exhibit greater permeability to cations (sodium, potassium) than anions (chloride, phosphate).
- Vpu was demonstrated to form functional sodium-permeable channels in the plasma membrane of E. coli in vivo.
Conclusions:
- The HIV-1 Vpu protein functions as an ion channel.
- Vpu-mediated ion channel activity may contribute to its roles in viral replication and pathogenesis.
- This ion channel activity represents a potential target for antiviral therapies.