Human immunodeficiency virus 1 Vpu protein does not affect the conversion of influenza A virus hemagglutinin to its low-pH conformation in an acidic trans-Golgi compartment.

The 81-aa Vpu protein of Human immunodeficiency virus 1 (HIV-1) is a structural analogue of the M2 protein of influenza A virus (IAV). Expression of Vpu in Xenopus oocytes has showed that it can form a voltage-activated ion channel permeable to Na+ and K+ ions (Ewart et al., 1996). To investigate whether Vpu has a pH-modulating activity comparable to that of M2, Vpu was co-expressed with the pH-sensitive hemagglutinin (HA) from IAV. The results indicated that Vpu was unable to reduce the acidity of the exocytic pathway and reduce the conversion of the pH-sensitive HA to its low-pH conformation during transport to the cell surface. Despite these findings, we did not exclude the possibility that Vpu formed a weak ion channel with almost pore-like characteristics as was recently suggested.