Biophysical characterization of Vpu from HIV‐1 suggests a channel‐pore dualism

Abstract

Vpu from HIV-1 is an 81 amino acid type I integral membrane protein which consists of a cytoplasmic and a transmembrane (TM) domain. The TM domain is known to alter membrane permeability for ions and substrates when inserted into artificial membranes. Peptides corresponding to the TM domain of Vpu (Vpu(1-32)) and mutant peptides (Vpu(1-32)-W23L, Vpu(1-32)-R31V, Vpu(1-32)-S24L) have been synthesized and reconstituted into artificial lipid bilayers. All peptides show channel activity with a main conductance level of around 20 pS. Vpu(1-32)-W23L has a considerable flickering pattern in the recordings and longer open times than Vpu(1-32). Whilst recordings for Vpu(1-32)-R31V are almost indistinguishable from those of the WT peptide, recordings for Vpu(1-32)-S24L do not exhibit any noticeable channel activity. Recordings of WT peptide and Vpu(1-32)-W23L indicate Michaelis-Menten behavior when the salt concentration is increased. Both peptide channels follow the Eisenman series I, indicative for a weak ion channel with almost pore like characteristics.

Oligomerization state and supramolecular structure of the HIV‐1 Vpu protein transmembrane segment in phospholipid bilayers

“…Comparable stability for structurally diverse oligomers in bilayers may explain experimental observations of multiple conductance levels for Vpu ion channels. 1,10,[13][14][15] Given that a variety of Vpu 1-40 oligomer structures coexist in DOPC/DOPG bilayers, we can not analyze our solid-state NMR data unequivocally in terms of a single structure. However, the fact that 2D 13 C-13 C spectra of Vpu in bilayers show a single set of 13 C chemical shifts 17 suggests that peptide conformations and intermolecular interactions in the predominant oligomers are similar.…”

“…9 The second function depends principally on the single transmembrane TM segment of Vpu, contained within residues 1-30, as sequence alterations in the TM segment have been shown to interfere with this function. 2 Full-length Vpu and various N-terminal peptides containing the TM segment have been shown to form cation-selective channels in model membranes 1,[10][11][12][13][14][15] and in cells. 12 These ion channels presumably form by association of a-helical TM segments into homo-oligomeric bundles, with ions passing through the central pore of the helix bundle.…”

Assembly of Viral Membrane Proteins

“…The models 2 and 3 would represent alternative conducting states, which would be in good agreement with the experimental finding of multiple conductance states for Vpu. [51][52][53] More than just one model could contribute to the functioning of Vpu. The results further underline the flexibility of the TM part of the protein.…”

Novel Acylguanidine-Based Inhibitor of HIV-1

“…Most notably, Vpu augments virion release by downregulating CD4 (12-15), whose presence on the cell surface would otherwise promote elimination of infected cells through antibody-dependent cellular cytotoxicity (16-18), as well as the host restriction factor tetherin (also known as BST2 or CD317), whose presence would otherwise capture mature virions at the cell surface (19)(20)(21)(22). Vpu is also reported to form cationselective ion channels (11,(23)(24)(25)(26)(27)(28)(29)(30); however, this property is controversial (31, 32), and its role in HIV-1 replication is unknown (11). Since acylguanidines can also act on host ion channels, host transporters, and viral polymerases (4, 8), additional antiviral mechanisms are possible.…”