Targets of a protease inhibitor, KNI-272, in HIV-1-infected cells

Modulation of HIV-1-host interaction: role of the Vpu accessory protein

Viral protein U (Vpu) is a type 1 membrane-associated accessory protein that is unique to human immunodeficiency virus type 1 (HIV-1) and a subset of related simian immunodeficiency virus (SIV). The Vpu protein encoded by HIV-1 is associated with two primary functions during the viral life cycle. First, it contributes to HIV-1-induced CD4 receptor downregulation by mediating the proteasomal degradation of newly synthesized CD4 molecules in the endoplasmic reticulum (ER). Second, it enhances the release of progeny virions from infected cells by antagonizing Tetherin, an interferon (IFN)-regulated host restriction factor that directly cross-links virions on host cell-surface. This review will mostly focus on recent advances on the role of Vpu in CD4 downregulation and Tetherin antagonism and will discuss how these two functions may have impacted primate immunodeficiency virus cross-species transmission and the emergence of pandemic strain of HIV-1.

Replication-dependent fitness recovery of Human immunodeficiency virus 1 harbouring mutations of Asn17 of the nucleocapsid protein

The genetic stability of attenuated Human immunodeficiency virus 1 (HIV-1) variants harbouring mutations (Gly or Lys) of Asn17, the protease-cleavage site of the proximal zinc finger of the nucleocapsid protein, was studied. All possible codons for the Gly mutants were tested as starting sequences. Long-term replication assays revealed that the mutants were unstable; mutations of Gly17 to Arg, Ala, Ser and Cys, as well as a Lys17Asn reversion, were observed. Replication kinetic assays in H9 cells revealed that the replication of Ala, Ser and Arg mutants was improved substantially compared with the Gly variant; the infectivity of Ala17 and Ser17 viruses was equal to, and that of Arg17 was almost equal to, the infectivity of the wild-type virus. Kinetic analysis of the cleavage of oligopeptides representing the corresponding nucleocapsid-cleavage sites revealed that all mutations improved cleavability, in good agreement with the previously proposed role of nucleocapsid cleavage in HIV-1 replication.

In vitro processing of HIV-1 nucleocapsid protein by the viral proteinase: effects of amino acid substitutions at the scissile bond in the proximal zinc finger sequence

The human immunodeficiency virus type 1 (HIV-1) nucleocapsid protein flanked by Gag sequences (r-preNC) was expressed in Escherichia coli and purified. HIV-1 proteinase cleaved r-preNC to the "mature" NCp7 form, which is comprised of 55 residues. Further incubation resulted in cleavages of NCp7 itself between Phe16 and Asn17 of the proximal zinc finger domain and between Cys49 and Thr50 in the C-terminal part. Kinetic parameters determined for the cleavage of oligopeptides corresponding to the cleavage sites in r-preNC correlated well with the sequential processing of r-preNC. Mutations of Asn17 were introduced to alter the susceptibility of NC protein to HIV-1 proteinase. While mutating Asn17 to Ala resulted in a protein which was processed in a manner similar to that of the wild type, mutating it to Phe or Leu resulted in proteins which were processed at a substantially higher rate at this site than the wild type. Mutation of Asn17 to Lys or Gly resulted in proteins which were very poorly cleaved at this site. Oligopeptides containing the same amino acid substitutions at the cleavage site of the proximal zinc finger domain were also tested as substrates of the proteinase, and the kinetic parameters agreed well with the semiquantitative results obtained with the protein substrates.

Human immunodeficiency virus type 1 capsid protein is a substrate of the retroviral proteinase while integrase is resistant toward proteolysis

The capsid protein of human immunodeficiency virus type 1 was observed to undergo proteolytic cleavage in vitro when viral lysate was incubated in the presence of dithiothreitol at acidic pH. Purified HIV-1 capsid protein was also found to be a substrate of the viral proteinase in a pH-dependent manner; acidic pH (<7) was necessary for cleavage, and decreasing the pH toward 4 increased the degree of processing. Based on N-terminal sequencing of the cleavage products, the capsid protein was found to be cleaved at two sites, between residues 77 and 78 as well as between residues 189 and 190. Oligopeptides representing these cleavage sites were also cleaved at the expected peptide bonds. The presence of cyclophilin A decreased the degree of capsid protein processing. Unlike the capsid protein, integrase was found to be resistant toward proteolysis in good agreement with its presence in the preintegration complex.