A neutralizing epitope of human immunodeficiency virus type 1 has homologous amino acid sequences with the active site of inter-α-trypsin inhibitor

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Abstract
A neutralizing epitope (epitope β) of the HTLV-1118 strain of HIV-1 was mapped to 24 amino acids of an external envelope glycoprotein (gp120) using a neutralizing monoclonal antibody (0.5β) and hetero-antisera against synthetic peptides encoding gp120. Proteins that have homologous sequences with epitope β were sought from a databank of protein sequences to assess biological features of epitope β. The resutts showed that epitope β was found to have homologous sequences to inter-α-trypsin inhibitor (ITI). The homologous region of ITI included the active site of the protein. Synthesized peptides including epitope β were good substrates for trypsin, because these peptides inhibited trypsin activities in a competitive manner (K1 = 24.5 μM). Human urlnary trypsin inhibitor (UTI), a protein indistinguishabie from ITI, as well as synthetic peptides including epitope β inhibited syncytlum formation caused by the LAV-1-infected CCRFCEM and uninfected Molt-4 cells in a dose-dependent manner (0.1-1 mM). These findings suggest that epitope β of HIV-1 could be substrate of protease upon HIV-1 infection and also suggest that protease inhibitory activity of epitope β may play a role in the pathophyslology of HIV-1-infected individuals.

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