Interaction between a membrane‐associated serine proteinase of U‐937 monocytes and peptides from the V3 loop of the human immunodeficiency virus type 1 (HIV‐1) gp120 envelope glycoprotein

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Abstract
A trypsin-like proteinase which is inhibited by recombinant gp120 and by synthetic peptides of various lengths spanning the conserved sequence of the V3 loop has been purified and partially characterized from a U-937 cell membrane extract. V3 loop peptides behave as competitive inhibitors of the enzyme, while gp 120 exerts a tight-binding inhibition, reacting in stoichiometric amounts with the proteinase to provide significant inhibition. Though the properties of the U-937 membrane proteinase towards gp 120 and synthetic peptides of the V3 loop resemble those of the Molt-4 T-cell tryptase TL2, these two proteinases differ by their physicochemical properties and their susceptibility to other inhibitors of serine proteinases. These results give support to the concept of a membrane-associated proteinase as a complementary or alternative receptor to the CD4, for allowing virus to enter host cells and thus spreading HIV infection.