FIG 4.

Comparison of monomer and dimer forms of double-mimetic peptides. (A to C) Monomeric and dimeric Fc fusions of the indicated double-mimetic peptides were assayed by cell-surface binding to 293T cells expressing the envelope glycoprotein of the ADA isolate, as measured by flow cytometry (A); neutralization studies, as described for Fig. 2 (B); and precipitation of [³⁵S]cysteine-labeled gp120 by Fc fusions bound to protein A-Sepharose beads (C). Results shown in panel C are represented as the percentage of maximal binding. (D) A model explaining the precipitation results corresponding to panel C. Monomeric and dimeric 16-Fc and dimeric 1-Fc can engage both receptor sites on free gp120, whereas monomeric 1-Fc can engage only one site. The experiments represented in panels A to C were performed in triplicate, with errors bars indicating standard errors, and are representative of at least two experiments with similar results.