FIG. 4.

Energy barriers, lifetimes, and molecular elastic constant of bonds between Env glycoprotein and cellular receptors. (A and B) Time-dependent minimum value of the free energy (ΔG^‡) describing the binding adhesion interactions between Env glycoproteins and receptors on CD4⁺ CCR5⁻, CD4⁺ CCR5⁺, CD4⁻ CCR5⁺, and CD4⁺ CXCR4⁺ cells in the absence (A) and the presence (B) of small-molecule inhibitors. (C and D) Time-dependent molecular spring constants, κ_m, of gp120-CD4 and gp120(sCD4)-CCR5 bonds in the absence (C) and the presence (D) of small-molecule inhibitors. (E and F) Time-dependent distance from the free energy minimum to the point of bond rupture, x^‡, of gp120-CD4 and gp120(sCD4)-CCR5 bonds in the absence (E) and presence (F) of small-molecule inhibitors. Data were collected with a retraction velocity of 10 μm/s.