FIG 2.

Sensitivity to cold inactivation is determined by the propensity of Envs to undergo structural changes at 0°C and by the stability of the induced state. (A) Restructuring of Env precedes changes in function. The effects of incubation at 0°C on binding of MAb 17b (bottom) and virus infectivity (top) were compared for the indicated Envs. Binding and infectivity are expressed as the fold change in values relative to samples incubated at 37°C. (B) Effect of cold on MAb 17b binding to Envs. The sensitivity of each Env to inactivation at 0°C is represented by the color of the line (red, resistant; yellow, intermediate; green, sensitive). The data describe the absolute binding efficiency of MAb 17b (in relative light units [RLU]). (C) Variants of 89.6 Env tested in this study. Differences in sequence between 89.6 and KB9 Envs are shown. Vertical bars represent mutations introduced to revert sequence to the amino acid found in the similarly colored Env (89.6, blue; KB9, pink). (D) Cold-induced inactivation of virus containing variants of the 89.6 Env. (E) Relationship between binding of MAb 17b to Envs at 37°C and 0°C. To correct for differences in Env expression between variants, binding of MAb 17b was normalized to binding of MAb 2G12. The sensitivity of Envs to inactivation at 0°C is represented by the color of the lines (red, resistant; green, sensitive). (F) Rates of cold-induced exposure of CoR-BS. Probe binding to Env-expressing HOS cells incubated at 0°C for the indicated times is shown. Binding is expressed relative to that of samples incubated at 37°C.