Probing Structural Variation and Dynamics in the HIV-1 Env Fusion Glycoprotein

Background: Recent advances in structural characterization of the HIV envelope glycoprotein (Env) have provided a high-resolution glimpse of the architecture of this target for neutralizing antibodies and the machinery responsible for mediating receptor binding and membrane fusion. These structures primarily capture the detailed organization of the receptor-naive, prefusion conformation of Env, but under native solution conditions Env is highly dynamic, sampling multiple conformational states as well as exhibiting local protein flexibility. Methods: Special emphasis is placed on the use of biophysical methods, including single-molecule fluorescence microscopy and hydrogen/deuterium-exchange mass spectrometry. Results: Using novel biophysical approaches, striking isolate-specific differences in Env's dynamic profile have been revealed that appear to underlie phenotypic differences of the viral isolates such as neutralization sensitivity and CD4 receptor reactivity. Conclusion: Structural studies are complemented by novel biophysical investigations that enable visualization of the dynamics of HIV-1 Env under native conditions. These approaches will also enable us to gain new insights into the mechanisms of action of antibodies and drugs.