Structural and Functional Analysis of Negatively Charged Milk Proteins with Anti-HIV Activity

Several polyanionic reagents such as dextran sulfates, heparin sulfates, and negatively charged proteins have been reported to exhibit anti-HIV activity in vitro. Particularly potent inhibition has been reported for the milk protein β-lactoglobulin (βLG) on modification by 3-hydroxyphthalic anhydride (3HP). The introduction of multiple negatively charged carboxyl groups along the polypeptide backbone obviously leads to repulsion within the protein molecule and this is likely to affect the specific tertiary, and perhaps also secondary, structure of the protein. We used several biophysical techniques to probe the structural changes that occur on 3HP modification of βLG. The results suggest that the protein becomes largely unstructured on chemical modification. Although a profound anti-HIV activity was measured for 3HP-βLG, similar antiviral effects were observed with two other 3HP-modified milk proteins, α-lactalbumin and αS2-casein, but not with the unmodified proteins. Most potent inhibition of HIV-1 repl...