Chemical Synthesis of the Aspartic Proteinase from Human Immunodeficiency Virus (HIV)

Abstract

An aspartic proteinase encoded by the human immunodeficiency virus (HIV) is expressed during the course of infection leading to acquired immunodeficiency syndrome (AIDS). This enzyme is essential for viral infectivity and proliferation; it selectively cleaves all viral protein components from a “polyprotein” precursor molecule (1). It is essential for the production of fully competent virus and is unique to a class of retrovirally encoded aspartic proteinases with no apparent counterpart in the mammalian realm. As such, it is an ideal target for design of specific inhibitors as antiviral therapeutic agents for the treatment and perhaps cure of AIDS. Critical to this effort has been availability of the enzyme for structure-function analysis. The three-dimensional structure of the enzyme, derived from X-ray crystallographic efforts, was determined in 1989 by Wlodawer et al. (2). Diffraction-quality crystals of the HIV-l proteinase were obtained from chemically synthesized protein corresponding to the sequence of the SF-2 isolate from an AIDS-associated retrovirus (ARV-2) as reported by Sanchez-Pescador et al. (3). This particular protein was synthesized using t-Boc/benzyl strategy starting with Phe-PAM resin following a highly optimized synthetic regimen described previously by Schneider and Kent. In their synthesis, cysteine occurring at positions 67 and 95 in the native sequence was replaced with α-aminobutyric acid (Abu), an isosteric analog of cysteine, i.e., a methyl group replaces the thiol moiety (4).