Comparative purification of recombinant HIV-1 and HIV-2 reverse transcriptase: preparation of heterodimeric enzyme devoid of unprocessed gene product

Cloning, expression, purification, and crystallisation of HIV-2 reverse transcriptase

A purification procedure is described for the isolation of recombinant HIV-2 reverse transcriptase expressed in Escherichia coli. The p68 subunit is expressed, in the absence of induction, and use of a heparin-Sepharose column produces substantially pure protein. Concentration of the homodimeric p68 reverse transcriptase pool, followed by incubation at room temperature for several days, results in full conversion by E. coli proteases to the heterodimer (p68/p55). This extended incubation simplifies the purification process and improves the yield of heterodimeric reverse transcriptase, which shows a truncation of the smaller subunit to 427 residues. The protein is then purified further by hydroxyapatite and gel-filtration chromatography to homogeneity. The HIV-2 RT is active and has been used to produce crystals that diffract to beyond 3.0 A.

High-performance liquid chromatography and photoaffinity crosslinking to explore the binding environment of nevirapine to reverse transcriptase of human immunodeficiency virus

Nevirapine (BI-RG-587) is a potent inhibitor of the polymerase activity of reverse transcriptase of human immunodeficiency virus type-1. Nevirapine, as well as several other non-nucleoside compounds of various structural classes, bind strongly at a site which includes tyrosines 181 and 188 of the p66 subunit of reverse transcriptase. The chromatography which was utilized to explore this binding site is described. BI-RH-448 and BI-RJ-70, two tritiated photoaffinity azido analogues of nevirapine, are each crosslinked to reverse transcriptase. The use of several HPLC-based techniques employing different modes of detection makes it possible to demonstrate a dramatic difference between the two azido analogues in crosslinking behavior. In particular, by comparing HPLC tryptic peptide maps of the photoadducts formed between reverse transcriptase and each azido analogue, it can be shown that crosslinking with BI-RJ-70 but not with BI-RH-448 is more localized, stable, and hence exploitable for the identification of the specifically bonded amino acid residue(s). In addition, comparison of the tryptic maps also makes it feasible to assess which rings of the nevirapine structure are proximal or distal to amino acid side chains of reverse transcriptase. Finally, another feature of the HPLC peptide maps is the application of on-line detection by second order derivative UV absorbance spectroscopy to identify the crosslinked amino acid residue.