The connection domain is implicated in metalloporphyrin binding and inhibition of HIV reverse transcriptase.

We have shown that heme and zinc protoporphyrin inhibit both human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2) reverse transcriptases (RTs) and, in combination with other nucleoside and non-nucleoside inhibitors, exert an additive effect on HIV-1 RT inhibition. Screening of a phage peptide library against heme resulted in the isolation of a peptide with sequence similarity to sequence 398-407 from the connection subdomain of both HIV-1 and HIV-2 RTs, suggesting that this highly conserved region of HIV RTs corresponds to the binding site for metalloporphyrins and a new site for inhibition of enzyme activity. Inclusion of a synthetic peptide corresponding to the exact sequence 398-407 of HIV-1 RT in RT inhibition assays had a protective effect on metalloporphyrin inhibition, as it was able to reverse the inhibitory effect of both metalloporphyrins on HIV-1 RT activity. Furthermore, intrinsic fluorescence assays indicated that these metalloporphyrins bind to synthetic peptide 398-407 as well as to intact dimeric HIV-1 RT. The identification of this novel inhibition site will help to expand our understanding of the mode of action of metalloporphyrins in RT inhibition and will assist in the design and development of more potent metalloporphyrin RT inhibitors for the management of HIV infection.