Structural requirements for and consequences of an antiviral porphyrin binding to the V3 loop of the human immunodeficiency virus (HIV‐1) envelope glycoprotein gp120

Abstract

Several porphyrin derivatives were reported to have anti-HIV-1 activity. Among them, meso-teta(4-carboxyphenyl)porphine (MTCPP) and other carboxyphenyl derivatives were the most potent inhibitors (EC50 <0.7 mu M). MTCPP bound to the HIV-1 envelope glycoprotein gp120 and to full-length V3 loop peptides corresponding to several HIV-1 isolates but not to other peptides from gp120 + gp41. However, it remained possible that MTCPP bound to regions on gp120 which cannot be mimicked by peptides. Further characterization of the binding domain for MTCPP is important for understanding the antiviral activity of porphyrins and for the design of anti-HIV-1 drugs interfering with functions of the virus envelope. Results presented here show that: (i) deletion of the V3 loop from the gp120 sequence resulted in drastically diminished MTCPP binding, suggesting that the V3 loop is the dominant if not the only target site on gp120; (ii) this site was only partially mimicked by full-length V3 loop peptides; (iii) MTCPP binding to the gp120 V3 loop elicited allosteric effects resulting in decreased accessibility of the CD4 receptor binding site; (iv) the binding site for MTCPP lies within the central portion of the V3 loop (KSIHIGPGRAFY for the HIV-1 subtype B consensus sequence) and does not involve directly the GPG apex of the loop. These results may help in designing antiviral compounds with improved activity.

Inactivation of Human Immunodeficiency Virus Type 1 by Porphyrins

“…These results showed that an important target of these compounds is the viral Env protein. Neurath et al (26,27) have correlated the anti-HIV activity by using an assay for cytotoxicity on a T-cell line that measures the inhibition of the interaction between gp120 and antibodies specific for the V3 hypervariable loop of this protein. In this series of approximately 20 porphyrins from both the natural and synthetic classes, there was no clear correlation overall between inhibition of antibody binding to gp120 and overall activity in an antiviral assay.…”

“…Protoporphyrin (3), hemin (22,25), and other related natural porphyrins and metalloporphyrins (11-13, 16, 25-29) have been shown to have activity against HIV in the micromolar range in such antiviral assays. Sulfonated derivatives of tetraphenylporphyrin have also been shown to be active (16,28,38) as have other selected tetra-arylporphyrins (11,15,16,(26)(27)(28). The mechanisms of action and the stage in the viral life cycle at which the porphyrins exert their inhibitory effects on HIV-1 are not well understood.…”

“…A third mechanism by which porphyrins may inhibit HIV is via interaction with the envelope (Env) protein. Binding to a sequence in the V3 loop of the HIV-1 Env protein has been reported as a possible mechanism by which such compounds could inactivate viral infectivity (12,(25)(26)(27)38). The V3 loop is a principal antigenic determinant of the external domain of the viral Env protein and is thought to play an important role in viral attachment and penetration (6,36,44,47,50).…”

3-Hydroxyphthaloyl-β-Lactoglobulin. I. Optimization of Production and Comparison with other Compounds Considered for Chemoprophylaxis of Mucosally Transmitted Human Immunodeficiency Virus Type 1

“…For experiments described in Fig. 6, a full length V3loop peptide (1 mg in 0.5 mL PBS) from HIV-1 rrm gp120 (Neurath et al, 1995b) was reduced with 10 mM 2-mercaptoethanol (2-ME) for 1 h at 25°C. The reduced peptide was separated from excess 2-ME by molecular exclusion chromatography on Sephadex G-10 (Pharmacia).…”

A ′Fragment Fitting Approach′ to Model Disulfide Loops by Utilizing Homologous Peptide Fragments from Unrelated Proteins of Known Structures: Application to the V3 Loop of the HIV-1 Envelope Glycoprotein gp120

“…Attempts to gain better understanding of the structure of the third variable domain, designated as V3 loop, of the human immunodeficiency virus (HIV-1) gp120 envelope glycoprotein, a target for anti-HIV drug discovery [12][13][14], was the principal reason for us to model disulfide bonded loops in proteins. This loop, bonded by a pair of invariant cysteines, has been shown to play an important role in virus entry into CD4+ cells and in the tropism and infectivity of HIV-1 [15].…”