A novel soluble analog of the HIV-1 fusion cofactor, globotriaosylceramide (Gb3), eliminates the cholesterol requirement for high affinity gp120/Gb3 interaction

Abstract

We have analyzed the interaction of adamantyl Gb 3 (adaGb 3 ), a semi-synthetic soluble analog of Gb 3 , with HIV-1 surface envelope glycoprotein gp120. In this analog, which was orginally designed to inhibit verotoxin binding to its glycolipid receptor, Gb 3 , the fatty acid chain is replaced with a rigid globular hydrocarbon frame (adamantane). Despite its solubility, adaGb 3 forms monolayers at an air-water interface. Compression isotherms of such monolayers demonstrated that the adamantane substitution resulted in a larger minimum molecular area and a more rigid, less compressible film than Gb 3 . Insertion of gp120 into adaGb 3 monolayers was exponential whereas the gp120/Gb 3 interaction curve was sigmoidal with a lag phase of 40 min. Adding cholesterol into authentic Gb 3 monolayers abrogated the lag phase and increased the initial rate of interaction with gp120. This effect of cholesterol was not observed with phosphatidylcholine or sphingomyelin. In addition, verotoxin-bound adaGb 3 or Gb 3 plus cholesterol was recovered in fractions of comparable low density after ultracentrifugation through sucrose-density gradients in the presence of Triton X-100. The unique biological and physico-chemical properties of adaGb 3 suggest that this analog may be a potent soluble mimic of Gb 3 , providing a novel concept for developing GSL-derived viral fusion inhibitors. -Mahfoud, R., M. Mylvaganam, C.A. Lingwood, and J. Fantini. A novel soluble analog of the HIV-1 fusion cofactor, globotriaosylceramide (Gb 3 ), eliminates the cholesterol requirement for high affinity gp120/Gb 3 interaction.

Glycosphingolipids in HIV/AIDS: The Potential Therapeutic Application

“…In contrast, a distinct fluorescent band was formed for Gb 3 +cholesterol. However adaGb 3 formed the strongest labeled 'raft' band (Mahfoud et al, 2002b). While the characteristics of the structures formed by adaGb 3 in this band remain to be fully characterized, this supports the "raft-like" character of adaGb 3 .…”

“…In collaboration with Fantini's group , we showed that gp120 can insert into a Gb 3 monolayer at the water/air interphase in a Langmuir trough (Mahfoud et al, 2002b). However, there was a 2 hour lag-phase prior to binding/insertion which then proceeded at a sigmoidal rate.…”

“…We have shown that cholesterol is one requirement. A fifty fold molar excess of the SPC3 peptide from the glycolipid binding V3 loop of gp120 of HIV, which strongly binds adaGb 3 (Mahfoud et al, 2002b) is able to eliminate FITC-VT1 B falciparum, which causes malaria. Following attachment of the P. falciparum merozoite to erythrocytes, the membrane invaginates taking up the parasite within a parasitophorous vacuolar membrane (PVM) (Haldar et al, 2002).…”

“…Several studies have shown that the binding of the gp120 HIV adhesin to GSL is dependent not only on the carbohydrate, but also the lipid moiety of the GSL , Mahfoud et al, 2002b, Villard et al, 2002. The interaction of GSLs with cholesterol is modulated by the fatty acid chain length and the binding of HIV gp120 to Gb 3 /cholesterol vesicles has been shown to be a function of the fatty acid composition in that C16 fatty acid Gb 3 was bound but C17, C18 and C20 Gb 3 were not.…”

Synthesis of Highly Water-Soluble Adamantyl Phosphoinositide Derivatives

“…[16] The aqueous solubility of the resulting compounds has been reported to be significantly increased, which could be attributed to the formation of low-order aggregates. [16,17] In addition, the rigid globular hydrocarbon framework of adamantane groups may facilitate the crystallisation processes. Furthermore, they may also mimic the actual behaviour and conformation of the long acyl chains of naturally occurring phosphoinositides in vivo when exposed to the buffer-like cytosolic environments.…”