HIV Fusion Protein Reduces Membrane Energy Barrier

Researchers studying the interaction between HIV and human T-cells have found that an HIV fusion peptide lowers the energy required for the cell membrane to bend, making it easier for the virus to enter the cell.

The HIV gp120 protein initiates binding of the virus onto the host T-cell. Another protein --gp41--then enables HIV to penetrate the T-cell membrane. Fusion takes place specifically through a short stretch of gp41 called fusion peptide 23 (FP-23). To better understand how FP-23 functions investigators at Carnegie Mellon University (Pittsburgh, PA, USA) used an X-ray diffusion technique to study how this HIV fusion peptide affected the energy of synthetic lipid bilayers that had been designed to mimic normal cell membranes.

Results published in the May 25, 2007, online edition of the Biophysical Journal revealed that the bending modulus of the membrane was greatly reduced upon addition of the HIV fusion peptide FP-23 to lipid bilayers. A smaller bending modulus reduced the free energy barriers required to achieve and pass through the highly curved intermediate states and thereby facilitated fusion and HIV infection. Overall, FP-23 reduced the energy required to penetrate an artificial cell membrane by up to 13-fold, depending on the thickness of that membrane.

"We found that HIV fusion peptide dramatically decreases the amount of energy needed to bend a cell-like membrane,” said first author Dr. Stephanie Tristram-Nagle, associate research professor of biological physics at Carnegie Mellon University. "This helps membranes to curve, a necessary step for HIV to fuse with an immune cell as it infects it. Reducing this energy should help explain in part how HIV infection occurs so readily. Our findings definitely will change how theoreticians think about virus-cell interactions. This same phenomenon could provide a general way that viruses use to infect cells, so it will be exciting to look at other viral systems with our experimental method.”


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