The discovery, presented at the 12th annual Conference on Retrovirus and Opportunistic Infections in Boston, and simultaneously published in newest issue of the British journal Nature, shows how HIV mutates its form, in turn provoking changes which permit it to enter cells.

The study was done at the Boston Children's Hospital and Harvard Medical School by Stephen Harrison, head of a research team at the Howard Hughes Medical Institute.

The scientists were able to obtain a three-dimensional image of the protein gp120, an element of the HIV membrane, before it metamorphoses itself and attaches to a cell's so-called CD4 receptors.

Once the protein attaches to the receptors, HIV is able to penetrate the cell's interior and reproduce, explained one of the scientists.

The scientists said that understanding gp120's shape changes before the attack on cells could lead to the creation of new vaccines to inhibit HIV infections.

"Knowing how gp120 changes shape is a new route to inhibiting HIV by using compounds that inhibit the shape change," said Harrison.

"The findings also will help us understand why it's so hard to make an HIV vaccine, and will help us start strategizing about new approaches to vaccine development," he said.

Harrison revealed that there are already some inhibitors in development which apprently restrict the shape change of the protein.

The work "might provide a route to new vaccine or drug strategies," Harrison said.

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