Briggs and researchers at the Max Planck Institute for Biochemistry have discovered the mechanism behind a crucial step in the HIV life cycle. In collaboration with teams from Heidelberg University and Yale University, they revealed that the mysterious "spacer peptide 2" (one of the HIV viral components) plays a key role in transforming immature HIV-1 particles into infectious particles. The research results have been published in the journal Nature. Key processes in HIV maturation HIV needs to undergo a maturation process to become infectious, which involves rearrangements in the structure of the matrix protein (red). In immature virus particles, the matrix protein forms a loose lattice structure (top right), while in mature HIV, the binding of spacer peptide 2 triggers the formation of a new, more stable lattice structure (blue, bottom right). © Illustration: Margot Riggi, MPI of Biochemistry. HIV-1 particle maturation HIV-1 particles are initially released from infected cells in an immature, non-infectious form. The main building block of the virus particle is about 2,000 copies of a long rod-shaped protein called Gag. To be able to infect host cells, HIV must go through a maturation process that involves the cleavage of Gag by HIV-1 protease (a viral enzyme), breaking it down into six smaller proteins, including the capsid protein and the matrix protein. This cleavage process results in a huge rearrangement of the virus's internal structure. Although scientists have been exploring structural changes in the viral capsid that envelops the genome for many years, comparatively little is known about the virosome, the protein shell beneath the lipid membrane…