Discovery of the function of a HIV building block 

HIV (Human Immunodeficiency Virus) is the pathogen that causes acquired immunodeficiency syndrome, AIDS. Infected cells release immature HIV particles. These virus particles undergo a maturation process in order to become infectious. The cleavage of the Gag polyprotein releases the so-called spacer peptide 2 (SP2). Using cryo-electron microscopy, we have shown for the first time how the outermost protein shell rearranges from a loose to a stable lattice and how this is stabilized by SP2 – an important discovery in understanding the formation of mature HIV particles.