Budding is the final step of HIV infection. Viral particles will have to modify the topology of the plasma membrane in order to achieve their correct release from the infected cell, by recruiting ESCRT proteins at the budding point, and among them CHMP4 and CHMP2 isoforms. So far, the molecular details of this recruitment are not precisely known.. Lethal Giant Discs (LgD) has been descibed in the litterature as a regulator of endosomal trafficking, and an interaction with CHMP4B has been proposed. A major point of this research is to propose a structural basis for this interaction, as well as a better understanding of the role and general organization of LgD/CC2D1A. The crystal structure of a LgD fragment (comprising a predicted coiled-coil motif and a c-terminal C2 domain) was solved in our lab at 2.4 A. Moreover, we show that CC2D1A impairs in vitro the ability of CHMP4B to polymerize. Based on a crystallographic structure of CHMP4B and biochemical data, we also show that the binding site of CC2D1A on CHMP4B is itself involved in polymerization, in the context of HIV budding. As a side project, I've also set up a protocole to obtain pure monomeric CHMP2B, which has been shown to polymerize at the plasma membrane, and I've characterized the protein in the presence of liposomes, along with new partners.
Structure and function of a ESCRT-III ligand, LgD/CC2D1A, involved in HIV virus budding