(A) Transmission electron microscopy image of an authentic negative stained HIV-1 capsid. The capsid is formed of hundreds of CA proteins organized in hexamers and pentamers. (B). The structure of a CA hexamer, revealed by X-ray crystallography (PDB ID: 3H47). (C). Detail of the small molecule IP6 (IP6; in the center) binding to a ring of six arginines (R18; on the outside) within the R18 pore at the center of a CA hexamer. IP6 contains six negatively charged phosphate groups , which are coordinated by the positively charged guanidino groups of the R18 side chains. Dashed lines indicate interactions between the guanidino and phosphate groups (Panel C is adapted from Mallery et al., 2018).